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University of Groningen The Kenyan hippo Kanga, Erustus Mutembei IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite from it. Please check the document version below. Document Version Publisher's PDF, also known as Version of record Publication date: 2011 Link to publication in University of Groningen/UMCG research database Citation for published version (APA): Kanga, E. M. (2011). The Kenyan hippo: Population dynamics, impact on riparian vegetation and conflicts with humans Groningen: s.n. Copyright Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons). 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Download date: 14-06-2017 The Kenyan Hippo Population dynamics, impacts on riparian vegetation and conflicts with humans The research for this thesis was carried out in the Community and Conservation Ecology Group at the Center for Ecological and Evolutionary Studies (CEES) of the University of Groningen, The Netherlands Lay-out and figures: Cover: Photos: Printed by: Dick Visser Erustus Kanga Erustus Kanga, Felix Micheni (p. 18) Van Denderen BV, Groningen ISBN: 978-90-367-5132-2 ISBN: 978-90-367-5133-9 (digital version) RIJKSUNIVERSITEIT GRONINGEN The Kenyan Hippo Population dynamics, impacts on riparian vegetation and conflicts with humans Proefschrift ter verkrijging van het doctoraat in de Wiskunde en Natuurwetenschappen aan de Rijksuniversiteit Groningen op gezag van de Rector Magnificus, dr. E. Sterken, in het openbaar te verdedigen op vrijdag 14 oktober 2011 om 14.30 uur door Erustus Mutembei Kanga geboren op 23 december, 1969 te Meru, Kenia Promotor: Prof. dr. H. Olff Co-promotor: Dr. J.O. Ogutu Beoordelingscommissie: Prof. dr. A.J. Hester Prof. dr. H. de Kroon Prof. dr. J.P. Bakker Contents Chapter 1 General Introduction and Study Rationale 7 Chapter 2 Human-hippo conflicts in Kenya during 1997-2008: Vulnerability of a megaherbivore to anthropogenic land use changes 19 Chapter 3 Population trend and distribution of the Vulnerable common hippopotamus Hippopotamus amphibius in the Mara Region of Kenya 33 Chapter 4 Hippopotamus and livestock grazing near water points: consequences for vegetation cover, plant species richness and composition in an East African Savannah 47 Chapter 5 Hippopotamus and livestock grazing: influences on riparian vegetation and facilitation of other herbivores in the Mara Region of Kenya 67 Chapter 6 Hippopotamus as agents of change on riparian-edge communities: A synthesis 87 References 97 Summary / Samenvatting 111 Acknowledgements 121 List of publications 125 Affiliation of co-authors 126 Curriculum Vitae 127 Chapter one 1 General Introduction and Study Rationale Introduction Many countries in sub-Saharan Africa host large and world-famous conservation estates some of which are hotspots of unique biodiversity and ecosystem processes and offer excellent opportunities for ecotourism. Nonetheless, numerous changes have markedly modified both protected and non-protected areas in many of these countries in recent decades with significant consequences for biodiversity conservation and human well-being. Marked increases in human populations, shifts in cultural traditions and land tenure arrangements and rising demand for land for human settlements, crop and livestock production and other uses have fundamentally altered land use patterns (Meyer and Turner 1994; Foley et al. 2005). The impacts of these land use changes are further compounded by climatic changes due to global warming, thereby posing major challenges to efforts to conserve and sustain biodiversity, key ecosystem processes and services in protected and nonprotected areas, especially in dryland savannas (Ogutu and Owen-Smith 2003, Holmgren et al. 2006; Li et al. 2006). These changes often have asymmetrical effects on neighboring protected and non-protected ecosystems and thus alter the nature and strength of critical ecosystem connectors and flows. Marked impacts of land use changes are evident in Kenyan ecosystems regardless of their conservation status and include loss of wildlife habitats in savanna rangelands, degradation, fragmentation and loss of wildlife migratory corridors, restricted access to water, spiraling human-wildlife conflicts, loss of biodiversity and declining wildlife abundance (Prins 1992; Verlinden 1997; Homewood et al. 2001; Serneels and Lambin 2001). The Masai Mara Region of Kenya (Mara), which forms the northernmost part of the Serengeti-Mara Ecosystem, exemplifies savanna rangelands experiencing major perturbations in recent decades. Although the Maasai and their livestock have long coexisted harmoniously with wildlife in the Mara; that harmony is now being increasingly threatened by human population growth and expansion of settlements, diversification of livelihood options, privatization of formerly communally owned lands, among other changes (Lamprey and Reid 2004; Ogutu et al. 2009). The changing land tenure has encouraged cultivation, permanent settlements, including development of urban centers, and intensification of land use with the result that traditional wildlife habitats have contracted and wildlife numbers and diversity declined (Thompson and Homewood 2002; Ottichilo et al. 2001; Serneels and Lambin 2001). African savannas support diverse assemblages of indigenous large herbivores supplemented by livestock (Skarpe 1991) whose grazing and browsing activities shape many ecosystem processes, including creating and maintaining spatial heterogeneity in landscapes (McNaughton 1984, 1985; Illius and O’Connor 2000; Ogutu et al. 2010). Human activities and location of water sources additionally influence ecosystem structure and function, in particular the spatial and temporal 8 Chapter 1 distribution of wild herbivores and livestock (Western 1975; Verlinden 1997, de Leeuw et al. 2001; Redfern et al. 2003; Ogutu et al. 2010). This is especially true for the Mara, in which water availability becomes progressively limited and water sources become points of contacts and conflicts between wild herbivores, the pastoral Maasai and their livestock during the dry season. However, although the Serengeti-Mara is the most well studied savanna ecosystem in Africa in both its ecological and human dimensions, with detailed background knowledge available on community and ecosystem processes, the ongoing sendentalization of the pastoral Maasai and increased livestock concentrations, especially around water sources, have exposed glaring gaps in our knowledge and understanding of how these processes alter biodiversity, particularly in riparian-edge habitats, that are key resources zones during dry seasons. Within the riparian habitats of the Mara, the common hippopotamus Hippopotamus amphibious Linnaeus 1758 and livestock are the main resident grazers. Due to their strong water dependence, both hippos and livestock heavily utilize the riparian habitats year-round and so have the potential to compete for grazing resources. Furthermore, because hippo and livestock grazing can differentially modify vegetation structure, they may have contrasting effects on plants and other herbivore species (Lock 1972; Walker et al. 1987; Harrington et al. 1999; Eltringham 1999; Fleischner 1994; Thrash 2000). I thus undertook this study to analyze (1) human-hippo conflicts in Kenya over the 12-year period covering 1997-2008, (2) hippo population dynamics in the Mara during 1958-2006 and (3) the pattern and consequences of hippo and livestock grazing in the riparian habitats of the Mara on vegetation structure, species richness and composition and herbivore abundance and diversity under protection in the Masai Mara National Reserve and traditional pastoralism in the adjoining pastoral ranches. Mara Region The riparian habitats that formed the main focus of this study are part of the Mara River Basin that covers some 13,750 km2, and is located between 37.78°E and 0.43°S in southwestern Kenya and 33.78°E and 1.48°S in northern Tanzania. The basin is shared between Kenya and Tanzania, with an upper basin area of about 8,941 km2 (65%) in Kenya and a lower basin area of about 4,809 km2 (35%) in Tanzania (WREM 2008). The basin is the catchment area for the Mara River and is also an important habitat for people and wildlife (Fig. 1.1). The basin is characterized by a diversity of land use patterns ranging from natural forests in the upper reaches to large-scale mechanized farms, smallholder subsistence farms, communal pastoral grazing lands, protected open savanna grasslands and wetlands. The upper Introduction 9 AFRICA N 50 km Figure 1.1 Site map of the trans-boundary Mara River Basin, showing the Mara River with its tributaries. reaches of the basin is at about 2,915 m asl, and comprises escarpments that constitute the Mau Forests in Kenya, receiving an average of 1,400 mm of rainwater annually. This rainwater infiltrate through the soil into Enapuyapui swamp to form the Nyangores and Amala rivers, that are the source and only perennial tributaries of the Mara River (WREM 2008; Fig. 1.1). The Mara River meanders through Maasai pastoral ranches and the Masai Mara National Reserve (MMNR). In the MMNR, two other main but seasonal tributaries, the Talek and the Sand Rivers, join the Mara River. The mainstream Mara River continues flowing through the savannah grasslands of the northern Serengeti National Park (SNP) before entering the Mara Swamp and discharging into Lake Victoria (Fig. 1.1). Thus, the Mara River is part of the Lake Victoria drainage system and the greater Nile River Basin. The lowlands and wooded savannah grasslands that form the Maasai pastoral ranches, MMNR and northern SNP receive an average annual rainfall ranging from about 500 mm in the southeast to 1200 mm in the northwest (Norton-Griffith et al. 1975), hence the flow of Mara River provides the only permanent source of surface water for the Maasai pastoralists, their livestock and wildlife. In addition, the Mara River sustains one of the greatest spectacles of the natural world; the annual 10 Chapter 1 migration of wildebeest Connochaetes taurinus Burchell 1823, Burchell’s zebra Equus burchelli Gray 1824 and Thomson’s gazelle Gazella thomsoni Günther 1884 that arrive in the Mara Basin during the dry season in search of water and forage (Pennycuick 1975; Maddock 1979). Consequently, the Mara River also sustains a thriving tourism industry built around this natural phenomenon. In addition, the Mara River supports livelihoods of the pastoral communities and their livestock, and is an important shelter and day-living habitat for the common hippopotamus resident in the Mara River Basin. However, the basin is facing serious and numerous environmental problems primarily created by wide spread encroachment on protected forests and the savanna rangelands for settlement and cultivation (Mutie et al. 2005; Mati et al. 2008). These specifically include: (i) deforestation resulting from encroachment and human settlement in the Mau forests; (ii) soil erosion and high sediment loads in the Mara River; (iii) human-wildlife conflicts resulting from small and large-scale farming that has extended into wildlife range and corridors; (iv) increased frequency and intensity of floods and droughts due to climate variability and land use change; (v) declining water quality and quantity due to poor agricultural practices and excessive water abstractions. The focal species The common hippopotamus, commonly referred to as hippo, is an unmistakable species, with a barrel-shaped, almost hairless body weighing about 1500 to 3000 kg (Kingdon 1982; Eltringham 1999). It is adapted to semi-aquatic habitats, and therefore it is never found far from water. Hippos have featured in human affairs since at least the time of Pharaohs, where they were venerated as gods and have been portrayed in art down the ages (Eltringham 1999). Therefore, it is surprising that in an intensely studied savanna like the Serengeti-Mara ecosystem, the hippo has largely been overlooked (see Sinclair and Norton-Griffiths 1979; Sinclair and Arcese 1995; Sinclair et al. 2008). Nonetheless, the hippo is an exceptional megaherbivore (Owen-Smith 1988) within the Mara River Basin, and it differs from other megaherbivores in having a dual requirement of a shelter and day-living space in water and an open grazing range often visited at night (Eltringham 1999). In coining the term megaherbivore, Owen-Smith (1988) grouped together all terrestrial large herbivores with an adult body weight greater than 1000 kg. Other megaherbivores within the Mara include the African Elephant Loxodonta africana Blumenbach 1797, Black Rhino Diceros bicornis Drummond 1826 and giraffe Giraffa camelopardalis Linnaeus 1758. Owen-Smith (1988) emphasized that the large body size of megaherbivores renders them largely immune to non-human predation and they can generally tolerate food of a lower quality than that required by other herbivores. Owen-Smith (1988) further suggested that megaherbivores Introduction 11 would therefore be less affected by predation or environmental fluctuations like drought and that their populations would be maintained at high densities causing heavy sustained impacts upon their environments. Nevertheless, hippos maintain short grazing lawns in areas that they graze, suggesting that they also enjoy high quality food. In addition, hippos can be vastly affected by environmental fluctuations especially prolonged droughts and above-average rainfall (Marshall and Sayer 1976; Smuts and Whyte 1981). Historically, hippos were found throughout sub-Saharan Africa, but most populations have greatly declined in size while others have disappeared, with the largest populations remaining in East Africa (Eltringham 1999; Lewison and Oliver 2008). Although not strictly nocturnal, hippos typically forage for food at night, and spend the day digesting their food, sleeping and socializing (Klingel 1991). Hippos have a chambered stomach and are referred to as ‘pseudo-ruminants’, and their digestive system can effectively ferment grasses and other low quality foods (Eltringham 1999). Various studies claim that their diet consists predominantly, or solely, of grasses (Field 1970; Oliver and Laurie 1974; Mackie 1976; Scotcher et al. 1978; Kingdon 1982; Eltringham 1999) but recent studies have challenged this assumption and described their diet as variable (Mugangu and Hunter 1992; Boisserie et al. 2005; Cerling et al. 2008), with a few incidences of scavenging on carcasses reported (Dudley 1996). The primary threats to hippos are loss of essential grazing lands to cultivation and encroaching human settlement, unregulated or illegal hunting (Weiller et al. 1994; Eltringham 1999; Williamson 2004; Conservation 2006; Lewison and Oliver 2008) and the growing pressure on fresh water resources across Africa (WWC 2003) that has often resulted in loss of their habitats. Due to increasing human population and agricultural expansion and development in and around wetlands, hippos often run into frequent conflict with people. In addition, hippos have notorious crop-raiding tendencies and can extensively damage the range through grazing and trampling when they occur at high densities (Lock 1972; Thornton 1971; Mkanda and Kumchedwa 1997; Eltringham 1999). The protection of riparian and wetland habitats is currently therefore a pressing priority for hippopotamus conservation, including measures to prevent the drying-up of water courses and loss of riparian-edge grazing ground. Hippos are important to the ecology of permanent wetlands in Africa and exert significant environmental impacts (Olivier and Laurie 1974). Their regular movements from water pools used during the day to adjacent grazing areas utilized at night create trails, modify river channel geomorphology, and assist in developing micro-topography (Naiman and Rogers 1997; McCarthy et al. 1998; Deocampo 2002), with consequences for other organisms. Their trampling and grazing impacts directly or indirectly control the availability of resources for other organisms along the riparian habitats, through physical modification, maintenance, or creation of micro-habitats. At moderate densities, hippos can be beneficial to the ecology of an 12 Chapter 1 area through their maintenance of habitat mosaics while at high densities they can cause intense grazing, soil erosion and may decrease plant and other wildlife abundance and diversity (Field 1970; Thornton 1971; Lock 1972; Olivier and Laurie 1974; Eltringham 1999; Arsenault and Owen-Smith 2002). In addition, the short, hippo-grazed grasses along the riparian habitats create biological barriers to fire, further influencing biodiversity of riparian communities. Hippos pond and create water pools that are important refugia for aquatic organisms. They stir the water, prevent development of anoxic conditions, while their dung fertilizes water, and alter the dynamics of nutrients and particulate matter, promoting primary production, especially fish life which in turn feed crocodiles and birds and numerous other aquatic organisms (Naiman and Rogers 1997; Gereta and Wolanski 1998; Wolanski and Gereta 1999; Mosepele et al. 2009). Thus even though they are less studied in the Serengeti-Mara ecosystem, hippos may have significant non-trophic impacts on the structure, function and biodiversity of this ecosystem. The creation and modification of riparian habitat structures by hippos is an important mechanism generating landscape-scale heterogeneity and is synonymous with physical ecosystem engineering (Jones et al. 1994, 1997; Write et al. 2002). However, there has been little recognition of the importance of hippos and their influence in shaping the riparian habitat mosaics and environments across Africa (but see Olivier and Laurie 1974). Here I present a study on the grazing and trampling effects of hippos within a savanna riparian community and explore the feedback from the abiotic environment along rivers to hippo grazing, the responses of plants and other herbivore species to the changed abiotic conditions, in the protected reserve and the adjacent pastoral system in the Mara Region of Kenya. I assess differences in patterns of responses of plant and herbivore species abundance and richness to hippo and livestock grazing and how these patterns are modified by protection versus pastoralism. Research Hypotheses H1: Vegetation height and cover will increase with distance from water in response to declining grazing intensities This hypothesis predicts that vegetation height and cover will increase with increasing distance from water sources, due to declining grazing intensities from water (Fig. 1.2). The consequences of this hypothesis are that hippopotamus grazing will further contribute directly to patchiness in grasslands through defoliation and trampling within a restricted strip along the riparian zone, aiding spatial heterogeneity of landscapes at intermediate distances from rivers. Introduction 13 intermediate grazing intensity distance grass >30 cm percentage cover grass <10 cm grass 10–30 cm forbs+shrubs distance from rivers Figure 1.2 Hypothesized response of vegetation cover components, grass <10 cm high, grass 10–30 cm, grass >30cm and forbs and shrubs to distance from rivers as a function of declining grazing intensity. H2: Plant species richness will increase with distance from rivers in response to declining grazing intensities This hypothesis predicts that plant species richness will increase with increasing distance from rivers in response to declining grazing and trampling intensity. The heavily grazed and trampled areas close to river banks will have low plant species richness except for forb species. The distribution and abundance of forbs is expected to respond positively to grazing intensity and the species abundance and richness of forbs to decline with distance from rivers (Fig. 1.3). Grass species will increase with distance from rivers as grazing intensity declines while shrub species will establish in areas of high grazing intensity and decline with distance from rivers as grazing intensity declines. number of species grass forbs shrubs distance from rivers Figure 1.3 Hypothesized response of plant species, forbs, grass and shrubs with distance from rivers as a function of declining grazing intensity. 14 Chapter 1 H3: Herbivore abundance and species richness will increase with increasing distance away from rivers due to a corresponding increase in forage availability This hypothesis predicts spatial variation in herbivore abundance and distribution with distance from rivers and along the distance-to-river gradient. Hippo grazing along riparian areas will facilitate some herbivore species and cause competitions with others. In addition, hippo grazing will influence predation risk for herbivores, as the cover of tall vegetation increases with distance from rivers, with varying effects on different herbivore foraging guilds. The dry seasons will further force herbivores to congregate close to rivers, amplifying habitat stress especially in the pastoral ranches grazed heavily by livestock. Herbivore use of the riparian habitats in the pastoral ranches will be constrained by human presence and livestock herding. Herbivores that are more water dependent and require high food quality will decline with distance from rivers. Herbivores that are bulk feeders will increase with distance from rivers. Herbivores that are less water dependent will be uniformly distributed relative to distance to rivers. In general, a humped distribution will describe the distribution of the abundance of most herbivores along the distance-to-river gradient (Fig. 1.4; Ogutu et al. 2010). bulk feeders food quality quantity/quality water independent response generalized herbivore response distance from rivers Figure 1.4 Hypothesized response of herbivores that are, water dependent and sensitive to food quality, bulk feeders, and water independent and generalized herbivore response along grazing gradients from rivers. Research Questions I attempted to find answers to the following three questions. (1) How does the pattern of human-hippo conflicts throughout Kenya vary over time and what does this variation imply for the future of hippo conservation in Kenya? (2) How do Introduction 15 long-term hippo population dynamics respond to changing land use and climatic variability and compare with the dynamics of other megaherbivores in Kenya? (3) What are the impacts of hippo grazing on vegetation and other herbivores and how are these impacts modified by land use? In particular, how does the impact of hippopotamus grazing and trampling on (1) bare ground cover, (2) vegetation cover and height, (3) plant species richness and composition, (4) herbivore abundance and species richness vary along the distance-to-river gradient and with protection and pastoralism? Thesis outline This thesis is organized in 6 chapters as follows. Chapter 1 serves as an introduction and provides brief background information on anthropogenic effects on the distribution and abundance of herbivores in savannah ecosystems. The chapter also provides background information on the Mara River Basin that is the focus landscape for most of this study. This chapter also highlights the ecological importance of hippos in African wetlands. Finally, the chapter presents the three main hypotheses and research questions explored in greater detail in subsequent chapters of this thesis. Chapters 2 and 3 cover the conservation and management of hippopotamus in Kenya. Chapter 2 presents an analysis of human-hippo conflicts throughout Kenya during 1997 to 2008. Very few studies have directly addressed the problem of human-hippo conflicts in Kenya, thus, there has been major gaps in information on this topic. Given the importance that the Kenya Wildlife Service (KWS) attaches to wetlands and threatened species conservation, analysis of the long term monitoring data that KWS collects on human-hippo conflicts in Kenya is clearly useful. This chapter thus examines key management issues on human-hippo conflicts, identifying the extent, severity and distribution (spatial and temporal) of hippo-related damages to crops and how retaliatory killings of hippos are threatening and undermining hippo conservation efforts in Kenya. This chapter highlights the fact that conflicts between people and hippopotamus in Kenya probably cannot be entirely eliminated but can be mitigated, by discouraging agricultural activities associated with high human density on lands bordering riparian habitats and promoting conservation and sustainable use of wetlands. Chapter 3 explores the population status and conservation of hippopotamus at one of Kenya’s important conservation area, the Masai Mara. Despite its imposing size and formerly large abundance, the common hippopotamus has been much less studied in Kenya compared to other Megaherbivores. Thus, this chapter also fills this important gap in our knowledge. The chapter reveals how hippopotamus populations can increase rapidly and expand their range even in a context of considerable climatic variability and against a background of deteriorating habitat conditions. Increased anthropogenic activities, especially land-use changes and livestock herding are predicted to adversely affect hippopotamus conservation 16 Chapter 1 efforts, with significant spill over effects on other mammalian grazers dependent on hippo grazing impacts on vegetation along riparian habitats. The ecological implications of hippopotamus grazing and trampling activities and their relations with the environment are covered in Chapters 4 and 5. Although herbivore grazing is an important evolutionary force shaping vegetation biodiversity and structure in African savanna ecosystems, most studies have generalized herbivore grazing effects, with few studying the effects of specific herbivore species, and especially along sensitive riparian habitats. Chapter 4 explores the interactive effects of hippopotamus and livestock grazing on vegetation structure, herbaceous plant species composition and richness along a riparian habitat in protected and pastoral systems of Masai Mara, and demonstrates the important engineering impacts of hippopotamus that enables establishment and co-existence of plant species, culminating in increased species richness in areas experiencing intermediate grazing levels, especially within protected areas. Chapter 5 documents the facilitative role of hippopotamus grazing on habitat use by other wild herbivores along the Mara riparian habitat, demonstrating that hippopotamus grazing activities led to a shifting mosaic of patches that differ in vegetation structure, that enhance structural heterogeneity of vegetation and attract a diverse and abundant herbivore assemblage at intermediate distances from rivers. Lastly, chapter 6 synthesizes the results from chapters 2 to 5 and concludes that hippopotamus are keystone ecosystem engineers able to profoundly modify ecosystems and facilitate other herbivores in the Mara River Basin but the future of their conservation is threatened by dramatic land use changes in the basin, water abstraction from the Mara River, and rising levels of conflict with people throughout Kenyan wetlands. This chapter recommends urgent preparation of a species management plan for Kenyan hippos that aims to reduce human-hippo conflicts and promote peaceful interactions between hippos and local communities. I have tried to make these chapters as independent of each other as possible so that each can be read essentially independently of the others, while retaining a sequence from the very general to the very particular, in what I consider to be a natural order for this thesis. Introduction 17 Chapter two 2 Human-hippo conflicts in Kenya during 1997–2008: Vulnerability of a megaherbivore to anthropogenic land use changes Erustus M. Kanga, Joseph O. Ogutu, Hans-Peter Piepho and Han Olff Published in Land Use Science (2011), DOI: 10.1080/1747423X.2011.590235 Abstract Rising human population and the associated demand for more land, water and other natural resources is intensifying conflicts between people and wildlife worldwide. We investigated the nature, intensity, seasonality, spatial and temporal patterns in human-hippo conflict incidences reported from wildlife stations Kenya-wide, over a 12-year period spanning 1997 to 2008. Overall, 4493 human-hippo conflict incidences were recorded, representing a mean rate of 4.46±0.29 incidences per month. The conflict incidences increased by 1285% from 1997 to 2008, resulting in 937 peak incidences reported in 2008. Number of conflict incidences differed among conservation regions, with incidences increasing during severe droughts and over time. Crop damage was the most commonly reported type of conflict. Wildlife managers attended to 90% of all reported conflict incidences. Hippo mortality increased linearly with increasing conflict incidences, portending a precarious future for hippos outside protected areas of Kenya. This dramatic rise in human-hippo conflicts is a consequence of fundamental land use changes around wetlands and riparian-edge habitats. 20 Chapter 2 Introduction Human population growth and demand for more land, water and other natural resources are intensifying conflicts between people and wildlife worldwide (IUCN 2003). Human-wildlife conflicts (HWC) arise from direct and indirect negative interactions, leading to economic losses to agriculture through destruction of crops, human fatalities and injuries, depredation of livestock and retaliatory killings of wildlife (Hill 1997; Siex and Struhsaker 1999; Tourenq et al. 2001; Treves and Karanth 2003). In the African savannas, intensification of land conversion to cultivation and/or human settlement is a key factor driving people into more direct contacts with wildlife (Sala et al. 2000; Thuiller et al. 2006). The pattern of increasing conflicts between people and wildlife is evident in Kenya (Musau and Strum 1984; Mizutani 1993; Thouless 1994; Kiiru 1995; Sitati et al. 2003; Patterson et al. 2004). Land use changes especially within the pastoral systems of Kenya, driven by rapid expansion of cultivation, land subdivision and privatization of land tenure (Kimani and Pickard 1998; Lamprey and Reid 2004; Okello and D’Amour 2008), are largely responsible for the escalating human wildlife conflicts. As a result, expanding settlements and cultivation are exerting increasing impacts on the distribution and abundance of wildlife at both the population and community levels (Verlinden 1997; Prins 1992; Serneels and Lambin 2001). Consequently, wildlife grazing areas are increasingly dwindling in size, migration corridors are being lost or modified and wildlife access to water sources is getting increasingly blocked, resulting in elevated human wildlife conflicts and wildlife population declines (Serneels and Lambin 2001; Thuiller et al. 2006). The information required to understand and potentially to mitigate these conflicts has not been adequately collated and analyzed in Kenya, especially for the common hippopotamus (Hippopotamus amphibius Linnaeus 1758), except for an unpublished thesis on the Lake Victoria Basin (Post 2000). Megaherbivores (weighing over 1000 kg, Owen-Smith 1988), such as hippopotamus, Elephant (Loxodonta africana Blumenbach 1797), and large carnivores rank among the most problematic and lie at the heart of human wildlife conflicts because they are dangerous to humans. Despite the fact that megaherbivores often cause major devastation to crops and are often a physical threat to humans, most research has focused only on the elephant and neglected hippopotamus, yet the latter are involved in numerous conflicts with people in many parts of Africa (Mkanda and Kumchedwa 1997; Eltringham 1999). Nonetheless, substantial information on human-hippo conflicts is scattered in office files and thus less widely accessible. Hippos differ from other megaherbivores in having a dual requirement of daily living space in water and an open grazing range often visited at night (Eltringham 1999). This requirement affects the manner in which hippos utilize resources and Human-hippo conflicts 21 survive in areas dominated by high human population densities and continuous land use changes. While most studies on human wildlife conflicts have concluded that conflicts are intense on the periphery of protected areas (Naughton-Treves 1998; Saj et al. 2001), this may not necessarily be true for hippos since they inhabit wetlands that often extend outside protected areas into agricultural landscapes. Being mainly wild grazers (Cerling et al. 2008), hippos destroy crops cultivated close to wetlands (Mkanda and Kumchedwa 1997; Eltringham 1999) and pose physical threats to local communities. However, like most other hippo-range states in Africa, Kenya has done little to evaluate the type, extent and consequences of human-hippo conflicts, even though local communities report numerous complaints on hippo damages regularly. Substantial human-induced environmental changes pose a serious challenge to biodiversity conservation (Cincotta et al. 2000; Thaxton 2007). It is probable that significant proportions of threatened and vulnerable species of conservation concern, like the common hippopotamus (Lewison and Oliver 2008), rely on or utilise agricultural landscapes and experience conflicts with humans (Siex and Struhsaker 1999; O’Connell-Rodwell et al. 2000; Tourenq et al. 2001; Green et al. 2005). Therefore, to effectively address human wildlife conflicts, it is necessary to consider both the effects of damage caused by wildlife as well as the impacts of mitigating actions on the conservation status of target species. We thus investigated the nature, intensity, seasonality, spatial and temporal patterns in humanhippo conflicts over a 12-year period spanning 1997 to 2008, to inform decisions on best-practice management of human-hippo conflicts in Kenya. We also attempted to establish correlates of the patterns in human-hippo conflicts, using human-wildlife conflict data collected from a network of 69 wildlife stations and 23 outposts, and interpret the implications of our findings for hippo conservation and management, in the wake of rising human population pressure on wetland habitats across Kenya. Materials and Methods Study area The Republic of Kenya (East Africa) lies between latitude 4° N to 4° S and longitude 34° E to 41° E, with the equator running approximately through the middle of the country. The country covers an area of about 582,646 km2, 8.2% of which comprise 22 terrestrial national parks, 4 marine national parks, 28 terrestrial national reserves, 6 marine national reserves and 5 national sanctuaries administered by the Kenya Wildlife Service. Generally, Kenya’s landuse is largely pastoral in semi-arid zones and agricultural in the moist and humid zones. Rainfall is bimodal in most parts of the country, with short rains normally occurring during October-December and the long rains during March-June. Kenya experienced extreme El Niño floods 22 Chapter 2 N 300 km Figure 2.1 Map of Kenya, showing conservation regions, protected areas and KWS stations that reported human-hippo conflicts during 1997–2008. in 1997–1998, mild El Niño floods in 2001–2004 and 2007, and severe droughts in 1999–2000, 2005–2006 (Ogutu et al. 2007) and in 2008–2009. Human population size in Kenya grew rapidly during the past half century, from 8 million in the 1960s to about 37 million by 2007, at an average annual rate of 2.8% (CBS 2001; Thaxton 2007); an increase associated with rising demand for more land for settlements and cultivation, with increased contacts between people and wildlife, especially close to water sources (UNEP 2009). The Kenya Wildlife Service mandate is to conserve and manage wildlife in Kenya, and has therefore stratified the country geographically into Conservation Regions (Figure 2.1), based on broad ecosystems and landscape characteristics for ease of biodiversity conservation administration. Wetlands, the main hippopotamus habitats, cover about 2–3% of the country’s surface area and support a substantial proportion of the Kenya’s biodiversity resources. These wetlands are diverse in type and distribution but face numerous threats, including pollution, cultivation, Human-hippo conflicts 23 reclamation for settlements and unsustainable exploitation (Crafter, Njuguna and Howard 1992). Conversion of wetlands to agriculture and the impact of farming on riparian habitats are the main threats to hippopotamus conservation in Kenya, followed by illegal poaching for meat and their canine teeth ivory (Weiler, DeMeulenaer and Vanden-Block 1994; Williamson 2004). Although hippo population numbers are known to be declining in most parts of Africa, comparable information on hippo population trends is still lacking for Kenya (Eltringham 1999; Lewison and Oliver 2008; Kanga et al. 2011), despite the fact that human encroachment on wetlands has greatly interfered with hippopotamus ecology and heightened humanhippo conflicts Kenya-wide. Methods We collated information on human-hippo conflict incidences from Occurrence Books in which human-wildlife conflict incidences were recorded daily at 69 wildlife stations and 23 wildlife outposts Kenya-wide during 1997-2008. Records in the Occurrence Books are made whenever members of the public reported complaints or Kenya Wildlife Service personnel make field visits in response to communities’ distress calls. Conflicts were grouped into crop damage, human mortality and injury, livestock mortality, hippo mortality and physical threat categories. Conflict incidences that could not be assigned to any of these five categories were lumped together as unclassified. Physical threats denoted incidences where hippos intruded on people, threatened their safety or constrained their free movements. Statistical data analysis We first stratified the conflicts dataset geographically by conservation regions and then modelled temporal trends in the number of conflict incidences reported for each region per year using the zero-inflated negative binomial regression, assuming a negative binomial distribution of conflict incidences. The aim of this modelling was to smooth climate related inter-annual fluctuations in order to understand seasonal and long term trends over the study period. Further, we modeled temporal trends in the expected monthly frequencies of conflict incidences in each region over the 12-year period and accounted for seasonality, using a quadratic month effect, and regional differences in the incidences. The zero-inflated model was selected to account for excess or structural zeros in the data arising potentially from underreporting of actual conflict incidences or random zeros corresponding to zeros expected under the negative binomial probability model. We first established that the data were over-dispersed relative to the Poisson distribution, a baseline model for count data, and that the zero-inflated negative binomial model gave a better fit to the conflict incidences than the zero-inflated Poisson model using the Vuong test (Vuong, 1989). We also compared the mean number of conflict incidences 24 Chapter 2 per station per year and per station per month among regions using one-way ANOVA. We regressed the number of conflict incidences summed over all regions on year and accounted for serial autocorrelation of error terms using the first-order autoregressive model. However, the model with serial autocorrelation had weaker support in the data than a model assuming complete independence based on the Akaike Information Criterion (Burnham and Anderson 2002), which we therefore used for final inference. Finally, we used the negative binomial regression model to relate hippopotamus mortality to the level of conflict incidences in Kenya. All models were fitted in STATA (StataCorp 2001). Results Temporal patterns in conflict incidences A total of 4493 human-hippo conflict incidences were reported between 1997 and 2008, corresponding to a mean rate of 4.46±0.29 (1SD) incidences per month. The highest number of conflict incidences reported per year was 937 in 2008, representing an increase of 1285% from 41 incidences reported for 1997. Conflict incidences were initially low until the severe drought of 1999–2000 after which the incidences rose markedly to over 400 per annum during 2000–2002. Thereafter, the number of incidences dropped by more than a half during the high rainfall period of 2003–2004. The conflict incidences began to rise again, albeit more gradually during the severe drought of 2005–2006, and were distinctly higher than expected in the drought of 2008. Marked increases in conflict incidences were thus contemporaneous with severe droughts and conflicts increased significantly linearly over time (Figure 2.2, LN(conflicts) = –420.86 +0.213 × year, p = 0.008). 7.0 R2 = 0.476 6.5 LN (conflicts) 6.0 5.5 5.0 4.5 4.0 3.5 1996 1998 2000 2002 2004 2006 2008 year Figure 2.2 Trends in human-hippo conflicts in Kenya during 1997–2008 (Upward pointing arrows indicate dry while downward pointing arrows indicate wet periods). Human-hippo conflicts 25 A B 5 Coast 4 3 2 1 Central 0 3 2 1 0 4 Southern 3 2 0 4 Mountain LN (conflicts + 1) 1 3 2 1 0 3 Tsavo 2 1 Northern 0 3 2 1 0 5 Western 4 3 2 1 0 1996 1998 2000 2002 year 2004 2006 2008 1 2 3 4 5 6 7 8 9 10 11 12 month Figure 2.3 Long-term (A) and seasonal (B) trends in human-hippo conflicts in Kenya during 1997–2008. 26 Chapter 2 The expected conflict incidences differed significantly among conservation regions (Z = –4.52, p < 0.001), with a significant increase in conflict incidences over time evident in the Coast (Z = 3.68, p < 0.001), Central Rift (Z = 2.29, p = 0.022), Southern (Z = 2.46, p = 0.024) and Tsavo (Z = 2.72, p = 0.007, Figure 2.3) regions. Frequency distribution of conflict incidences by region The Coast region contributed the highest number of conflict incidences (46%), followed by Western (19%), Southern (12%), Tsavo (10%), Mountain (6%), Central Rift (5%), and Northern (2%) regions (Table 2.1). Multiple pairwise comparisons of mean conflict incidences per station per year and per station per month across regions revealed significant regional distinctions (F6, 6617 = 51.9, p < 0.001, Table 2.2). Table 2.1 Summary of descriptive statistics of monthly human-hippo conflict incidences in Kenya during 1997–2008. STD =1 standard deviation; IQR = Interquartile range; N= Total number of months; TS= Total number of all KWS stations; CS=Number of stations that recorded conflicts. Region Mean STD Median IQR Min Max N TS CS Coast 14.2 17.9 6.5 23.5 0 91 144 14 6 Western 5.7 9.0 2 8.5 0 71 144 11 7 Southern 3.9 6.7 1 5 0 32 144 7 6 Tsavo 3.0 4.1 1 5 0 20 144 7 3 Mountain 2.0 3.7 1 2 0 29 144 9 6 Central Rift 1.7 2.8 0 2 0 13 144 11 10 Northern 0.73 1.4 0 1 0 9 144 11 8 Table 2.2 Mean number of human-hippo conflict incidences per station per year and per station per month in each conservation region in Kenya during 1997–2008, and pairwise comparisons of regional differences. N1 is the number of stations times the number of years and N2 is the number of stations times the number of months in the period 1997–2008.. Conservation Region Station and year Station and month Mean SE N1 Mean† SE N2 2.03 0.48 120 0.17 a 0.02 1440 28.01 8.62 72 2.33 d 0.26 864 Mountain 3.81 0.89 72 0.32 abc 0.04 864 Northern 0.95 0.27 96 0.08 ab 0.01 1152 Southern 7.72 2.93 72 0.64 c e 0.09 864 11.92 4.01 36 0.99 e 0.13 432 9.77 2.31 84 0.81 e 0.09 1008 Central Rift Coast Tsavo Western †Means with similar letters were not significantly different at P = 0.05 Human-hippo conflicts 27 Frequency distribution of conflict incidences by type The most widely reported type of hippo conflict was crop damage (62.1%), followed by physical threat (15.0%), hippo mortalities (13.3%), human fatality and injury (3.4%), and livestock mortality (1.1%). The remaining 5.1% were unclassified conflict reports. The 745 conflict incidences reported in 2008 and involving both crop damage and physical threats suggest that land use changes within hippopotamus habitats had elevated conflict incidences by 2,659% relative to 27 incidences reported in 1997. The temporal distributions of crop damage also varied considerably among regions and accounted for 50, 18, 12, 9, 6, 3 and 3% of all the incidences reported for the Coast; Western; Southern; Tsavo; Mountain; Central Rift and Northern regions, respectively. Seasonality in conflict incidences There was a significant difference in expected monthly conflict incidences among regions (Z = 4.73, p < 0.001), implying that the impact of human land use practices on hippos differed regionally. However, conflict incidences were seasonal in most regions with a peak generally evident during June-August (Figure 2.3). The seasonality in conflict incidences was significant for the Coast, Mountain, Southern and Western regions (Table 2.3), and was influenced strongly by seasonal variation in crop damage that accounted for 63% of all the conflict incidences, consistent with reports that hippos ate and trampled on a variety of crops. Relationship between conflict incidences and hippo mortality Hippo mortalities increased significantly linearly with increasing number of reported conflicts (R2 = 0.736, Z = 11.90, p < 0.001), implying that elimination of individual animals at conflict points through problem animal control is a major cause of hippo deaths in Kenya. On average, Kenya Wildlife Service attended to 90% of human-hippo conflict incidences over the 12-year period, including 93, 84, 70, 89, 89, 92, 87, 94, 94, 98 and 95% of all reported incidences each year from 1997 to 2008, respectively. Discussion This study revealed four distinct patterns in the spatial and temporal distribution of human-hippo conflict incidences in Kenya. First, conflicts occurred throughout the year but with a seasonal peak apparent during the transition from the late-wet (May-June) to the early-dry (June-August) season, a period of crop ripening in most parts of the country. Second, although conflict incidences occurred in all conservation regions, there was an apparently higher concentration of incidences in the Coast (46%) and Western (19%) regions. Third, about 63% of human-hippo conflicts 28 Chapter 2 Table 2.3 Results of analyses of monthly variation (seasonality) in human-hippo conflicts across conservation regions in Kenya during 1997–2008. Conservation Region Effect Coast Intercept Month Mountain 6.15 <0.001 3.14 0.002 –3.31 0.001 Intercept 0.81 0.52 1.57 0.117 Month 0.23 0.18 1.32 0.187 Month × Month –0.02 0.01 –1.88 0.060 Intercept –0.60 0.44 –1.36 0.172 0.41 0.16 2.53 0.011 Month × Month –0.02 0.01 –1.86 0.063 Intercept –0.83 0.52 –1.59 0.113 0.32 0.19 1.65 0.098 –0.03 0.02 –1.77 0.077 0.27 0.49 0.56 0.573 Intercept Month Month × Month Intercept 0.56 0.19 2.97 0.003 –0.04 0.01 –2.96 0.003 2.07 0.40 5.2 –0.19 0.14 –1.38 0.169 Month × Month 0.01 0.01 1.28 0.202 Intercept 0.86 0.40 2.16 0.031 Month 0.37 0.14 2.66 0.008 –0.02 0.01 –2.18 0.029 Month Western 0.34 0.01 Month × Month Tsavo 2.12 0.12 Month Southern Z 0.36 Month Northern P >|Z| SE –0.03 Month × Month Central Rift Estimate Month × Month <0.001 in Kenya arose from agricultural- related causes (i.e. crop damage and livestock mortalities). Lastly, about 78% of the conflict incidences (agricultural and physical threats) are associated with human-induced land use changes. The management responses to these conflicts led to considerable losses of hippos annually through problem animal control responses. The dramatic rise in human-hippo conflicts across Kenya is a consequence of both natural and human-mediated disturbances of wildlife habitats (Lamprey and Reid 2004), including wetlands (Crafter et al. 1992). The high conflict incidences recorded during 2001–2002 may have been largely influenced by the 1999–2000 drought while the high incidences during 2007-2008 can be attributed to the effects of both drought and land use changes that continued to perturb hippopotamus habitats. The scale and distribution of conflict incidences varied between conservation regions, underlining regional differences in land use patterns. Conflicts were Human-hippo conflicts 29 high in regions where hippopotamus coexists with high human population densities, particularly in close proximity to major wetlands and rivers. This was true for the Coastal and Western regions, characterized by high human populations, practicing subsistence crop farming mostly on wetlands and river banks, unlike in the Northern region where pastoralism is the main economic activity, with minimal or no crop cultivation (UNEP 2009). Human-hippo conflicts occurred throughout the year in all areas but showed an overall seasonal pattern, with an annual peak generally during June-August, a period of crop ripening in most parts of the country. This pattern is consistent with the observation that over 63% of all the conflict incidences were related to agriculture and is similar to that reported for Malawian hippos (Mkanda and Kumchedwa 1997). The probable proximate causes of the observed pattern of human-hippo conflict are linked to increasing human population and the associated increase in demand for agricultural and settlement space, especially in areas close to water, and the fact that hippos, humans and their livestock compete for resources along wetland margins. In addition, drought and competition with livestock may be forcing hippos to forage further from their daily living space (Field 1970; Lock 1972), increasing their probability of contacts with humans. However, it remains unclear whether the seasonality we observed in hippo conflict incidences reflects seasonal restrictions in food availability or is simply an opportunistic response to greater availability of an alternative, more nutritious and easily accessible food type (Cerling et al. 2008). Similar to other wildlife species, hippos caused serious socio-economic losses to rural Kenyan farmers through crop raids, human mortalities and physical injuries (Mizutani 1993; Butler 2000; Patterson et al. 2004). However, the large number and increasing incidences of crop damage and physical threats posed by hippos in Kenya imply possibly greater economic and social consequences to the livelihoods of affected communities than those caused by other megaherbivores. These consequences are however confounded by the fact that rural communities are increasingly using wetlands for multiple cropping agriculture for subsistence and that such crops are more vulnerable to wildlife damage, especially hippopotamus. The hippopotamus mortalities recorded were highly correlated with the rise in conflict incidences, portending a bleak future for hippos outside protected areas, especially given that no actions are currently being undertaken to stem their persecution. Moreover, actual hippo mortalities could have been higher than reported if injured hippos wandered off and died later. When faced with increased humanwildlife conflicts in Kenya, wildlife managers commonly react by killing the offending animals as a problem animal control measure, in the hope of eliminating the problem animals. Hippopotamus are easy target in wetlands for such control measures. Thus, unregulated problem animal control can adversely affect their population status in the long-term, given that there are likely many unrecorded 30 Chapter 2 incidences of systematic poaching of hippos, further aggravating their plight in Kenya. Conclusions and recommendations Conflicts between people and hippopotamus in Kenya probably cannot be entirely eliminated but can be mitigated, by discouraging agricultural activities in areas with high human densities on lands bordering riparian habitats and promoting sustainable use of wetlands, including through wildlife conservation, with the overall goal of enhancing human wellbeing. Although hippos cause serious damage to crops and physically threaten people, their continued persecution through unregulated problem animal control will drastically reduce their population abundance. If this trend continues unchecked and the conflicts are not well managed, hippopotamus populations in unprotected lands in Kenya may soon become unviable. Human-hippo conflicts could be reduced through effective public education, promotion of communal conservancies that provide tourism revenues and land rents directly to communities, selective problem animal control programs and translocation of hippo populations in intensively farmed areas. However, given the rapidly expanding human population and frequent food shortages linked to recurrent droughts in Kenya and the fact that riparian-edge areas are often some of the best for agriculture, successfully balancing the need for national food security and conservation of hippos will undoubtedly require considerable ingenuity and resources. A Kenya-wide distribution and status survey for hippopotamus is needed as a basis for developing effective management and conservation interventions for hippos outside protected areas. Acknowledgements We thank Walter Mususi and Moses Maloba for assistance with the collation of the conflicts dataset. We also thank the Kenya Wildlife Service for logistical support and for availing the conflict data. EK was supported by the Netherlands Fellowship Program (NFP) and the University of Groningen through the Government of Kenya and by the Frankfurt Zoological Society (FZS). Human-hippo conflicts 31 Chapter three 3 Population trend and distribution of the Vulnerable common hippopotamus Hippopotamus amphibius in the Mara Region of Kenya Erustus M. Kanga, Joseph O. Ogutu, Han Olff and Peter Santema Published in Oryx (2011) 45: 20-27 Abstract The common hippopotamus Hippopotamus amphibius can significantly influence the dynamics of ecosystems and engender serious conflicts with people but, in Kenya, one of the species strongholds, it has been little studied or monitored. We surveyed the hippopotamus population in the Masai Mara National Reserve and the adjoining pastoral ranches in 2006 using foot counts along 155.3 km of the main rivers. We counted 4,170 hippopotamuses in 171 schools. Comparisons with earlier surveys suggest that this population increased by 169.6% between 1971 and 1980 within the reserve and, although it did not increase within the reserve during 1980–2006, it increased by 359.4% outside the reserve during this period against a background of deteriorating habitat conditions. The overall density in 2006 was 26.9 hippopotamuses per km of river, equivalent to a biomass of 26,677 kg/km of river. The ratio of calves to 100 adults was 9:100 inside the reserve, 10:100 outside the reserve and 6:100 along tributaries of the Mara River, implying that the population is either increasing or that its spatial distribution is being compressed because of range contraction. The apparent increase in the hippopotamus population contrasts with marked contemporaneous declines in the populations of most other large mammalian herbivore species in the Reserve. We discuss possible reasons underlying the increase in the hippopotamus population. 34 Chapter 3 Introduction The common hippopotamus Hippopotamus amphibius is a semi-aquatic artiodactyl of sub-Saharan Africa (Kingdon 1979; Eltringham 1999) and, historically, was widely distributed throughout the region (Eltringham 1999; Feldhake 2005; Lewison and Oliver 2008). Five evolutionary units have been described based on morphological differences (Ansell 1971; Grubb 1993; Eltringham 1999) but only three of these are genetically different (Okello et al. 2005). The range of the hippopotamus has become increasingly restricted in recent decades, a contraction that has been accompanied by substantial declines in abundance, with the most recent estimates suggesting population declines of 7–20% during 1996–2004 (Eltringham 1999; Lewison and Oliver 2008). Although the causes of these declines are documented and well understood (habitat loss, exploitation and conflicts with people), they continue to operate and appear unlikely to be eliminated in the near future, amplifying the need to develop effective conservation measures for the hippopotamus. Recent estimates suggest that 125,000–148,000 hippopotamuses currently occur in fragmented populations in rivers, lakes and other wetlands of eastern, western and southern Africa (Oliver 1993; Lewison and Oliver 2008). Of the 36 countries where the common hippopotamus is known to occur, 20 have confirmed declining populations, seven have populations of unknown status, nine have stable populations and three (Algeria, Egypt and Mauritania) have experienced recent extinctions (Lewison and Oliver 2008). Based on the estimated global population, coupled with intensifying threats of poaching for meat and ivory (Weiller et al. 1994; Williamson 2004; Conservation 2006), progressive habitat loss and persecution because of conflicts with people, the hippopotamus was categorized as Vulner-able on the IUCN Red List in 2006 (Lewison and Oliver 2008). Despite its Vulnerable status and ecological significance, and rising conflicts with people, the hippopotamus has not been well studied or monitored in many parts of its range, including Kenya where the species has been officially protected since the 1920s (Kenya Game Department, 1953). Monitoring is necessary to understand the factors underpinning population dynamics and hence to develop an understanding of how the hippopotamus influences, and is influenced by, changes in riparian habitats (Field 1970; Thornton 1971; Lock 1972; Eltringham 1999) and responds to land-use changes, climate change and variability, and conflicts with humans. The paucity of data on hippopotamus population status and dynamics in Kenya is due in part to the difficulty and high costs of counting a nocturnal, semiaquatic mammal inhabiting river systems that are often fringed by dense riparian woodlands. It is this difficulty that has primarily limited hippopotamus population monitoring in the Mara Region of Kenya, where regular aerial monitoring and occasional ground counts of other herbivores have been conducted over the last 3 Hippopotamus in the Mara region 35 decades (Stelfox et al. 1986; Broten and Said 1995; Ottichilo et al. 2000; Homewood et al. 2001; Serneels et al. 2001a; Reid et al. 2003; Ogutu et al. 2009). Hippopotamuses were counted only five times in the Masai Mara River systems between 1958 and 2006 compared to 50 times for the other large herbivores of the Mara Region (Talbot and Stewart 1964; Ottichilo et al. 2000; Ogutu et al. 2009; Kenya Wildlife Service, unpubl. data; Department of Resource Surveys and Remote Sensing of Kenya, unpubl. data). These counts reveal important patterns of temporal variation in the population abundance of the hippopotamus in the area and emphasize its importance for the dynamics of the Serengeti-Mara ecosystem (Darling 1961; Olivier and Laurie 1974; Karstad 1984; Reid et al. 2003). Our objectives in this study were to establish the current status of the hippopotamus population in the Mara Region and to investigate how the population has changed both spatially and temporally. We present data on hippopotamus population abundance in the Mara Region since 1971, and compare the temporal patterns to those of sympatric megaherbivores (elephant Loxodonta africana, black rhino Diceros bicornis and giraffe Giraffa camelopardalis) over the same period. We evaluate the effects of land use on this hippopotamus population and examine the implications of continuing changes in land use on the conservation and management of the species in the Serengeti-Mara ecosystem. Study area The Mara Region in south-west Kenya is bounded by the Serengeti National Park in Tanzania to the south and the Siria escarpment to the west (Fig. 3.1). This region forms the northernmost limit of the Serengeti-Mara ecosystem straddling the Kenya-Tanzania boundary. The ecosystem comprises several wildlife conservation administrations and conservation-pastoralist multiple land-use zones in the two countries (Sinclair and Arcese 1995). The 5,500 km2 Mara includes the c. 1,530 km2 Masai Mara National Reserve and the adjacent pastoral ranches of Koyiaki, Olkinyei, Siana, Lemek and Ol Chorro Oiroua with a combined total of 4,000 km2. The Mara receives a mean total annual rainfall of 600 mm in the south-east rising to 1,200 mm in the north-west (Norton-Griffiths et al. 1975). Rainfall is bimodal, with the short rains falling during November-December and the long rains during January-June, although January and February are often dry. The vegetation is predominantly grassland, with isolated scrublands and woodlands, especially along drainage lines and on hilltops (Epp and Agatsiva 1980). Several rivers and numerous streams drain the Mara but the Mara River, traversing both Kenya and Tanzania, is the only river that flows all year. The Sand, Talek and Olare Orok rivers are the main tributaries of the Mara River and are largely seasonal. The Mara River is 396 km long and its flow through the Masai 36 Chapter 3 Ethiopia N ua ro Kenya Somalia Uganda Sudan rro ho Oi Lemek C Ol rok river Nairobi Olkinyei Mare river Olare-O Tanzania Se ren get iN Talek river MMNR Sa atio nal river system international border Koyiaki Pa rk, Tan z nd Siana rive Keekorok Pool r ani a Masai Mara National Reserve 20 km Figure 3.1 Masai Mara National Reserve and the adjoining pastoral ranches, showing the Mara River and its tributaries. Mara National Reserve and Serengeti National Park sustains a large variety of abundant wildlife, including hippopotamus, crocodile Crocodylus niloticus, wildebeest Connochaetes taurinus, Burchell’s zebra Equus burchelli and Thomson’s gazelle Gazella thomsoni. This wildlife assemblage supports a robust tourism industry in the Mara. However, wildlife populations there are facing many waterrelated problems, including increasing water shortages and declining water quality linked to expanding irrigated cultivation, unregulated water extraction, and deforestation of the Mau Forest catchments of the Mara River (Mutie et al. 2005). Marked declines in herbivore numbers in the Mara have been attributed to their progressive exclusion from pastoral ranches by land-use changes, including expansion of mechanized and subsistence agriculture and settlements, which have affected 8% of the Mara and caused land cover changes on up to 36% of the adjoining pastoral ranches (Homewood et al. 2001; Serneels et al. 2001b; Lamprey and Reid 2004; Mutie et al. 2005). These changes have probably intensified competition between livestock and wild herbivores on the pastoral ranches of the Mara. Hippopotamus in the Mara region 37 Moreover, settlement of the formerly semi-nomadic Masai pastoralists (Kimani and Pickard 1998; Western et al. 2009) and the associated intensification of land use and grazing by large numbers of livestock on the pastoral ranches has accelerated range degradation and fragmentation, including along riparian habitats. Rising temperatures and recurrent droughts (Ogutu et al. 2007) have amplified herbivore mortalities in the Serengeti-Mara ecosystem. Methods Ground, boat and aerial survey methods have been used to count hippopotamuses (Petrides and Swank 1965; Olivier and Laurie 1974; Marshall and Sayer 1976; Viljoen 1980; Karstad 1984; Tembo 1987; Norton 1988; Smart 1990; Bhima 1996) but accurate counts have been obtained only with ground surveys (Tembo 1987; TAWIRI 2001). We conducted ground counts of hippopotamus along the Mara River of Kenya, its three main tributaries and one major water pool during September–November 2006. This period was chosen because it spans the late dry season when water levels in the rivers are lowest and visibility of hippopotamuses in the water is highest. We divided the study area into river sections using a 1:50,000 map. Three observers walked quietly along the river banks and, upon sighting individuals or groups of hippopotamuses, recorded the total number, group size and number of calves, with the aid of binoculars. We distinguished calves by their small body size relative to adults and subadults. We assumed that the number of individuals counted in a group accurately represented the size of the group, based on calibration trials conducted at the Keekorok Pool with a known number of hippopotamuses. Locations of all individuals and groups were determined with a global positioning system. We tested for differences in expected group sizes between regions of the Mara River within the Masai Mara National Reserve, pastoral ranches, and Mara River tributaries within the Reserve using a negative binomial regression model assuming a negative binomial error distribution and log link function (Edwards and Berry 1987). We performed multiple pair wise comparisons of expected group sizes between regions and used simulation adjustment for multiplicity. We synthesized the denominator degrees of freedom for Wald F-tests using Kenward and Roger’s (1997) method for small sample sizes. All models were fitted with the SAS procedure GLIMMIX (SAS Institute 2006). To compare the expected percentage composition of calves inside and outside the Reserve as well as in the tributaries, we used a logistic regression assuming binomial error distribution and a logit link function. We conducted multiple comparisons of the expected percentage composition of calves across regions and adjusted the tests for multiplicity using simulation adjust- 38 Chapter 3 ment. We used a χ2 goodness-of-fit test to examine differences in hippopotamus densities between regions and years and analyzed temporal trends in abundance by computing percentage change in abundance between consecutive counts. Results We counted 4,170 individuals along 155.3 km of the Mara River system and at one pool. As we walked long sections of the same river in a day the chances of double counting, although hard to eliminate entirely, were probably low. Counts made in 1971 (Olivier and Laurie 1974) and 1980 (Karstad 1984) within the Masai Mara National Reserve indicated that the population increased by 169.6% during this time, i.e. a mean annual growth rate of 18.8% (Table 3.1). Between 1980 and 2006 the population did not increase within the reserve but increased outside the reserve by 359.4%. The overall increase of the population in the Mara River inside and outside the reserve combined was 49.9% for this period, i.e. a mean annual growth rate of 3.1%, during which new groups apparently spread upstream to the pastoral Table 3.1 Number of hippopotamuses counted (with percentage increase compared to previous count), km of river surveyed and density of hippopotamus per km of river in the Mara Region (Figs 3.1 and 3.2) between 1971 and 2006. Blank cells indicate absence of surveys. Olivier and Laurie (1974)3 River section No. km Density (km-1) Mara River inside reserve 738 60 12.3 Karstad (1984)1, 4 No. (% increase) km Density (km-1) 53.3 36.1 1,571 (359.4%) 45.7 34.4 Talek River 158 46.1 3.4 Olare Orok River2 490 10.2 48.0 Keekorok Pool2 27 4,170 155.3 (49.9%; Mara River only) 26.9 Total 74.2 24.1 342 50.2 6.8 No. Density (% increase) km (km-1) 1,924 (-3.3%) Mara River outside reserve2 1,990 (169.6%) This study (2006) 2,332 124.4 17.1 1Karstad used both ground and aerial counts and this enabled comparison of his data with ours. groups established after 1982 3Counts made in July and August 1971 4Counts made in August, September and October 1980 2New Hippopotamus in the Mara region 39 A Old Mara Bridge B Mara Safari Club Koyiaki N Masai Mara National Reserve er re riv Lemek Ma Olare-O rok river Ol Chorro Oiroua Ma re riv er iver kr Tale 10 km Koyiaki river junction for Mara and Talek Hippo group size 1–5 6 – 30 Old Mara Bridge 31 – 60 61 – 132 reserve/ranch borders New Mara Bridge MMNR river system Figure 3.2 Spatial distribution of hippopotamus Hippopotamus amphibius in the Masai Mara National Reserve (A) and Pastoral Ranches (B) in 2006. ranches (Fig. 3.2). Our count in 2006 represents a biomass of 26,677 kg/km of river, assuming a unit weight for a hippo of 1,000 kg (Coe et al. 1976). The density of hippopotamuses in 2006 was 36.1 and 34.4 hippos/km of river within and outside the Masai Mara National Reserve, respectively. A χ2 goodnessof-fit test indicated a significant difference in densities between these two stretches of the Mara River (χ23 – 0.0001, P > 0.05) and over time in the Reserve (χ22 – 0.0001, P > 0.05, Table 3.1). We counted 171 groups of 1–132 individuals (Fig. 3.3). Although group sizes appeared large in the Mara River tributaries (95% confidence limits 18.7–42.5 compared to the Mara River within, 20.2–31.7, and outside, 17.3–27.5, the Reserve), differences in group sizes among the three regions were not significant (F2, 168 = 0.73; P = 0.48). The ratio of calves to 100 adults was 9 : 100 (Reserve), 10 : 100 (pastoral ranches) and 6 : 100 (tributaries). Even though the percentage composition of calves was lower for tributaries (95% confidence limits 3–9%), compared to the Reserve (7–10%) or the pastoral ranches (8–10%), logistic regression analysis showed that the expected percentage composition of calves did not differ across regions (F2, 147 = 1.87; P = 0.59) nor were there significant pairwise differences among regions. 40 Chapter 3 Discussion frequency distribution of group sizes (%) The hippopotamus population size reported here represents the minimum number of individuals in the part of the Mara River we surveyed. The estimated apparent annual growth rate is high, and may suggest immigration from outside, but is biologically achievable for the hippopotamus. Similar growth rates have been reported for the hippopotamus in Luangwa River in Zambia (Marshall and Sayer 1976) and Lundi River in Zimbabwe (O’Connor and Campbell 1986). This apparent growth rate could be partially attributed to protection in the Masai Mara National Reserve and the opportunity for range expansion upstream in the Mara River to the pastoral ranches. The hippopotamus typically has an adult male : female ratio of 1 : 1 (Smuts and Whyte 1981), compared to 1 : 2 typical of most large mammals, a gestation period of 8 months (Marshall and Sayer 1976; Smuts and Whyte 1981), which is short given its large body size, and a high fecundity of 0.55 (on average, a mature female hippo can produce a calf every 21.8 months; Laws and Clough 1966; Smuts and Whyte 1981). These factors all contribute to a high potential for rapid population increase when conditions are favorable. The high rate of apparent population growth reinforces the observation that hippopotamus populations are not often limited by diseases or predation but rather by the availability of suitable habitat and forage (O’Connor and Campbell 1986), with the latter being relatively abundant in less disturbed sections of the Mara (Boutton et al. 1988; Onyeanusi 1988). Hippopotamus density increased three-fold in the Masai Mara National Reserve, from 12.3 hippos/km of river in 1971 to 36.1 hippo/km of river in 2006 but with marked differences in densities between regions (Reserve = 36.1, pastoral ranches = 34.4, Talek River 5 3.4 and Olare Orok River = 48.1 hippos/km of river). These 50 Mara River in Reserve (n = 76) Mara River outside Reserve (n = 72) tributaries (n = 23) 40 30 20 10 0 1–5 6–19 20–50 51–70 >70 Hippo group sizes Figure 3.3 Percentage frequency distribution of hippopotamus group sizes in the Mara region in 2006. Hippopotamus in the Mara region 41 densities are likely to vary between seasons; elevated water levels allow groups to spread out as pools enlarge without a corresponding change in the overall hippo density. The estimated density of 36.1 hippo/km of river within the Masai Mara National Reserve is higher than the 20.2 hippos/km reported for Liwonde National Park in Malawi in 1993 (Bhima 1996) and the 21.6 hippo/km reported for Luangwa River in Zambia in 1970 (Marshall and Sayer 1976) but similar to the 39.7 hippos/km of river reported for the Luangwa River in 1983 (Tembo 1987). However, similar direct comparisons with estimates of hippopotamus densities in other water bodies are often complicated by differences in habitat suitability (Olivier and Laurie 1974; Eltringham 1999). The similarities in expected group sizes across regions complicate identification of high-quality hippopotamus habitat; nonetheless, the relatively large group sizes in the tributaries and pastoral ranches may indicate overcrowding because there are few suitable pools (Olivier and Laurie 1974; Klingel 1991; Viljoen 1995) or compression by land-use changes, humans and their livestock. Although we counted at the end of the dry season when most surface water dries out in the Mara and the distribution of hippopotamuses is more restricted, the counts suggest that the Mara River offers more favorable water conditions for hippopotamuses during the dry season compared to its tributaries, as indicated by the moderate group sizes and wider distribution of the groups encountered, suggesting less crowding. However, land-use changes and livestock herding may be adversely affecting hippopotamuses in the section of the Mara River within the pastoral ranches and its tributaries, where hippopotamuses form relatively large groups (Mara River 17.3–31.7; tributaries 18.7–42.5). The ratio of calves to adults represents the apparent juvenile recruitment rate, although not all calves and adults are likely to be counted in any census and some subadults grouped with adults may not have reached breeding age. However, a high calf : adult ratio is not necessarily indicative of a fast growing population because the actual rate of population growth is not only a function of this ratio but also of juvenile and subadult recruitment and mortalities. The observed ratio for the Mara hippopotamuses of 9 : 100 is almost twice the 4.8 : 100 reported for Luangwa River in Zambia in 1983 (Tembo 1987). Although the percentage composition of calves did not differ among regions the tributaries had a noticeably lower ratio, probably because of overcrowding that may depress population growth. The numerical and spatial changes in the Mara hippopotamus population thus suggests the population is expanding but may also indicate increasing concentration of hippopotamuses in the Mara River because of contraction and compression caused by deterioration and truncation of their habitats from human activities. Moreover, if destruction of the Mara River catchments and increasing water extraction has progressively reduced overall water availability in the watershed, 42 Chapter 3 thus increasing the possibility of sighting hippopotamuses and yielding higher counts, then the changes are unlikely to indicate a true population increase. The density of the hippopotamus in the Masai Mara National Reserve in 2006 was similar to that reported for 1980, implying a stable population in the Reserve. But significant population expansion was evident in the pastoral ranches, where hippopotamus density increased five-fold from 6.8 to 34.4 hippos/km of river. Various authors (Sayer and Rakha 1974; Marshall and Sayer 1976; Smuts and Whyte 1981; O’Connor and Campbell 1986) have suggested that improved environmental conditions, most notably above average rainfall, improve conception and subsequent calf survival and recruitment of the hippopotamus through provision of adequate food and suitable shelter, resulting in high population growth. Our results, however, indicate that the Mara hippopotamus population increased against a background of deteriorating habitat conditions related to recurrent droughts, rising temperatures and progressive habitat desiccation (Ogutu et al. 2007), and fundamental land-use changes (Homewood et al. 2001; Serneels et al. 2001a; Lamprey and Reid 2004; Mutie et al. 2005; Ogutu et al. 2009). The observed increase in the hippopotamus population is inconsistent with the contemporaneous declines in the populations of mammalian herbivores weighing less than 1,000 kg in the Mara (Ottichilo et al. 2000; Homewood et al. 2001; Serneels et al. 2001a; Ogutu et al. 2009). Of the three other sympatric megaherbivores (animals weighing 1000 kg, Owen-Smith 1988) in the Mara, only the elephant population has increased (Dublin 1995; Kenya Wildlife Service, unpubl. Data); black rhino and giraffe populations have declined. The increase in elephant numbers has been attributed to an influx of elephants escaping from poachers in the Serengeti from the late 1970s to early 1990s (Dublin and Douglas-Hamilton 1987). The declines in giraffe and rhino populations have been attributed to declining woodland cover (Dublin 1995, Lamprey and Reid 2004), poaching (Walpole et al. 2001), habitat alteration, fragmentation and loss because of privatization of land tenure, expanding settlements, cultivation, and settlement of the formerly semi-nomadic Masai and consequent intensification of land use (Homewood et al. 2001; Serneels et al. 2001a; Ogutu et al. 2009). Displacement of giraffe and rhinos by pastoral livestock in the Mara might also have contributed to the declines (Mukinya 1973; Walpole et al. 2001; Ogutu et al. 2009). The increase of the hippopotamus population on the pastoral ranches of the Mara, although probably reflecting population growth, could also reflect exclusion of hippopotamuses from parts of their former range in the adjacent pastoral areas because of progressive habitat loss and declining water levels in the Mara River. Given that the hippopotamus is a grazer whereas giraffe and black rhinos are browsers and elephant is a mixed grazerbrowser, hippopotamuses could respond differentially to environmental changes compared to other megaherbivores. However, habitat degradation, fragmentation and loss due to land-use change and poaching are unlikely to be the cause of the Hippopotamus in the Mara region 43 increase in hippopotamuses because many other mammalian grazers have declined in the Mara, suggesting that contrasting feeding styles alone are insufficient to account for these differences. It is unlikely that rainfall was responsible for the expansion of the hippopotamus population in the Mara because, despite fluctuating widely, rainfall did not increase consistently between 1971 and 2006 (Ogutu et al. 2007). A potential contributing factor could have been conversion of woodlands into grasslands in the Mara by elephants and fire (Dublin 1995) and humans (Lamprey and Reid 2004) and maintenance of these grasslands by hippopotamuses and other herbivores. Together with protection in the reserve and pastoral ranches this could have offered suitable conditions for hippopotamuses to thrive. However, this does not explain why populations of sympatric herbivores declined concurrently. Given the persistent declines in numbers of the other herbivores, deteriorating habitat conditions and increasing pressure on water and other habitat resources, the high density of the hippopotamus is most likely indicative of range contraction and compression in the Mara. The increase in hippopotamus density in the pastoral ranches suggests these areas play an important role in sustaining the population. However, land-use changes on the ranches and destruction of forests in the Mau catchments of the Mara River will, unless regulated, restrict the distribution of the hippopotamus population, and reduction in the volume and quality of water in the Mara River and its tributaries will lead to a decline in density. This may have significant spillover effects on other mammalian grazers that are dependent on the grazing lawns maintained by hippopotamuses. Regular monitoring of the Mara hippopotamus population is therefore required to improve our understanding of the response of the species to land-use and climate changes. Because the Mara River is transnational, effective management, conservation and monitoring of the hippopotamus in the Serengeti-Mara ecosystem require close collaboration between relevant institutions in Kenya and Tanzania. Acknowledgements We thank Charles Matankory and Sospeter Kiambi for assistance with fieldwork and for arranging field logistics, the Kenya Wildlife Service rangers for providing security during field work, wardens of the Masai Mara National Reserve and the management of the Koyiaki and Lemek pastoral ranches for allowing us unlimited access to these areas, and Dr Richard H. Lamprey for useful discussions that helped improve this article. EK was supported by the Netherlands Fellowship Programme and the University of Groningen, through the Government of Kenya, and by the Frankfurt Zoological Society. 44 Chapter 3 Hippopotamus in the Mara region 45 Chapter four 4 Hippopotamus and livestock grazing near water points: consequences for vegetation cover, plant species richness and composition in an East African Savannah Erustus M. Kanga, Joseph O. Ogutu, Hans-Peter Piepho and Han Olff Abstract Grazing large mammals shape landscape heterogeneity and the composition and structure of vegetation in savannas. The riverine systems of the Masai Mara National Reserve of Kenya are inhabited and grazed by the common hippopotamus all year, which seems to be especially important in vegetation modification. However, Maasai pastoralists inhabiting pastoral rangelands adjoining the Mara reserve have been progressively settling down from a formerly semi-nomadic lifestyle, thus increasing concentration of livestock grazing along the local rivers, potentially altering these effects of hippo on the riparian vegetation. We examined if landscapes grazed predominantly by hippopotamus and livestock differ in vegetation structure, plant species richness and composition along distance from water sources in the wet and dry seasons. We used 25 transects, each 5 km long and having 13 sampling plots each measuring 10 × 10 m2 and radiating from rivers in the reserve (n = 16) and pastoral ranches (n = 9). In each plot, we measured the height and visually estimated the percent cover of grasses, forbs, shrubs and bare ground, plant species composition and richness and grazing intensity. The riverine areas in pastoral ranches were more heavily and homogonously grazed than the reserve. The mean plant species richness was similar in both landscapes but varied in response to spatial gradients in grazing intensity, mostly due to variation in forb and shrub species. By contrast, the plant species composition differed strikingly between the reserve and the ranches, while species similarity indices declined with increasing distance from water, reflecting differential modification of vegetation structure and spatial heterogeneity by gradients in grazing intensity. Intense and sustained grazing shifted vegetation composition towards annuals and invasive weedy species and grasses with short stature that characteristically exclude fires, thus stimulating densification of woody species. Although the precise differences between hippopotamus and livestock grazing were complex and varied with landscape and seasons, impacts of livestock grazing altered plant species composition, the structure and spatial heterogeneity of vegetation and declined less rapidly with increasing distance from water relative to hippopotamus grazing. 48 Chapter 4 Introduction Grazing large herbivores influence and are reciprocally influenced by vegetation, an interaction that shapes landscape heterogeneity, nutrient cycling, vegetation composition, productivity and structure (McNaughton 1985; Eckert and Spencer 1987; Whicker and Detling 1988; Belsky 1992; Ritchie and Tilman 1995; Frank et al. 1998; Olff and Ritchie 1998; Dahlberg 2000; Eccard et al. 2000; Shackleton 2000; Thrash 2000). The impact of grazing on vegetation varies with the species, density, body size and spatial and temporal distribution of mammalian herbivores (Belsky 1983; Bakker 1985; McNaughton 1986; Olff and Ritchie 1998; Ritchie and Olff 1999). Continuous and intense gazing can exert greater negative impacts on vegetation than can intense but periodic grazing that allows sufficient time for vegetation recovery. Traditional pastoralists in East Africa have long been aware of this and thus distributed the impacts of their livestock grazing by moving them periodically between pastures and allowing sufficient time for vegetation recovery from heavy utilization. Such mobility also enabled livestock herds to more efficiently exploit grazing resources distributed unevenly in space and time (Homewood and Rodgers 1991; Oba et al. 2000). Intense herbivore grazing and trampling creates and widens gaps in vegetation, changes species colonization matrix of rangelands and differentially influences vegetation structure and species composition (Whicker and Detling 1988; Fusco et al. 1995; Zerihun and Saleem 2000; Oba et al. 2001; Thrash 2000; Van Wieren and Bakker 2008). Moreover, the effect of grazing on species richness varies regionally with soil productivity (Olff and Ritchie 1998), such that ecosystems with moderate to high soil productivity have higher plant species diversity than those with lower productivity (Olff and Ritchie 1998; Bakker 1998; Milchunas et al. 1988, 1998; Proulx and Mazumder 1998; Bakker et al. 2006). Plant species diversity can be enhanced by low to moderate grazing intensity (Bakker 1989; Van Wieren 1995; Hodgson and Illius 1996) but reduced by high grazing intensity (Milchunas et al. 1988; Hobbs and Huenneke 1992). As a result, moderate disturbances induced by intermediate grazing intensities can support high levels of diversity in grassland communities (Grime 1973; Zeevalking and Fresco 1977; Milchunas et al. 1988; Puerto et al. 1990; Hobbs and Huenneke 1992). Other important consequences of grazing include trampling that enhances creation of niches for colonizing species and propagule dispersal (Olff and Ritchie 1998; Bullock and Marriott 2000; Bakker and Olff 2003). As well, grazing by mixed herds of different herbivore species can enhance vegetation productivity and plant species diversity, with the effect varying depending on the complement of herbivore species involved and the status of resources limiting plant growth, such as water, nutrients and light (Bell 1971; Jefferies et al. 1994; Ritchie at al. 1998; Pausas and Austin 2001). Thus, the effect of grazing on vegetation can be complex and vary with the environment, production system, spatial and temporal scales. Contrasting effects of hippo and livestock grazing 49 Riparian savanna habitats grazed heavily by hippopotamus (Hippopotamus amphibious Linnaeus 1758) or livestock, experience ecological stresses through depletion of herbaceous vegetation and increased denudation which can be detrimental to habitat suitability for other herbivores (Lock 1972; Eltringham 1999; Fleischner 1994; Thrash 2000). Hippopotamuses and livestock sharing the same landscape may compete for grazing resources, especially close to water, differentially modify vegetation structure and produce contrasting impacts on riparian habitats as a result. However, despite grazing being an important evolutionary force shaping vegetation biodiversity and structure in African savanna ecosystems (McNaughton 1979; 1983; 1984; 1988), a comparative evaluation of the effects of hippopotamus and livestock grazing on herbaceous plant species richness and composition in protected and pastoral landscapes has received relatively scanty attention. Consequently, we investigated how grazing by hippopotamus and livestock modify vegetation structure, species richness and composition along distance from water sources in a protected and adjoining pastoral landscapes in the Mara Region of Kenya. We expected hippopotamus to cause fewer patches of bare ground than livestock because of differences in their grazing strategies. Hippopotamus pluck grasses and create patches of short grass lawns whereas livestock pull up shallow-rooted grasses as a result of their bulk-feeding style. We further expected the varying intensity of hippopotamus and livestock grazing to exert differential impacts on vegetation, resulting in differences in vegetation structure, plant species abundance, richness and composition and dominance of particular plant species. More particularly, we expected vegetation height and cover to increase with increasing distance from water sources, due to declining grazing intensity away from water, in both hippopotamus and livestock dominated areas. In contrast, we expected plant species richness to increase with increasing distance from water, owing to declining grazing intensity farther from water, and to be higher in areas grazed predominantly by hippopotamus than by livestock. Finally, we expected both hippopotamus and livestock grazing to encourage the establishment and spread of invasive and annual plant species through competitive release, especially in heavily grazed areas. Testing predictions of these hypotheses is essential to enhancing our understanding of the long-term consequences of the ongoing sedenterization by pastoralists and their livestock on the biodiversity of riparian habitats, and the associated forage resources in savanna rangelands of the Mara and possibly elsewhere. Materials and Methods Study area The Mara Region (Mara) is located in south western Kenya, between latitudes 50 Chapter 4 a o orr Kenya Ol rou Oi Ch N Lemek 20 Nairobi 19 Tanzania 18 Olkinyei 15 24 23 14 21 17 9 25 13 7 11 Koyiaki 22 12 4 10 Se 5 km transects ren 1 get iN atio 5 6 3 2 nal Pa rk, MMNR Tan z ani a 16 Siana Kenya 20 km Figure 4.1 Map of Masai Mara National Reserve and the adjoining pastoral ranches showing the transects (numbered) radiating from rivers, sampled during 2007–2008. The study area encompassed the protected Masai Mara National Reserve and the Koyaki, Lemek and Ol Chorro Oirua pastoral ranches. 34º45´ E and 36º00´ E and is bounded by the Serengeti National Park (SNP) in Tanzania to the south and Siria escarpment to the west (Fig. 4.1). This region forms the northernmost limit of the Serengeti-Mara ecosystem, covering some 25,000 km2 and straddling the Kenya-Tanzania boundary. The ecosystem comprises several wildlife conservation administrations and conservation-pastoralist multiple land use zones in each of the two countries (Sinclair and Arcese 1995). The Mara covers about 5,500 km2, with the Masai Mara National Reserve (MMNR) covering some 1,530 km2 while the adjacent pastoral ranches, including Koyiaki (931 km2), Olkinyei (787 km2), Siana (1316 km2), Lemek (717 km2) and Ol Chorro Oiroua (59 km2) cover a combined total of about 4,000 km2. The Mara receives an annual rainfall of about 600 mm in the south east, rising to about 1300 mm at the north western edge (Norton-Griffiths et al. 1975; Ogutu et al. in press). Rainfall is bimodal, with the short rains falling from November to December and the long Contrasting effects of hippo and livestock grazing 51 140 long term (1990–2005) sample period (2006–2008) mean rainfall (mm) 120 100 80 Figure 4.2 Periodic and seasonal rainfall distribution for the Mara region of Kenya, during the sampling period and long term averages. 60 40 20 0 early dry late dry early wet late wet seasonal periods rains from January to June, though January and February are often dry. During the sampling period, rainfall approximated the multiyear norm (Fig. 4.2). The Mara plains are blanketed by extensive flows of Tertiary phonolitic lava, but dark, nutrient-rich deep clay vertisols, also called black cotton soils, are more extensive (Williams 1964; Glover 1966). The vegetation is predominantly grassland, with isolated scrublands and woodlands, especially along the drainage lines and on hill tops (Epp and Agatsiva 1980). The Mara has had a long history of harmonious coexistence between pastoralists and wildlife dating back to several millennia (Marshall 1990; McCabe 2003). Traditional pastoralism remains the major form of land use to date, and the Mara still supports a robust and diverse assemblage of large herbivores, with livestock numbers having been largely stable between 1977 and 2002 despite marked seasonal fluctuations (Broten and Said 1995; Serneels and Lambin 2001; Lamprey and Reid 2004). However, marked declines by large wild herbivores in the Mara during 1977-2003 have been attributed to progressive exclusion from the pastoral ranches by land use changes, including expansion of large-scale mechanized commercial and small-scale subsistence agriculture and settlements, human population growth, illegal wildlife harvests and marked climatic variability (Homewood et al. 2001; Serneels and Lambin 2001; Ottichilo et al. 2001; Ogutu et al. 2009). These changes progressively degrade, fragment and contract wildlife habitats, thereby intensifying competition between livestock and wild herbivores in the pastoral ranches. Together with land subdivision and privatization of land tenure (Kimani and Prickard 1998) and sedenterization of the formerly semi-nomadic Maasai pastoralists and the associated intensification of land use in Masailands (Western et al. 2009), these processes progressively compress wildlife and livestock distributions and heighten conflicts among the competing and incongruent land uses, including along riparian habitats. 52 Chapter 4 Sampling design We selected two landscapes; a protected conservation reserve, the Masai Mara National Reserve (MMNR), and the adjoining community pastoral ranches of Koyiaki, Lemek and Ol Chorro Oiroua (Fig. 4.1). Livestock grazing is prohibited in the reserve except for illegal incursions but livestock and wildlife graze together in the pastoral ranches. We established 25 random transects, each 5 km long and radiating from the Mara, Talek and Olare Orok Rivers. Sixteen transects were located in areas grazed by hippopotamus and other wild herbivores, while another nine transects were placed in areas grazed by livestock, hippos and other wild herbivores (Fig. 4.1). However, along the 5 km riparian strip, hippos and livestock are the main resident grazers in the MMNR and the pastoral ranches, respectively. Topography increased rather gently away from rivers within the 5 km distance sampled by transects in both the reserve (range 1668 m to 1718 m) and the pastoral ranches (1773 m to 1836 m). Along each transect, we established 13 sampling plots each measuring 10 × 10 m2 at distances of 0, 100, 250, 500, 750, 1000, 1250, 1500, 2000, 2500, 3000, 4000 and 5000 meters from rivers. Because we expected vegetation to change more rapidly close to, than far from rivers, we reduced the intensity of sampling away from rivers to capture this gradient. In each plot, we visually estimated the percent cover of three growth forms of vegetation (grasses, forbs and shrubs) and bare ground. Grasses were further subdivided into three height classes: less than 10 cm tall, 10–30 cm, and greater than 30 cm. The cover measurements provided a simple, quick and efficient method for assessing rangeland conditions. We estimated plant species richness and abundance by identifying and counting individuals of each plant species in each plot. Plant specimens that could not be definitively identified in the field were taken to the East African Herbarium for further identification. Plant nomenclature follows Agnew and Agnew (1994) and Beentje (1994). Additionally, we recorded and scored the intensity of grazing within a radius of 30 m from the centre of each plot. The grazing score was set on a scale of one (heavily grazed) to four (no clear evidence of grazing), based on visual assessment. Finally, because hippopotamus can deplete herbaceous vegetation and increase denudation in areas that they heavily utilize, we counted all hippopotamus trails within a 50 m radius from the center of each plot. Field samplings were carried out during the early dry (July-August) and late dry (September-October) seasons of 2007 and 2008 and in the late wet season (March-April) of 2008. We were unable to access the study area to obtain samples for the early wet (January-February) season of 2008 as scheduled due to the outbreak of widespread post-election violence in Kenya at the time. Transects were treated as the unit of replication. The total of 650 samples (n = 325 plots × 2 seasons) dropped to 634 as 16 samples (n = 8 for the reserve and n = 8 for the ranches) were discarded because the associated plots were either burned in the dry season, or were inaccessible in the wet season due to heavy rainfall. The 16 Contrasting effects of hippo and livestock grazing 53 transects used in the reserve therefore produced 406 samples during the wet and dry seasons combined whereas the 9 transects used in the pastoral ranches produced 228 samples over the same period. Statistical analysis Percentage cover of the five vegetation components and bare ground were arcsine square-root transformed prior to analyses. We then used Mann-Whitney U-test to relate grazing intensity scores to distance from water and landscapes. Further, we used a multivariate general linear model to relate the proportions of bare ground, vegetation cover and species richness to distance from water, landscapes, seasons and their interactions. We calculated the mean frequency of each species at each sampling distance from water per landscape and estimated the contribution of each plant life form to the total species richness between landscapes, seasons and along distance from water. To estimate the proportion of plant species shared between landscapes, we used a simple binary measure of species presence and absence, the Jaccard’s coefficient. This index measures the similarity in species composition between two communities (A and B), as C = j/(a+b-j), where j is the number of species common to both communities and a and b are the numbers of species occurring only in communities A and B, respectively. The index ranges from zero, for two communities with no species in common, to one, for two communities with identical sets of species (Magurran 1988). Lastly, we used gradient analysis to examine plant species compositions between the two landscapes based on species frequency of occurrence along distance from water. First, a Detrended Correspondence Analysis (DCA) was used to determine the length of the gradient, which was 1.3, and therefore a Principal Components Analysis (PCA) was used for further analyses (ter Braak 1985). Preliminary analyses showed that samples from plots on river banks had strong effect on ordination and we therefore removed these samples from our analysis, to show more continuous effects of gradients. We used grazing intensity, number of hippopotamus trails and distance from water as passive environmental variables to correlated species composition along axes. All models were fitted in Statistica (version-8, StatSoft 2007) and in PC-ORD (McCune and Mefford 2006). Results Grazing intensity, distribution of hippopotamus trails and vegetation cover Grazing intensity was higher in the pastoral ranches (mean rank = 397.33, n = 228) than in the MMNR (mean rank = 272.67, n = 406; Mann-Whitney U = 28083, P < 0.001). The intensity of grazing did not change significantly along distance from water in the pastoral ranches (Kendall’s tau_b = -0.069, P > 0.05, Fig. 4.3), but 54 Chapter 4 mean grazing intensity (increasing factor 1–4) 4 3 pastoral ranches 2 1 Masai Mara National Reserve 0 0–0.75 1–2 2–3 Figure 4.3 Mean grazing intensity as a function of distance from water in the Mara region of Kenya during 2007–2008. Solid and dashed lines denote the Masai Mara National Reserve and pastoral ranches, respectively. 4–5 distance from water (km) declined significantly with distance from water in the MMNR (Kendall’s tau_b = -0.401, P < 0.001, Fig. 4.3). The mean number of hippopotamus trails was significantly higher in the MMNR (F1, 618 = 17.6, P < 0.001; 0.31±0.02, n = 406) than in the pastoral ranches (0.14±0.01, n = 228) and declined significantly with distance from rivers (F3, 618 = 36.2, P < 0.001), with the decline being steeper for the MMNR (P = 0.013). Hippopotamus actively utilized a strip within 2.5 km on either side of the rivers in both landscapes, and this strip was patchily grazed in the MMNR. The mean percentage cover of the five components of vegetation differed significantly across seasons (F6, 616 = 11.0, P < 0.001), landscapes (F6, 616 = 19.7, P < 0.001) and along distance from water (F18, 1742 = 8.8, P < 0.001, Fig. 4.4). The mean percentage cover of bare ground was similar between the dry and wet seasons but varied between landscapes and with increasing distance from water (P < 0.001, Fig. 4.4A), such that it was lower in the pastoral ranches than in the MMNR within 750 m from rivers but became higher in the pastoral ranches than the MMNR at greater distances from rivers. The mean percentage cover of grasses shorter than 10 cm was higher in the dry (0.81±0.02, n = 312) than the wet (0.59±0.02, n = 322, P < 0.001) season and in the pastoral ranches (0.92±0.03, n = 228) than the MMNR (0.57±0.02, n = 406, P < 0.001). It declined significantly with increasing distance from rivers (P < 0.001), but the decline was only significant for the MMNR (Fig. 4.4B). The mean percentage cover of grasses 10–30 cm tall was similar in both seasons and landscapes and increased significantly with distance from water similarly in both landscapes (P < 0.001, Fig. 4.4C). The mean percentage cover of grasses taller than 30 cm was higher in the wet (0.59±0.03, n = 322) than the dry (0.32±0.02, n = 312, P < 0.001) season, as well as in the MMNR (0.58±0.03, n = 406) than in the pastoral ranches (0.24±0.03, n = 228, P < 0.001). It also increased with increasing distance from rivers (P < 0.001), but the increase was only significant for the MMNR (Fig. 4.4D). The mean percentage cover of forbs was higher in the wet (0.14±0.01, n = 322) than the dry (0.11±0.01, n = 312, P = 0.05) season but similar in both landscapes and declined with increasing distance from Contrasting effects of hippo and livestock grazing 55 water similarly in both landscapes (P < 0.001, Fig. 4.4E). The mean percentage cover of shrubs was comparable between the dry and wet seasons but was higher in the pastoral ranches (0.07±0.01, n = 228) than in the MMNR (0.04±0, n = 406, P = 0.012). Furthermore, it declined significantly with distance from water, similarly in both landscapes (P < 0.001, Fig. 4.4F). A multivariate test of significance showed that grazing intensity was significantly related to percent cover of bare ground and vegetation categories (Wilks’ Lambda = 0.19, F18, 1768 = 76.8, P < 0.35 bare ground 0.30 0.25 acd 0.6 acd a 0.4 d a d a a a 0.2 0.05 0.00 mean cover (%) b cd 0.10 0.0 grass <10 cm B c 0.20 forbs E a abc abc 0.16 ab ab bd bc 0.8 ab bc 0.12 0.6 cd d 0.08 d 0.2 0.04 0.0 0.00 grass 10–30 cm C 0.5 pastoral ranches Masai Mara National Reserve 0.4 cd 0.2 bcd bcd d 0.08 abc bd 0.12 shrubs F a abc a 0.06 bc ab c 0.04 c c 0.02 0–0.75 1–2 2–3 distance from water (km) c 0.10 bcd 0.1 0.0 bcd d 0.4 0.3 b ac 0.15 1.0 b 0.8 a D 1.0 0.20 1.2 grass >30 cm A b 4–5 0.00 0–0.75 1–2 2–3 c 4–5 distance from water (km) Figure 4.4 Mean percent cover of vegetation and bare soil and interactions between landscape and distance from water in the Mara region of Kenya during 2007–2008. Grey and white bars denote the pastoral ranches and the Masai Mara National Reserve, respectively. Bars with similar letters in each category denote means that did not differ significantly. 56 Chapter 4 0.001), such that the cover of bare ground (P < 0.001), grasses shorter than 10 cm (P < 0.001), forbs (P < 0.001) and shrubs (P < 0.001) increased significantly with increasing grazing intensity, whereas the cover of grasses between 10-30 cm (P < 0.001) and taller than 30 cm (P < 0.001) declined with increasing grazing intensity. Species richness and floristic composition We recorded 145 plant species belonging to 98 genera and 40 families and comprising 31% forbs, 28% grasses, 23% trees and 18% shrubs. Plant species richness varied between landscapes, seasons and along distance from water (F13, 620 = 9.35, P < 0.001, Table 4.1). The mean number of plant species per 100 m2 plot was higher in the wet (15.44±0.25, n = 322) than the dry (11.89±0.26, n = 312) season. There was no significant difference in plant species richness between the MMNR (13.86±0.21, n = 406) and the pastoral ranches (13.74±0.32, n = 228; Table 4.1; Fig. 4.5). However, the number of plant species declined with distance from water in both landscapes (P = 0.012, Fig. 4.5) and was significantly influenced by grazing intensity (P < 0.001). In particular, species diversity was lower in patches of dense vegetation cover or bare ground than in patch mosaics supporting mixed short, medium and tall vegetation. Growth form characterization The mean number of forb, grass, shrub and tree species differed between landscapes (F4, 617 = 9.04, P < 0.001), seasons (F4, 617 = 29.66, P < 0.001) and along distance from water (F12, 1632 = 4.06, P < 0.001). Grazing intensity significantly modified the number of forb species (P < 0.001) but only marginally influenced the grass species (P = 0.085, Table 4.2). More forb species were recorded in the wet Table 4.1 Results of statistical tests of the effects of season, landscape, distance from water and their interactions on plant species richness in the Mara Region of Kenya. NDF is the numerator and DDF the denominator degrees of freedom. Effects NDF DDF Intercept 1 620 Landscape 1 620 Season 1 620 F P 10697.12 631.17 <0.001 62.46 3.69 0.055 1294.13 76.36 <0.001 MS Distance 3 620 62.69 3.70 0.012 Landscape × Season 1 620 15.17 0.89 0.345 Landscape × Distance 3 620 18.94 1.12 0.341 Season × Distance 3 620 12.80 0.76 0.520 Grazing intensity 1 620 183.38 10.82 0.001 Contrasting effects of hippo and livestock grazing 57 mean species richness (n/10 m2) 16 15 Figure 4.5 Mean number of plant species per 10 m2 as a function of distance from water in the Mara region of Kenya during 2007–2008. Solid and dashed lines denote the Masai Mara National Reserve and pastoral ranches, respectively. 14 13 12 Masai Mara National Reserve pastoral ranches 11 0 0.1 0.25 0.5 0.75 1 1.25 1.5 2 2.5 3 4 5 distance from water (km) (4.54±0.13, n = 322) than the dry (3.61±0.09, n=312, P < 0.001) season, in the MMNR (4.26±0.10, n = 406) than the pastoral ranches (3.78±0.13, n = 228, P < 0.001) and the number of forb species declined with distance from water, similarly in both landscapes (P = 0.010, Table 4.2). The number of grass species was higher in the wet (9.37±0.15, n = 322) than the dry (7.08±0.10, n = 312, P < 0.001) season, marginally higher in the MMNR (8.40±0.14, n = 406) than the pastoral ranches (7.98±0.16, n = 228, P = 0.046, Table 4.2) and did not change with distance from water in either landscape. The number of shrub species was similar in both seasons, higher in the pastoral ranches (1.68±0.12, n =228) than the MMNR (1.00±0.05, n = 406, P = 0.001) and declined significantly with distance from water in both landscapes (P < 0.001, Table 4.2). The decline was more marked in the pastoral ranches (P = 0.008). The mean number of tree species was similar between landscapes but declined significantly with increasing distance from water (P = 0.018) and the rate of decline was steeper for the pastoral ranches (P = 0.025, Table 4.2). Species similarity index and grazing impact signatures The reserve and the pastoral ranches had an overall plant species similarity index of 0.57. This index declined consistently with distance from water such that it was 0.50, 0.49, 0.41 and 0.29 at 0–0.75, 1–2, 2–3 and 4–5 km from water, respectively. The first two ordination (PCA) axes explained 31% of the variation in plant species composition between the two landscapes. Grazing intensity was the most important factor influencing species composition along the first axis independent of the number of hippo trails, while distance from water and number of hippo trails influenced species composition along the second axis (Fig. 4.6). The PCA ordination space clearly separated the reserve and pastoral ranches based on plant species composition, with four species clusters apparent: (a) species associated with high number of hippo trails and close to water, were exemplified by Aristida adoensis, Loudetia 58 Chapter 4 simplex, Sida ovate and Tragus berteronianus ; (b) species associated with distance from water in areas of low number of hippo trails clustered together and included Eragrostis racemosa, Acacia drepanolobium, and Athroisma psylloides; (c) species responding to heavy grazing irrespective of number of hippo trails and distance from water were represented by Cynodon dactylon, Microchloa kunthii, Sida massaica and Solanum incanum; and (d) species common in low or moderately grazed areas irrespective of distance from water were exemplified by Chloris gayana, Cymbopogon spp and Setaria incrassate (Fig. 4.6). Table 4.2 Results of statistical tests of the effects of landscape and distance from water and their interactions on the mean number of forb, grass, shrub and tree species in the Mara region of Kenya. NDF is the numerator and DDF the denominator degrees of freedom. Growth form Effects Forbs Shrubs Grasses Trees NDF DDF F P>F Intercept 1 633 165.99 <0.001 Landscape 1 633 18.11 <0.001 Season 1 633 37.85 <0.001 Distance 3 633 3.81 0.010 Landscape × Distance 3 633 0.69 0.582 Grazing level 1 633 15.40 <0.001 Intercept 1 633 46.54 <0.001 Landscape 1 633 12.44 Season 1 633 0.005 Distance 3 633 9.53 0.001 0.936 <0.001 Landscape × Distance 3 633 3.93 0.008 Grazing level 1 633 0.48 0.492 Intercept 1 633 738.66 <0.001 Landscape 1 633 4.08 0.046 Season 1 633 101.54 <0.001 Distance 3 633 1.01 0.386 Landscape × Distance 3 633 0.50 0.684 Grazing level 1 633 2.97 0.085 Intercept 1 633 5.26 0.016 Landscape 1 633 0.32 0.495 Season 1 633 1.64 0.108 Distance 3 633 3.28 0.018 Landscape × Distance 3 633 3.18 0.025 Grazing level 1 633 2.79 0.121 Contrasting effects of hippo and livestock grazing 59 R_0.5 R_0.25 Hippo trails Axis 2 R_0.1 MMNR Pastoral ranches TraguBER SidaOVA LoudeSIM R_1.25 Landscape legend AristADO R_0.75 SidaMAS R_1 R_1.5 MicroKUN CymbopSP SolanINC P_0.5 P_0.1 Axis 1 R_2 P_0.75 ChlorGAY SetarINC P_1 Grazing intensity P_1.25 CynodDAC P_0.25 P_3 P_1.5 P_2.5 R_2.5 R_3 R_4 Distance P_5 P_4 P_2 AcaciDRE R_5 AthroPSY Eragr.RAC Figure 4.6 Ordination diagram (PCA) based on plant species frequency, showing the influence of distance from water, grazing intensity and number of hippo trails on plant species composition in the Mara region of Kenya. Abbreviation refer to sampling locations and species abbreviation [R and P refer to reserve and pastoral ranches respectively and the preceding number is the location (km) from water, while species are abbreviated with the first 5-letter and first 3-letters in caps for Latin names]. Discussion The high grazing intensity recorded close to water in both landscapes is characteristic of gradients created by herbivores in areas of concentrated resource utilization (Thornton 1971; Lock 1972; Eltringham 1999; Fleischner 1994; Thrash 1998; Thrash 2000; Oba et al. 2001), such as areas close to water, especially in the dry season when water is limiting. However, grazing intensity declined steeply away 60 Chapter 4 from water in the reserve but not in the pastoral ranches, indicating more homogeneous distribution of grazing impact in the pastoral than the protected landscape. The heavily grazed strip right next to water had the highest number of hippopotamus trails in the reserve due to concentrated utilization by hippopotamus leaving and returning to water daily. In contrast, the more widespread impact of heavy grazing in the pastoral ranches was due to year-round grazing by resident livestock, occurring at high densities in the pastoral ranches. The difference in grazing intensity between the reserve and the pastoral ranches suggest that the impact of grazing by wild herbivores is more diffusely distributed over the landscape and fades faster away from water sources, resulting in the lower grazing intensity farther from water recorded for the reserve. However, the intense grazing impacts within the 750 m radius from rivers in the reserve implicate repeated grazing and trampling by hippopotamus (Thornton 1971; Lock 1972; Eltringham 1999). Higher concentrations of livestock reduced vegetation cover and plant height over longer distances from water in the pastoral ranches than the reserve. Repeated grazing and trampling by hippopotami leaving and returning to water daily in the reserve created sacrificial zones devoid of most vegetation cover and extending for nearly 750 m from river banks, similar to findings of earlier studies (Lock 1972; Eltringam 1999; Thrash and Derry 1999). These sacrificial zones were characteristically denuded and had the highest grazing intensity scores and percent cover of short grasses and forbs. In contrast, the higher percent cover of bare ground beyond 750 m from water in the pastoral ranches than the reserve can be largely attributed to heavy and sustained grazing and trampling by large herds of livestock. Grass height was markedly shorter closer to water in both landscapes and declined significantly with increasing distance from water in the reserve but not in the pastoral ranches, where short grasses dominated up to 5 km from water. Forbs were well represented 2-3 km from water in both landscapes but their contribution to ground cover decreased sharply thereafter, implying that forbs favored short grass lawns created and maintained by heavy grazing close to water. Shrub cover was higher closer to water in both landscapes and farther from water in the ranches than in the reserve, implying that heavy grazing enhanced thickening and spread of shrubs, through suppression of fires and reduced competition with grasses (Moleele and Perkins 1998; Thrash 1998; Oba et al. 2000; Sharp and Whittaker 2003; Lunt et al. 2007). Grazing patterns and impacts varied spatially, creating discernible spatial heterogeneity in vegetation structure and species composition (McNaughton 1983; Olff and Richie 1998), especially in the reserve. Notably, areas closer to water were typically more heavily grazed than distant areas in the reserve, similar to other observations of utilization gradients emanating from points of countertraded use known as piospheres (Andrew 1988; James et al. 1999). The differences in the patterns of spatial heterogeneity in vegetation structure away from rivers between Contrasting effects of hippo and livestock grazing 61 the two landscapes could reflect differences in hippopotamus and livestock grazing styles and their resultant impacts on vegetation. Although high grazing intensity maintained grass cover at relatively low levels, grasses nevertheless constituted the major fraction of the herbaceous layer. Also, the observed seasonal variation in vegetation cover, suggest that forage availability is limiting in the dry season as indicated by intensification of impacts of grazing close to water. Despite their differences in grazing intensity and vegetation structure, both landscapes had similar plant species richness. Species richness was highest at intermediate grazing intensity scores in the reserve, consistent with predictions of the intermediate disturbance hypothesis for mesic savannah rangelands (Grime 1973), suggesting that moderate grazing pressure enabled coexistence of many plant species thereby enhancing herbaceous species richness (Whicker and Detling 1988; Olff and Richie 1998; Oba et al. 2001). However, at high and low grazing intensity scores, species richness declined in the reserve due to domination by a few species, as has also been observed elsewhere (Del-Val and Crawley 2005; Lunt et al. 2007). This was not the case for the pastoral ranches where the intermediate level of grazing intensity was not evident but species richness still followed a humped distribution from water. This contrast further reflects the contrasting grazing strategies of hippopotamus and livestock, the two dominant constituents of the grazing large mammal community in the riparian-edge habitats of Masai Mara. In the reserve, the impact of hippopotamus grazing created discrete shifting mosaics of tall, medium and short vegetation cover that promoted the coexistence of herbaceous species, especially at moderately grazed locations from water. In the pastoral ranches, by contrast, livestock grazing was heavy, creating wide patches of bare ground and homogenized the structural vegetation pattern, thus enhancing the establishment of annual and invasive species, which also elevated species richness at intermediate distances from water similar to patterns found elsewhere (Zerihun and Saleem 2000). Therefore, grazing of the riparian zone by hippopotamus and livestock in the Mara had contrasting impacts but allowed diverse herbaceous species to coexist. The numerical predominance of forbs within heavily grazed patches is consistent with findings of several other studies (Whicker and Detling 1988; Del-Val and Crawley 2005), while the high number of plant species recorded in the wet season probably reflects germination of annual species (Zerihun and Saleem 2000). The number of forb species reduced with increasing distance from water implying that grasses outcompeted forbs in areas of low grazing intensity (Oba et al. 2001; Del-Val and Crawley 2005). Surprisingly, the number of grass species did not change along the distance-to-water gradient in both landscapes, suggesting that it was insensitive to average vegetation height, and was only marginally responsive to grazing intensity. Woody species (shrubs and trees) were consistently more abundant closer to water and in the pastoral ranches, implying that intense grazing close to water 62 Chapter 4 by hippopotamus in the reserve and livestock in the ranches kept grasses short all year, thereby suppressing fires and stimulating encroachment of woody species (Moleele and Perkins 1998; Oba et al. 2000; Sharp and Whittaker 2003; Lunt et al. 2007). Our results thus demonstrate that both high and low intensities of grazing can reduce plant species richness, most notably by altering the species composition of forbs and shrubs. Although plant species richness was similar between the reserve and the pastoral ranches, differences in species composition sufficiently separated the two landscapes in the PCA ordination space. Additionally, the Jaccard’s similarity index showed that both landscapes shared 57% of the species recorded; the similarity index also declined considerably away from water in response to differences in grazing gradients between the landscapes. Variations in species composition in the reserve are explained by distance from water, number of hippo trails and grazing intensity. In contrast, variations in species composition in the pastoral ranches are less explained by distance from water but mostly by grazing intensity. Notably, areas far away from water (4–5 km) in the pastoral ranches have similar species composition to areas close to water (0.1–0.5 km) in the reserve, while species compositions within 1–5 km in reserve and 0.1–3 km in the pastoral ranches are distinctive to each landscape (Fig. 4.6). The differences in species composition between the reserve and pastoral ranches are clearly discernable; and are probably because of the added effects of heavy year-round livestock grazing in the pastoral ranches. Large herds of migratory herbivores only use the reserve half-year, allowing sufficient time for vegetation recovery. Therefore, we attribute differences in species composition to the different modes and intensities of hippopotamus and livestock grazing on vegetation structure and spatial heterogeneity between the reserve and ranches (Thrash 2000). Certainly, different factors are driving plant species composition between the reserve and ranches resulting to species clusters in the landscapes. Heavily grazed areas especially in the pastoral ranches retained species like Cynodon dactylon which is a grazing lawn species, Microchloa kunthii which establishes well in degraded areas, an increaser species like Sida massaica and invasive species like Solanum incanum (Fig. 4.6). Areas highly utilized by the hippos and mostly in the reserve had typical species such as Aristida adoensis which is common in highly grazed areas; an increaser species like Sida ovate, weeds such as Tragus berteronianus, and a low palatable grass Loudetia simplex. Species associated with distance from water and in areas less utilized by hippos but commonly in the pastoral ranches included Eragrostis racemosa, Athroisma psylloides and Acacia drepanolobium. However, areas in the reserves that were moderately grazed irrespective of distance from water had a typical species cluster that included Setaria incrassate which only survives in moderately grazed areas; Cymbopogon spp and Chloris gayana, a high quality pasture grass. Therefore, the data demonstrate that differen- Contrasting effects of hippo and livestock grazing 63 tial modes and intensities of grazing by hippopotamus and livestock along riparianedge habitats of Masai Mara have significantly and differentially modified plant species composition. Furthermore, changes in vegetation structure, plant species richness and composition induced by hippopotamus and livestock created habitat and forage diversity that may influence the suitability of riparian habitats for other mammalian herbivore species in the Mara. Conclusion We assumed that the effects of soils and other herbivores on vegetation structure and grazing intensity would be comparable between the reserve and pastoral ranches because both landscapes are broadly similar, are adjacent to each other and are not separated by physical barriers to animal movements. Therefore, patterns in grazing intensity and vegetation structure detected along the riparian zones in the reserve and the pastoral ranches could be, either directly or indirectly related to impacts of hippopotamus and livestock grazing. The gradients in impacts of grazing we observed altered vegetation structure, species richness and composition. Despite more intense grazing and associated reduction in vegetation cover in the pastoral ranches, species richness was similar between the reserve and the ranches, suggesting that vegetation structure and species composition responded differentially to grazing impacts. Species richness indices concealed important shifts in plant species composition that occurred along the distance-to-water gradient in response to varying impacts of grazing. The increasing sedenterization of the Masai pastoralists and their livestock in the pastoral ranches of the Mara, will progressively increase both the intensity and extent of the impact of livestock grazing, thereby shifting the vegetation composition towards annuals and invasive weedy species and further suppressing fires and promoting the establishment and spread of woody species encroachment, and lowering the quality of the pastoral rangelands for wildlife. The long-term consequences of these impacts are still unclear and hard to predict but continued densification of woody species may reduce the suitability of the pastoral landscapes for livestock and other grazing wild herbivores. Acknowledgements We thank Charles Matankory and Sospeter Kiambi for assistance with field work and for arranging field logistics. We also thank the Kenya Wildlife Service rangers for providing security during field work, wardens of the Masai Mara National Reserve and the management of the Koyiaki, Lemek and Ol Chorro Oiroua pastoral ranches for allowing us unlimited access to the study area. EK was supported by the Netherlands Fellowship Program (NFP) and the University of Groningen through the Government of Kenya and by the Frankfurt Zoological Society (FZS). 64 Chapter 4 Contrasting effects of hippo and livestock grazing 65 Chapter five 5 Hippopotamus and livestock grazing: influences on riparian vegetation and facilitation of other herbivores in the Mara Region of Kenya Erustus M. Kanga, Joseph O. Ogutu, Hans-Peter Piepho and Han Olff Published in Landscape and Ecological Engineering (2011), DOI: 10.1007/s11355-011-0175-y Abstract Riparian savanna habitats grazed by hippopotamus or livestock experience seasonal ecological stresses through depletion of herbaceous vegetation, and are often points of contacts and conflicts between herbivores, humans and their livestock. We investigated how hippopotamus and livestock grazing influence vegetation structure and cover and facilitate other wild herbivores in the Mara Region of Kenya. We used 5 km-long transects, each having 13 plots measuring 10 × 10 m2 and radiating from rivers in the Masai Mara National Reserve and adjoining community pastoral ranches. For each plot, we measured the height and visually estimated the percent cover of grasses, forbs, shrubs and bare ground, herbivore abundance and species richness. Our results showed that grass height was shortest closest to rivers in both landscapes, increased with increasing distance from rivers in the reserve but was uniformly short in the pastoral ranches. Shifting mosaics of short grass lawns interspersed with patches of medium to tall grasses occurred within 2.5 km from rivers in the reserve in areas grazed habitually by hippos. Hence, hippo grazing enhanced structural heterogeneity of vegetation but livestock grazing had a homogenizing effect in the pastoral ranches. The distribution of biomass and species richness of other ungulates along distance from rivers followed the quadratic pattern in the reserve, suggesting that hippopotamus grazing attracted more herbivores to the vegetation patches at intermediate distances from rivers in the reserve. However, the distribution of biomass and species richness of other ungulates followed a linear pattern in the pastoral ranches, implying that herbivores avoided areas grazed heavily by livestock in the pastoral ranches, especially near rivers. 68 Chapter 5 Introduction African savannas support a diverse indigenous herbivore assemblage besides livestock production by pastoral communities (Skarpe 1991). Understanding the spatial and temporal dynamics of savannas used by wild herbivores, livestock and people is essential for their effective management for wildlife conservation and for promoting human well-being (Coughenour 1991; Baily et al. 1996). The distribution of herbivores within landscapes is influenced by the composite effects of biotic factors such as competition, species composition, forage quality and quantity, and abiotic factors such as topography and distance to water (Milchunas and Laurenroth 1993; Bailey et al. 1996; Illius and O’Connor 2000; Adler et al. 2001; Landsberg et al. 2003; Redfern et al. 2003). In particular, the distribution of herbivores in arid and semi-arid savannas is strongly influenced by the location of surface water and nutritious forage, especially during the dry season, when water becomes progressively limiting and water sources become points of contact and conflict between herbivores, humans and their livestock (Western 1975; Fryxell and Sinclair 1988; Illius and O’Connor 2000). Forage production in savannahs is primarily limited by rainfall, which varies considerably in space and time, producing patchiness in green forage and ephemeral water availability (Deshmukh 1984; Boutton 1988). However, African herbivores have adapted to the seasonal variability in forage and water by regular seasonal migrations or irregular and unpredictable dispersal movements between water and forage resources (Fryxell and Sinclair 1988; Fryxell et al. 1988). Furthermore, herbivore distribution patterns in response to resource variability reflect trade-offs between satisfying their water and forage requirements and minimizing predation risk (Bergman et al. 2001; Bailey et al. 1996). Herbivore functional groupings based on body size, dietary guild, foraging behavior and digestive physiology, may further explain variations in patterns of their distributions (Jarman 1974; Demment et al. 1985; Wilmshurst et al. 2000). Thus, among the more waterdependent herbivores, large-sized animals should travel further distances from water sources than small animals to satisfy their forage quantity requirements. The less water dependent herbivores such as browsers are less constrained by distance to water sources (Western 1975; Redfern et al. 2003). Nevertheless, during dry seasons, more rapid depletion of forage occurs near water sources. At the landscape scale, radial gradients in vegetation characteristics originating from areas of concentrated resource use provide evidence for how herbivores influence vegetation patterns. Herbivore grazing impacts in savannas are higher closer to water points, creating utilization gradients termed piospheres (Lange 1969; Andrew 1988; Thrash 1998, 2000; Thrash and Derry 1999). However relatively little is known about the development of piosphere gradients in ecosystems supporting diverse assemblages of large wild herbivores, livestock and pastoralists, Hippo and livestock grazing, facilitation of other herbivores 69 such as the semi-arid savanna ecosystems of East Africa. Riparian savanna habitats in such ecosystems, if also grazed heavily by hippopotamus (Hippopotamus amphibious Linnaeus 1758) or livestock, may experience seasonal ecological stresses through depletion of herbaceous vegetation and increased denudation (Thornton 1971; Lock 1972; Fleischner 1994; Eltrigham 1999; Oba et al. 2000). While most wild herbivores are highly mobile and distribute their grazing impacts more evenly over the landscape, hippos and pastoral livestock are typically centralplace foragers because hippos must leave and return to water whereas pastoral livestock must leave and return to pastoral settlements daily. This creates zones of attenuating impacts from water and settlements (Ogutu et al. 2010), which, in turn, affect the use of riparian habitats and pastoral landscapes by other herbivores. Hippo grazing can be potentially destructive to vegetation due to a combination of their large daily food requirements and characteristic grazing style of plucking grass (Lock 1972; Eltrigham 1974; Thornton 1971). Similarly, heavy livestock grazing can be detrimental to wildlife habitats (Jones 1981; Quinn and Walgenbach 1990; Fleischner 1994), except under well-managed grazing conditions (Vavra 2005). Fleischner (1994) underscored this point by asserting that the ecological costs of livestock grazing include the general loss of biodiversity, manifested in reduced population densities of a wide variety of taxa, as well as aiding the spread of alien and weedy species; disrupting ecosystem functions, including nutrient cycling and succession; changes in community organization and vegetation stratification and damage to soils. Hippos not only pluck grass but also create and maintain short grass lawns in areas where they preferentially feed (Olivier and Laurie 1974; Eltringham 1999; Arsenault and Owen-Smith 2002). The mosaics of closely cropped grass lawns interspersed with areas of long grass alter vertical vegetation structure and create patchy landscapes of varying vegetation height and cover. This increases spatial heterogeneity in vegetation structure (Hobbs 1996; Adler et al. 2001), which is important to other wildlife through its indirect effects on competition, facilitation and predator-prey relationships (Prins and Olff 1998; Murray and Illius 2000). The enhanced structural diversity of vegetation patches can facilitate other herbivores, that differentially select vegetation patches with intermediate biomass and highquality forage (Wilmshurst et al. 2000; Prins and Olff 1998; Olff et al. 2002; Arsenault and Owen-Smith 2002), and avoid patches with higher predation risk, such as tall grasslands, and other potential predator ambush sites (Hernandez and Laundre 2005; Verdolin 2006). In contrast, relatively few systematic investigations have found positive benefits of livestock grazing to other wild herbivores (Belsky et al. 1999). As such, the effects of livestock grazing on wildlife populations is an important conservation concern (Fleischner 1994; Prins 2000). In recent decades, human-induced land use changes, excessive resource extraction, and erection of artificial barriers have increasingly threatened savanna 70 Chapter 5 ecosystems through reduction of grazing areas and disruption of access to water sources. Consequently, declining savanna rangelands and sedentarization of pastoralists (Kimani and Prichard 1998; Homewood et al. 2001; Lamprey and Reid 2004; Western et al. 2009) and the associated expansion of settlements and cultivation and intensification of livestock grazing could fundamentally modify the spatial distribution and movement patterns of herbivores and heighten competition between livestock and wildlife (Prins and Olff 1998). This could accelerate degradation and fragmentation of rangelands and cause declines in wild herbivore populations (Verlinden 1997; Serneels et al. 2001). If such savannah habitats are utilized by both hippos and livestock, they may be expected to compete for limiting grazing resources, especially close to water points. Furthermore, because hippo and livestock grazing can differentially modify vegetation structure, they may have contrasting effects on the species richness, abundance and distribution of other wildlife species, especially in dry seasons when most large herbivores concentrate within 5 km radius of water in semi-arid savannas (Western 1975; Redfern et al. 2003). Our limited current understanding of these processes support the need for investigations that encompass both protected and pastoral systems and elucidate how hippo and livestock grazing modify the structure of riparian-edge habitats and their utilization by other wild ungulates in savannas. We investigated the effects of hippopotamus and livestock grazing along a riparian habitat in the Masai Mara region of Kenya, to address the following two overarching questions: (1) How does hippo and livestock grazing modify vegetation structure and cover along distance from rivers in semi-arid savannas? (2) How does the impact of hippo and livestock grazing on vegetation along distance from water influence the distribution of biomass and species richness of the other wild ungulates? We expected hippo and livestock grazing activities to have contrasting effects on vegetation structure and cover based on differences in their grazing strategies: hippos pluck grasses, create and maintain short grass lawns while livestock are bulk grazers, and frequently uproot shallow-rooted grasses. We also hypothesized that if the intensity of grazing declines with increasing distance from water sources, then vegetation height and basal cover will increase with distance from water in both hippo and livestock dominated landscapes. Since hippos create and maintain mosaics of short grass lawns intermixed with medium to tall grasses and livestock grazing creates uniformly short grasslands, hippo-dominated areas will be more spatially heterogeneous and attract a more diverse array and abundance of other wild herbivore species close to water but wild herbivores will tend to avoid areas near water in livestock-dominated areas. Tests of these hypotheses are essential to predicting the long-term effects of sedentarization of pastoralists and the associated intensification of land use and competition between livestock and herbivores around water sources due to declining forage resources. Hippo and livestock grazing, facilitation of other herbivores 71 Methods Study area The Mara Region (Mara) is located in south western Kenya, between latitudes 34º45´ E and 36º00´ E and is bounded by the Serengeti National Park (SNP) in Tanzania to the south and Siria escarpment to the west (Fig. 5.1). This region forms the northernmost limit of the Serengeti-Mara ecosystem, covering some 25,000 km2 and straddling the Kenya-Tanzania boundary. The ecosystem comprises several wildlife conservation administrations and conservation-pastoralist multiple land use zones in each of the two countries (Sinclair and Arcese 1995). The Mara covers about 5,500 km2, with the Masai Mara National Reserve (MMNR) covering some 1,530 km2 while the adjacent pastoral ranches, including Koyiaki (931 km2), Olkinyei (787 km2), Siana (1316 km2), Lemek (717 km2) and Ol Chorro Oiroua (59 km2) cover a combined total of about 4,000 km2. The Mara receives an annual rainfall of about 600 mm in the south east, rising to about 1300 mm at the north western edge (Norton-Griffiths et al. 1975; Ogutu et al. in press). Rainfall is bimodal, with the short rains falling from November to December and the long rains from January to June, though January and February are often dry. The vegetation is predominantly grassland, with isolated scrublands and woodlands, especially along the drainage lines and on hill tops (Epp and Agatsiva 1980). Several rivers and numerous streams drain the Mara, with the Mara River being the only permanent river. Sand, Talek and Olare-Orok Rivers, the main tributaries of the Mara River, are largely seasonal. The Mara River is about 396 km long and its flow through the MMNR and SNP sustains a large variety of abundant herbivore species, 10 of which form the main focus of this study and include the hippopotamus (Hippopotamus amphibious, Linnaeus 1758), wildebeest (Connochaetes taurinus, Burchell 1823), Burchell's zebra (Equus burchelli, Gray 1824), the African buffalo (Syncerus caffer, Sparrman 1779), topi (Damaliscus korrigum, Ogilby 1837 ), Coke’s hartebeest (Alcelaphus buselaphus, Gunther 1884), Grant’s gazelle (Gazella granti, Brooke 1872), Thomson’s gazelle (Gazella thomsoni, Günther 1884), warthog (Phacochoerus aethiopicus, Gmelin 1788) and impala (Aepyceros melampus, Lichtenstein 1812). Populations of these herbivore species face water-related constraints in the Mara in the dry season, including increasing water shortages and declining water quality linked to expanding irrigated cultivation, unregulated water extractions and deforestation of the Mau Forest catchments of the Mara River (Mati et al. 2008). Marked declines in herbivore numbers in the Mara have been attributed to their progressive exclusion from the pastoral ranches by land use changes, including expanding mechanized and subsistence agriculture and settlements, which have affected over 8% of the Mara and caused land cover changes in at least 36% of the pastoral ranches adjoining the MMNR (Homewood et al. 2001; Lamprey and Reid 72 Chapter 5 a rou rr Kenya O ho lC i oO N Lemek 20 Nairobi 19 Tanzania 18 Olkinyei 15 24 23 14 21 17 9 25 13 7 11 Koyiaki 22 12 4 10 Se 5 km transects ren get iN atio 5 6 3 1 2 nal Pa rk, MMNR Tan z ani a 16 Siana Kenya 20 km Figure 5.1 Map of Masai Mara National Reserve and the adjoining pastoral ranches showing the transects (numbered), radiating from rivers, sampled during 2007–2008. The four study sites were the protected Masai Mara National Reserve (1530 km2) and the Koyiaki (931 km2), Lemek (717 km2) and Ol Chorro Oiroua (59 km2) pastoral ranches. 2004; Mati et al. 2008). These changes have intensified competition between livestock and wild herbivores in the pastoral ranches of the Mara. Moreover, sedentarization of the formerly semi-nomadic Maasai pastoralists (Kimani and Pickard 1998, Western et al. 2009) and the associated intensification of land use and grazing by large numbers of livestock in the pastoral ranches accelerate range degradation and fragmentation, including along riparian habitats. Rising temperatures and recurrent droughts (Ogutu et al. 2007) have further amplified herbivore mortalities in the Serengeti-Mara ecosystem. Sampling design We selected two landscapes; a protected conservation reserve, the Masai Mara National Reserve, and the adjoining community pastoral ranches of Koyiaki, Lemek and Ol Chorro Oiroua (Fig. 5.1). Livestock grazing is prohibited in the reserve except Hippo and livestock grazing, facilitation of other herbivores 73 for illegal incursions but livestock and wildlife graze together in the pastoral ranches. We established 25 random transects, each 5 km long and radiating from the Mara, Talek and Olare Orok Rivers. Sixteen transects were located in areas grazed by hippopotamus and other wild herbivores, while another nine transects were placed in areas grazed by livestock, hippos and other wild herbivores (Fig. 5.1). However, along the 5 km riparian strip, hippos and livestock are the main resident grazers in the MMNR and the pastoral ranches, respectively. Topography increased rather gently away from rivers within the 5 km distance sampled by transects in both the reserve (range 1668 m to 1718 m) and the pastoral ranches (1773 m to 1836 m). Along each transect, we established 13 sampling plots each measuring 10 × 10 m2 at distances of 0, 100, 250, 500, 750, 1000, 1250, 1500, 2000, 2500, 3000, 4000 and 5000 meters from rivers. In each plot, we visually estimated the percent cover of three growth forms of vegetation (grasses, forbs and shrubs) and bare ground. Grasses were further subdivided into three height classes: less than 10 cm tall, 1030 cm, and greater than 30 cm. The cover measurements provided a simple, quick and efficient method for assessing rangeland conditions. To estimate how herbivores other than hippo and livestock utilized the landscape, we counted all herbivore dung or pellet piles in each plot. Dung and pellet counts are likely reliable as relative measures of habitat use by herbivores because none of the herbivore species we studied is strictly territorial. Additionally, we enumerated all herbivores sighted within 200 m on either side of each plot. To indicate how herbivores utilize the rangelands in space and time, the herbivore counts were converted to biomass using unit weights in Coe et al. (1976). Further, we assessed herbivore predation risk by estimating the percentage visibility of a predator concealed in vegetation at a distance of 30 m from the centre of each plot along 0°, 90°, 180° and 270° bearings using the method of Hopcraft (2002). Finally, because hippos have been shown to create and maintain mosaics of short-grass lawns, we counted all hippopotamus trails within a 50 m radius from the center of each plot. Field samplings were carried out during the early dry (July-August) and late dry (September-October) seasons of 2007 and 2008 and in the late wet season (March-April) of 2008. We were unable to access the study area to obtain samples for the early wet (JanuaryFebruary) season of 2008 as scheduled due to the outbreak of widespread post-election violence in Kenya at the time. Transects were treated as the unit of replication. The total of 650 samples (n = 325 plots × 2 seasons) dropped to 636 as 14 samples (n = 8 for the reserve and n = 6 for the ranches) were discarded because the associated plots were either burned in the dry season, or were inaccessible in the wet season due to heavy rainfall. The 16 transects used in the reserve therefore produced 406 samples during the wet and dry seasons combined whereas the 9 transects used in the pastoral ranches produced 230 samples over the same period. 74 Chapter 5 Data analysis We used a multivariate generalized linear model to relate the proportions of vegetation cover in different growth forms and bare ground and the number of hippo trails to distance from water, landscape, season and their interactions, assuming a binomial error distribution and a logit link function (Ruppert et al. 2003). We used a multivariate test of significance to evaluate the significance of the relationships between the number of hippo trails and the proportions of grass cover and bare ground. Further, we used a generalized linear model with a log-normal error distribution and the identity link function to relate aggregate herbivore biomass, dung piles and species richness to distance from water, landscapes, seasons and their interactions. Finally, we used a multiple linear regression to relate vegetation structure to predation risk and herbivore biomass. Herbivore counts were converted to biomass, aggregated over all species and log-transformed whereas the percentage cover of vegetation was arcsine square-root transformed prior to analyses. We performed residual and influence diagnostics to evaluate the goodness-of-fit of the selected models and examined plots of distributions of residuals against the linear predictors, Q-Q plots of the normal distribution, box-whisker plots of residuals and frequency histograms of residuals to detect outliers or departure from normality. Preliminary analyses showed no significant differences in the distribution patterns away from rivers for the early dry (July-August) and late dry (September-October) season samples within either 2007 or 2008, or between both years. Therefore, we averaged (pooled) the early and late dry season samples of 2007 and 2008 to obtain one dry season sample for both years, which we compared with the late wet season (April-May) sample of 2008 in the analyses. All models were fitted in Statistica version-8 (StatSoft 2007) and in the SAS GLIMMIX procedure (SAS Institute 2009). Results Distribution of hippo trails from water The mean number of hippo trails was significantly higher (F1, 584 = 36.9, P < 0.001) in the MMNR (0.31±0.02, n = 406 samples) than in the pastoral ranches (0.13±0.02, n = 230). Hippo trails declined significantly with distance from rivers (F12, 584 = 10.8, P < 0.001) and this pattern was similar in both landscapes (F12, 584 = 1.5, P = 0.147; Fig. 5.2). During the wet season, hippos actively utilized a strip within 2.5 km on either side of the rivers in both landscapes but extended this to 3 km in the pastoral ranches and 4 km in the MMNR during the dry season. Distributions of vegetation cover from water The mean percentage cover of the five components of vegetation differed significantly across seasons (F6, 589 = 12.6, P < 0.001), landscapes (F6, 589 = 19.5, P < 0.001) Hippo and livestock grazing, facilitation of other herbivores 75 mean number of hippo trails 1.0 Masai Mara National Reserve pastoral ranches 0.8 Figure 5.2 Mean number of hippopotamus trails as a function of distance from water in the Mara Region of Kenya during 2007–2008. Solid and dashed lines denote the Masai Mara National Reserve and pastoral ranches, respectively. 0.6 0.4 0.2 0.0 0 0.1 0.25 0.5 0.75 1 1.25 1.5 2 2.5 3 4 5 distance from water (km) and along distance from water (F72, 3210 = 3.9, P < 0.001, Fig. 5.3, Table 5.1). The mean percentage cover of bare ground was similar in both seasons and landscapes, but declined significantly with increasing distance from water (P < 0.001), and the pattern of this decline varied between landscapes (P < 0.001), such that the percent cover of bare ground was lower in the pastoral ranches than in the MMNR within 500 m from rivers but became higher in the ranches than the reserve at greater distances from rivers (Fig. 5.3A). The mean percentage cover for grasses shorter than 10 cm was higher in the dry (0.85±0.03, n = 313) than the wet (0.64±0.03, n = 323, P < 0.001) season, in the pastoral ranches (0.92±0.03, n= 230) than in the MMNR (0.57±0.02, n = 406, P < 0.001) and declined significantly with increasing distance from rivers (P = 0.009). The declines with distance was significant for the MMNR but not for the pastoral ranches (Fig. 5.3B). The mean percentage cover of grasses 10–30 cm tall was similar in both seasons, but was marginally higher in the MMNR (0.28±0.02, n =406) than in the pastoral ranches (0.23±0.02, n = 230, P = 0.072). For the reserve, the percent cover of grasses in the 10–30 cm height class first increased up to 1.25 km from water and then declined with further increase in distance from rivers. For the ranches, the corresponding percent cover increased from the river up to 0.75 km, declined between 0.75 km and 2 km and increased thereafter (Fig. 5.3C). The mean percentage cover for grasses taller than 30 cm was higher in the wet (0.54±0.03, n = 323) than the dry (0.28±0.03, n = 313, P < 0.001) season, in the MMNR (0.58±0.03, n = 406) than in the pastoral ranches (0.25±0.03, n = 230, P < 0.001) and increased significantly away from rivers. The increase was steeper in the MMNR than the pastoral ranches after 0.5 km from water (P = 0.001, Fig. 5.3D). The mean percentage cover of forbs was higher in the wet (0.14±0.01, n = 323) than the dry (0.11±0.01, n = 313, P = 0.007) season, similar in both landscapes but first increased with increasing distance from water and then declined steadily thereafter in both landscapes (P < 0.001, Fig. 5.3E). For shrubs, the mean percentage 76 Chapter 5 cover was similar in the dry and wet seasons but higher in the pastoral ranches (0.06±0.01, n = 230) than the MMNR (0.04±0.00, n = 406, P = 0.009) but declined similarly with distance from water in both landscapes (P < 0.001, Table 5.1, Fig. 5.3F). A multivariate test of significance showed that there were significant relationships between hippo trails and percent cover of bare ground and grasses (Wilks’ Lambda = 0.81; F6, 627 = 12.4, P < 0.001), such that the cover of bare ground (P < 0.6 bare ground Masai Mara National Reserve pastoral ranches 0.5 mean cover A 0.4 D forbs E shrubs F 0.8 0.6 0.2 0.4 0.1 0.2 0.0 0.0 grass <10 cm B 1.0 mean cover grass >30 cm 1.0 0.3 1.2 0.20 0.16 0.8 0.12 0.6 0.08 0.4 0.04 0.2 0.0 0.5 mean cover 1.2 0.00 grass 10–30 cm C 1.0 0.4 0.8 0.3 0.6 0.2 0.4 0.1 0.02 0.0 0.00 0 0.1 0.25 0.5 0.75 1 1.25 1.5 2 2.5 3 distance from water (km) 4 5 0 0.1 0.25 0.5 0.75 1 1.25 1.5 2 2.5 3 4 5 distance from water (km) Figure 5.3 Mean percent cover of vegetation and bare soil and interactions between landscape and distance from water in the Mara Region of Kenya during 2007–2008. Solid and dashed lines denote the Masai Mara National Reserve and pastoral ranches, respectively. Hippo and livestock grazing, facilitation of other herbivores 77 Table 5.1 Results of statistical tests of the effects of season, landscape, distance from water and their interactions on the mean percentage cover of bare ground, grass and shrubs in the Mara Region of Kenya. NDF is the numerator and DDF the denominator degrees of freedom, respectively. Variable Effects NDF DDF F P>F FBare ground Intercept Season Landscape Distance Season × Landscape Season × Distance Landscape × Distance 1 1 1 12 1 12 12 594 594 594 594 594 594 594 805.5 1.6 2.0 11.9 0.9 0.4 5.3 <0.001 0.209 0.154 <0.001 0.345 0.968 <0.001 Grass <10 cm Intercept Season Landscape Distance Season × Landscape Season × Distance Landscape × Distance 1 1 1 12 1 12 12 594 594 594 594 594 594 594 1589.8 29.5 87.1 4.6 0.3 0.5 3.0 <0.001 <0.001 <0.001 <0.001 0.617 0.886 0.009 Grass 10–30 cm Intercept Season Landscape Distance Season × Landscape Season × Distance Landscape × Distance 1 1 1 12 1 12 12 594 594 594 594 594 594 594 295.9 1.1 3.2 2.4 0.1 0.8 1.2 <0.001 0.306 0.072 0.005 0.775 0.644 0.315 Grass >30 cm Intercept Season Landscape Distance Season × Landscape Season × Distance Landscape × Distance 1 1 1 12 1 12 12 594 594 594 594 594 594 594 378.4 37.5 60.9 3.6 0.1 0.6 2.7 <0.001 <0.001 <0.001 0.002 0.782 0.862 0.001 Forbs Intercept Season Landscape Distance Season × Landscape Season × Distance Landscape × Distance 1 1 1 12 1 12 12 594 594 594 594 594 594 594 583.6 7.4 0.5 5.0 0.1 0.5 0.3 <0.001 0.007 0.475 <0.001 0.755 0.897 0.988 Shrubs Intercept Season Landscape Distance Season × Landscape Season × Distance Landscape × Distance 1 1 1 12 1 12 12 594 594 594 594 594 594 594 195.3 0.2 7.0 5.4 0.0 0.3 1.0 <0.001 0.639 0.009 <0.001 0.884 0.992 0.469 78 Chapter 5 0.001), forbs (P < 0.001) and grasses shorter than 10 cm (P = 0.002) increased significantly with increasing number of hippopotamus trails, whereas the cover of grasses taller than 30 cm (P = 0.001) declined with increasing number of trails. Herbivore dung piles, biomass and species richness The mean number of dung piles per plot was significantly higher in the dry (1.28±0.12, n = 313) than the wet (0.39±0.11, n = 323, Table 5.2) season, reflecting the influx of the migratory herbivores in the dry season. There were more dung piles per plot in the MMNR (1.07±0.10, n = 406) than the pastoral ranches (0.60±0.13, n = 230) but this pattern varied seasonally such that in the dry season the MMNR had more dung piles per plot (1.69±0.22, n = 199) than the pastoral ranches (0.84±0.19, n = 114) whereas in the wet season the numbers of dung piles were similar between the MMNR (0.42±0.06, n = 207) and the pastoral ranches (0.37±0.08, n = 116). Table 5.2 Results of statistical tests of the effects of season, landscape, distance from water and their interactions on the density of herbivore dung piles in the Mara Region of Kenya. NDF is the numerator and DDF the denominator degrees of freedom, respectively. Effects IIntercept Season Landscape Distance Season × Landscape Season × Distance Landscape × Distance NDF DDF MS 1 1 1 12 1 12 12 596 596 596 596 596 596 596 71.84 10.54 2.93 0.33 1.53 0.31 0.13 F P 200.90 29.49 8.18 0.92 4.29 0.87 0.36 <0.001 <0.001 0.004 0.523 0.039 0.582 0.977 The total herbivore biomass was significantly higher in the dry (3.79±0.25, n = 313) than the wet (2.04±0.24, n = 323; Table 5.3) season. The MMNR had more herbivore biomass (3.46±0.21, n = 406) than the pastoral ranches (2.38±0.28, n = 230), and biomass increased significantly linearly with distance from water in the ranches (Fig. 5.4). In the MMNR, by contrast, the total herbivore biomass increased with distance from water up to 0.5 km, declined between 0.5 and 2 km from water and then increased thereafter (Fig. 5.4). Herbivore species richness was significantly higher during the dry (1.05±0.02, n = 313) than the wet (0.87±0.23, n = 323) season and was higher in the MMNR (1.00±0.02, n = 406) than in the pastoral ranches (0.93±0.02, n = 230, Table 5.4). The number of herbivore species increased significantly with distance from water in the dry season, but in the wet season the number of species did not show a Hippo and livestock grazing, facilitation of other herbivores 79 consistent pattern of variation with distance from water. The number of species increased significantly linearly with distance from water in the ranches but in the reserve it increased between 0 and 0.5 km, declined between 0.5 and 1.5 km and then increased thereafter (Fig. 5.5). Relationship between vegetation structure, predation risk and herbivore biomass Multiple linear regression analysis showed that predation risk was negatively correlated with the percentage cover of grasses shorter than 10 cm (t632 = –3.18; P = 0.001) and between 10 and 30 cm tall (t632 = –3.22; P = 0.001) but positively correlated with the percentage cover of grasses taller than 30 cm (t632 = 2.52; P = 0.011). Multiple linear regression analysis also showed that herbivore biomass was negatively correlated with predation risk (t634 = –6.09; P < 0.001), such that herbivore biomass declined as predation risk increased, implying that herbivores avoided areas dominated by grasses taller than 30 cm. LN (herbivore biomass) 7 Masai Mara National Reserve pastoral ranches 6 Figure 5.4 The distribution of herbivore biomass along distance from water in the Mara Region of Kenya during 2007–2008. Solid and dashed lines denote the Masai Mara National Reserve and pastoral ranches, respectively. 5 4 3 2 1 0 0 0.1 0.25 0.5 0.75 1 1.25 1.5 2 2.5 3 4 5 distance from water (km) Table 5.3 Results of statistical tests of the effects of season, landscape, distance from water and their interactions on aggregate herbivore biomass in the Mara Region of Kenya. NDF is the numerator and DDF the denominator degrees of freedom, respectively. Effects Intercept Season Landscape Distance Season × Landscape Season × Distance Landscape × Distance 80 Chapter 5 NDF DDF MS F P 1 1 1 12 1 12 12 596 596 596 596 596 596 596 4998.00 451.30 172.69 66.45 34.56 26.49 50.66 270.81 24.45 9.36 3.60 1.87 1.44 2.74 <0.001 <0.001 0.002 <0.001 0.172 0.145 0.001 Discussion Hippopotamus and livestock grazing in the Mara influence the structural patterns of vegetation along distance from rivers. Other herbivores attracted to areas close to water and to the short and nutritious grass swards maintained by hippos, exert additional impacts on vegetation structure and basal cover in the piosphere gradients originating from rivers (Butt et al. 2009; Ogutu et al. 2010). Piosphere gradients were not clearly discernible in the pastoral ranches possibly due to the intense and homogenizing effects of livestock grazing (Fig. 5.3; Adler et al. 2001). Hippos extended their grazing range further from water points in dry seasons, likely due to forage depletion near water as the dry season progresses (O’Connor and Campbell 1986), but this seasonal range expansion was more constrained in the pastoral areas where herders graze livestock along rivers in dry seasons, thus depleting vegetation and interfering with hippo ranging pattern from water (Belsky 1999; Thrash 2000). An earlier record of hippo grazing range along the Mara river, north of the SNP in the species richness (no. species) 1.3 Masai Mara National Reserve pastoral ranches Figure 5.5 The distribution of large herbivore species richness (number of different species) along distance from water in the Mara Region of Kenya during 2007–2008. Solid and dashed lines denote the Masai Mara National Reserve and pastoral ranches, respectively. 1.2 1.1 1.0 0.9 0.8 0.7 0 0.1 0.25 0.5 0.75 1 1.25 1.5 2 2.5 3 4 5 distance from water (km) Table 5.4 Results of statistical tests of the effects of season, landscape, distance from water and their interactions on large herbivore species richness in the Mara Region of Kenya. NDF is the numerator and DDF the denominator degrees of freedom, respectively. Effects Intercept Season Landscape Distance Season × Landscape Season × Distance Landscape × Distance NDF DDF MS 1 1 1 12 1 12 12 596 596 596 596 596 596 596 544.39 4.67 0.66 0.57 0.06 0.27 0.49 F 3347.31 28.7 4.04 3.53 0.35 1.68 3.01 P <0.001 <0.001 0.044 <0.001 0.553 0.068 <0.001 Hippo and livestock grazing, facilitation of other herbivores 81 1970s, of 1.5 km (Olivier and Laurie 1974), was smaller than the present estimate of 4 km, suggesting that the recent dramatic increase in the population of Mara hippos (Kanga et al. 2011) or the progressive compression of hippo distribution by changing land use over the last three decades and competition with livestock and other herbivores along the riparian-edge habitats (Reid et al. 2003), probably compel hippos to travel further from water to satisfy their forage requirements. Unlike in the pastoral ranches, a sacrificial zone with heavily depleted grass cover due to repeated grazing and trampling by hippos leaving and returning to water (Thrash and Derry 1999) was well established in the MMNR and extended for about 250 m from river banks. This area was characteristically denuded, had the highest number of hippo trails and the highest percent cover of short grasses and forbs. However, the pastoral ranches had a higher percent cover of bare ground than the MMNR beyond 750 m from water, which can be attributed to impacts of heavy grazing and trampling by large numbers of livestock (Fig. 5.3A). Therefore, differences in their grazing strategies may explain the contrasting impacts of hippo and livestock grazing on patterns of variation in vegetation structure and cover along gradients extending away from riparian habitats in the Mara. We found that close to water, grass was very short in both landscapes, and that this short grass cover declined progressively with increasing distance from water in the MMNR but remained high in the pastoral areas up to 5 km from water, thus signifying the effects of heavy livestock grazing in the pastoral ranches. The shifting mosaics of short grass lawns interspersed with patches of medium and tall grasses were characteristically evident within 2.5 km from water in MMNR and can be attributed to hippo grazing, as this distance corresponds to the active grazing range of hippos from water. These mosaics of short grass lawns are well recognized for their high quality-forage (McNaughton 1983; Fryxell 1991; Adler et al. 2001; Olff et al. 2002). In contrast, vegetation cover in the pastoral ranches was dominated by homogenous short grasses, often shorter than 10 cm, associated with intense and sustained livestock grazing (Fig. 5.3B). Although grazing kept grass height relatively low, grasses still constituted the main fraction of herbaceous cover. Spatial heterogeneity of vegetation increases with patch grazing and decreases with homogeneous grazing (Adler et al. 2001), and influences how herbivores utilize landscapes, especially in areas where forage and water availability are major limiting factors, such as the Masai Mara. Our results show that herbivore dung, biomass and species richness were significantly higher during the dry than the wet season, implying that forage and water are more heavily utilized during dry seasons in Mara. Furthermore, herbivores utilized the MMNR more during the dry season, because they are excluded from the pastoral areas by heavy livestock grazing at this time, and because of the influx of enormous herds of migratory wildebeest, zebra and Thomson’s gazelles. Herbivore biomass and species richness were higher in the MMNR than the pastoral areas, with quadratic distribution 82 Chapter 5 patterns from water apparent in the MMNR and linear patterns evident in the ranches (Fig. 5.4 and 5.5), implying that herbivores were more repelled from water points in the pastoral ranches. We postulate that the effects of shifting mosaics of grazing lawns maintained by hippos improve quality of available forage close to water that attract herbivores in the MMNR riparian-edge habitats (McNaughton 1983; Owen-Smith 1988; Fryxell 1991; Eltringham 1999; Adler et al. 2001; Olff et al. 2002; Arsenault and Owen-Smith 2002; Verweij et al. 2006; Van Wieren and Bakker 2008). In contrast, the intense and homogenous livestock grazing in the pastoral ranches limit forage intake by herbivores (Arsenault and Owen-Smith 2002; Verweij et al. 2006), and repel herbivores from water points. Ultimately, continued sedentarization of pastoralists in the Mara region will progressively exclude herbivores and other wildlife from the pastoral areas of the Mara, similar to patterns reported for other parts of Masailand (Western et al. 2009; Msoffe et al. 2011). High vegetation cover limits the ability of herbivores to scan their surroundings, but also provide good concealment cover for ambush predators (Hopcraft 2002; Verdolin 2006; Hopcraft et al. 2010). Our results demonstrate that herbivores were more abundant in areas of short to medium grass swards, than in areas dominated by tall grasses and hence associated with higher predation risks. This may imply that herbivores were avoiding areas of tall grasses, not only because these areas are of lower forage quality but also because of the increased risks of predation. Specifically, predation risk was lower in areas dominated by grasses shorter than 30 cm but higher in areas dominated by tall grasses, implying that areas with mosaics of short grass lawns maintained by hippo grazing likely reduced predation risk. Therefore, loss of keystone species like hippopotamus may adversely impact the integrity of ecosystems and their services (Coppollilo et al. 2004) Hippopotamus and other herbivores are apparently able to spread impacts of their grazing in the MMNR and sustain characteristic patterns of distribution of vegetation structure and cover, enabling them to access more forage resources through the dry season (Arsenault and Owen-Smith 2002). This could explain the higher herbivore biomass and species richness we recorded in the MMNR. In contrast, the pastoral ranches experience year-round intense livestock grazing, resulting in homogenous short grasslands, thus amplifying competition for forage and water in areas accessed by pastoralists, including parts of the MMNR, especially during dry periods. The grazing gradients from riparian-edge habitats in the MMNR revealed by this study are consistent with findings of other studies conducted elsewhere in piospheres (Andrew 1988; Perkins and Thomas 1993; Thrash and Derry 1999), but were hardly evident in the pastoral ranches. Our results thus demonstrate conspicuous differences in the effects of hippopotamus and livestock grazing, with hippo grazing enhancing spatial heterogeneity of vegetation which, in turn, attracts a rich herbi- Hippo and livestock grazing, facilitation of other herbivores 83 vore assemblage, whereas livestock grazing homogenizes landscapes and repel wild herbivores, especially from water sources. Acknowledgements We thank Charles Matankory and Sospeter Kiambi for assistance with field work and for arranging field logistics. We also thank the Kenya Wildlife Service rangers for providing security during field work, wardens of the Masai Mara Reserve and the management of the Koyiaki and Lemek pastoral ranches for allowing us unlimited access to the study area. EK was supported by the Netherlands Fellowship Program (NFP) and the University of Groningen through the Government of Kenya and by the Frankfurt Zoological Society (FZS). 84 Chapter 5 Hippo and livestock grazing, facilitation of other herbivores 85 Chapter six 6 Hippopotamus as agents of change on riparian-edge communities: A synthesis Introduction Hippopotamus are semi-aquatic herbivores, and water, in which mating, playing, fighting and defecation all takes place, is at the centre of their social life. That is probably why hippopotamus means “river horse” in the ancient Greek language. Hippos also require an open terrestrial grazing land, where their grazing range is limited to grassland mosaics within immediate reach of water. This is a unique lifestyle compared to other grazing herbivores. Due to their large size, habitat and food requirements, hippos tend to have substantial impacts on riparian communities. Their grazing strategies and physical alterations to the environment affect plant and wildlife community compositions in areas they frequently graze (Thornton 1971; Lock 1972; Eltringham 1999). Due to their high dependence on water, their fortunes fluctuate along with those of the water and the wetlands they depend on (Klingel 1995). Despite our knowledge that hippos require water and wetlands for survival, and that wetlands are severely threatened, research on hippopotamus is rare in Kenya. Therefore, this thesis sought to address an important knowledge gap, by studying the nature and dynamics of human-hippo conflicts throughout Kenyan wetlands to understand the challenges facing the conservation of this unique herbivore, under changing land-use and increasing anthropogenic impacts on wetlands; long-term hippo population dynamics in a premier conservation estate in Kenya and East Africa, the Masai Mara. Furthermore, we analyzed the impact and consequences of hippo grazing on vegetation and other herbivores in riparian-edge habitats of the Mara and how these are modified by land use and seasonality in rainfall. Insights into the ecology of hippopotamus Wildlife population size estimates are central to conservation and management of biological diversity. Counting animals, however, can be difficult as some animals are on the move and many others actively avoid human counters, complicating detection and accurate counting. Consequently, we are rarely in a position to obtain absolute total counts in the wild. In studying the hippopotamus population in the Mara Region of Kenya, we established that our 2006 census is the first detailed and complete count for hippopotamus along the Kenyan section of the Mara River system (Chapter 3), although other counts provide good general references. Results from our count showed that there are over 4,000 hippos in Mara and this may be one of the largest single hippo population in Kenya. Thus the Mara is an important hippo conservation stronghold in Kenya and currently holds about 3% of the African hippopotamus population. Our experience from the census is that hippos are usually submerged and do not synchronise their surfacing, thus there are high 88 Chapter 6 density (no./km river) 40 Masai Mara National Reserve pastoral ranches 30 R2 = 0.980 20 10 Figure 6.1 Dramatic increases of hippopotamus densities in the Mara Region of Kenya during 1958 to 2006. Diamond and pyramid marks denote MMNR and pastoral ranches respectively. 0 1960 1970 1980 1990 2000 2010 chances of undercounting during ground censuses as hippos actively avoid counters. However, more accurate numbers can be obtained if individuals and groups are in shallow water and pools. Our results demonstrate that the Mara hippo population density dramatically increased during 1958 to 2006 (Fig. 6.1) and that hippos spatially expanded their range into the pastoral ranches, suggesting that the community pastoral ranches provide important habitats for hippos in the Mara. Smuts and Whyte (1981) describe the reproductive strategy of the hippo as one well adapted to the semi-arid environments, such that when resources are limiting, populations are able to maintain stable populations by delayed sexual maturity and fecundity and so adjust to the carrying capacity of the environment; equally, populations are capable of rapid increase when resources become abundant. Surprisingly, our results reveal considerable increases in hippopotamus numbers and range expansions, while hydrological investigations showed that between 1973 and 2000, the Mara River flow regimes changed drastically, with sharp increases in peaks, attenuated hydrographs and reduced base flows (Mutie et al. 2005), that unfavorably affected shelter and day living space for hippos (Mati et al. 2008). In addition, Oliver and Laurie (1974) and Tembo (1987) suggest that shelter and day-living space generally regulate hippopotamus populations. Therefore, our census results have important implications for hippopotamus ecology, because, contrary to these suggestions, the Mara hippo population dramatically increased during 1970 to 2006 when their shelter and day-living spaces were reasonably unstable. The only plausible explanation that we can put forward for this situation is that the Mara has relatively abundant and sufficient forage (O’Connor and Campbell 1986; Boutton et al. 1988; Onyeanusi 1988), which may outweigh the limitation imposed by deteriorating shelter and day-living space. However, it is evident that the massive destruction of the Mau Forests which forms the catchment of the Mara River and the spiralling extraction of water for irrigations and expansion of settlements, all of which combine to reduce the quantity and quality of water in the Mara River will, Synthesis 89 unless regulated, certainly reduce hippo range in the Mara and probably also their abundance. The spatial range expansion for hippos recorded in Chapter-3 further reveals that the occupation of Keekorok pool and the Mara River outside MMNR are new colonisation events which occurred after 1982. The nearest hippo groups to Keekorok pool are at Mara Bridge, a distance of over 25 km, while the colonised range along Mara River is over 60 km upstream into the pastoral ranches. This demonstrates a remarkable capacity of the common hippopotamus to disperse to new localities. The length of the Mara River that was covered during the count is 99 km (53.3 km in MMNR and 45.7 km in the pastoral ranches). Using the identified hippo grazing range lengths (Chapter 4 and 5), we estimate the hippo grazing area at 426.4 km2 and 274.2 km2, for the MMNR and pastoral ranches, respectively, resulting in a nocturnal terrestrial feeding density of 4.51 hippos/km2 in the MMNR and 5.73 hippos/km2 in the pastoral ranches during dry seasons. However, during the wet seasons, hippos ranged shorter distances, shifting their nocturnal terrestrial feeding density upwards to 7.22 hippos/km2 in the MMNR and 6.87 hippos/ km2 in the pastoral ranches. An interesting question then is whether the Mara is overpopulated with hippos? Interestingly, the present hippo densities have not changed much from the 5 hippos/km2 recorded in the MMNR in 1970 (Olivier and Laurie 1974), and are similar to 4.5 hippos/km2 recorded in Liwonde National Park, Malawi in 2002/2003 (Harisson et al. 2007), 4 hippos/km2 reported for Luangwa River, Zambia in 1982/1983 (Tembo 1987) but are lower than the 28 hippos/km2 reported for Queen Elizabeth National Park, Uganda between 1963 to 1967 (Field and Laws 1970). It is therefore well possible that Mara can hold more hippos than it supports at present. Ecological influences of hippopotamus within Mara riparian-edge community Hippopotamus grazing pressure transforms tall grasslands into a shifting mosaic of short, medium and tall grass patches, and they maintain the short grass swards through repeated and continuous grazing. This is demonstrated by our results in Chapter 4 and 5, in which areas within the MMNR where hippos are the main resident grazers, the spatial distribution of their grazing lawns contributes significantly to structural diversity of vegetation within the strip of 0-3 km from rivers (Fig. 6.2, O’Connor and Campbell 1984). Although McNaughton (1984, 1985) notes that large herds of migratory mesoherbivores create and maintain grazing lawns, our results suggest that hippos have superior effects on lawn formation and maintenance within the riparian-edge habitats. Our suggestion is supported by the fact that even with over one million immigrant mixed herds of wildebeest, zebra and 90 Chapter 6 river/water point ; ne zo e g, s ific lin re cr mp ivo , Sa tra rb ne zo he all ion a t of d iliz cs n ut sai m a es po mo diu tch hip ith me pa ne gh w rt, ass zo o r Hi sh ll g ion ed s at ix ore ta iliz m iv ut by erb po zed oh hip utili mes w t Lo bu s of rd he Vegetation is destroyed' forbs and bare ground cover dominate, with noticeable invasive/ weedy/annual species 250 m Lawns and heavily grazed grass/forbs mixture, with noticeable woody species recruit and establish 3500 m Tall grasses, accumulated biomass, minimal forbs and woody species gets rare 5 0 00 m Figure 6.2 Hippopotamus grazing in the MMNR, diversify vegetation structure and enhance spatial heterogeneity by creating and maintaining mosaics of short and medium grass patches. Thomson gazelle in the Mara during the dry season, evidence of grazing lawns was only clear within the 3 km strip zone from rivers, a zone that correspond with hippo grazing range (Chapter 4 and 5), notwithstanding the fact that the mixed herds of mesoherbivores freely grazed beyond the 3 km hippo range from rivers. There are many other factors influencing vegetation structures in the Mara, but our results show that hippopotamus grazing has distinct impacts at the riparian-edge habitat patch level. This finding guides us to conclude that hippopotamus is a keystone ecosystem engineer able to profoundly modify ecosystems and facilitate other herbivores in the Mara (Owen-Smith 1987) in ways that even large herds of mesoherbivores cannot. Hippos establish a well-developed pathway network for exit and entry into water and for accessing their grazing range. Their trampling effects at riverbank exits cause considerable increase in bare ground, which, in addition to the denuded trails, accelerate soil erosion (Thornton 1971; Lock 1972). Furthermore, the shortgrass grazed areas decrease available combustible biomass, promoting their invasion by woody species (Fig. 6.2, Fig. 6.3, and Chapter 4 and 5). The effects of hippopotamus grazing on soils, plants and other herbivores was most pronounced immediately at the riverbanks due to their trampling effects (the ‘piosphere’ effect, Lange 1969) and at intermediate distances from rivers (Fig. 6.3). Hippo-grazing effects enhanced vegetation structural diversity and improved spatial heterogeneity associated with the riparian zone, and thus enhanced species diversity and caused Synthesis 91 mosaic of short, medium and tall grass patches zone grass height/biomass relative measure predation risk grass quality Figure 6.3 Effects of hippopotamus grazing on the quality and quantity of grass with distance from rivers in Mara and its associated influence predations risk to mesoherbivores. edge of hippo grazing range distance from rivers compositional shifts in both plants and herbivores at intermediate distances from rivers within the MMNR (Chapter 4 and 5). However, grazing effects of mesoherbivores and livestock did not achieve similar outcomes. Heavy grazing by livestock in the pastoral ranches reduced the quality and quantity of forage and vegetation cover, and further adversely affected plants and herbivore species richness, abundance and composition. Sedentarization of the pastoral Maasai in the Mara has resulted in year-round congregation of livestock around water sources, which clearly reduces standing biomass and herbaceous species diversity, thus reducing the ability of the pastoral ranches to support diverse wildlife assemblages. Threats to hippopotamus The common hippopotamus’ population in Africa declined due to habitat loss, exploitation and conflicts with people by 7-20% during 1996 to 2004, and the current population is likely between 125,000 and 148,000 hippos in the wild (Lewison and Oliver 2008). Unfortunately, detailed information on hippopotamus population trends and associated threats are lacking in Kenya. However, results in Chapter 2 and 3 show numerous threats to hippopotamus conservation across Kenya and the major threats include declining habitats and range, incompatible land uses, land-use changes and conflicts with people. In the Mara region, deforestation, agricultural expansion and intensification (including irrigation) and expansion of human settlements, have negatively affected the hydrologic, physical and social aspects of the Mara River Basin (IUCN 2000; Gereta et. al. 2002; Mati et al. 2008), with potentially adverse consequences for the Mara River hippopotamus population. Although this thesis did not directly quantify threats to hippos in the Mara, it is probable that changes in the hydrological cycles of the Mara River could reduce the hippo range and hence also their abundance. This bleak scenario is repli- 92 Chapter 6 cated in many other Kenyan wetlands (Crafter et al. 1992), which are important for hippopotamus conservation. Human-hippo conflicts pose an important threats and challenges to hippo conservation endeavors in Kenya, especially with increasing pressures on wetlands and a realization that a substantial number of hippos inhabit wetlands that often extend outside of protected areas, into the agricultural landscapes, thus increasing interactions between people and hippos. Consistent with these increased interactions, human-hippo conflicts have increased in space and time in Kenya (Chapter 2). These conflicts are not likely to decline and may in fact be intensifying as increasing human population and land-use changes impact more adversely on wetlands. However, historical records show that hippos have long been a problem to rural farmers in various parts of Kenya and were accorded official protection in the 1920s to reduce their persecution (Kenya Game Department 1953). We analyzed the nature, intensity, seasonality, spatial and temporal patterns in human-hippo conflict incidences reported from wildlife stations Kenya-wide, over a 12-year period spanning 1997-2008, and established that human-hippo conflicts indeed increased 26-fold. Hippos killed 67 and injured 88 people, in addition to being involved in 47 incidences of livestock attacks. In retaliation, 522 hippopotamus were killed as a problem animal control strategy by wildlife mangers. Based on the Kenya Wildlife Service 8-Conservation Regions across Kenya then, our results show that 50% of these regions experienced considerable increases in conflicts over time. This dramatic rise in human-hippo conflicts in Kenya is a consequence of both natural and human-mediated disturbances on hippo habitats including wetlands (Crafter et al. 1992). Hippopotamus habitat losses have accelerated through conversion of hippo grazing ranges into agricultural use, while aquatic refugia are diminished by irrigation and other human activities along riverine systems (Eltringham 1999; Smuts and Whyte 1981). The high frequency of crop raiding behavior shown by hippos is construed to indicate increasing agricultural expansion on wetland habitats in Kenya. However, the high lose of hippos through unregulated problem animal control measures, is of conservation concerns. Illegal hunting (poaching) of hippopotamus is rare in Kenya, but in the rest of Africa, poaching of hippos is mostly done for meat though there is increasing demand for hippo canine teeth (Weiler et al. 1994), the ivory of which is considered better quality than that of the elephant. If trade in hippo teeth develop and thrive, then hippopotamus will be at serious risks (Eltringham 1993). Concluding Remarks In this thesis, I show that hippos increased dramatically in numbers and extended their range in the Mara against a background of deteriorating habitat conditions Synthesis 93 related to recurrent droughts, rising temperatures and progressive habitat desiccation and fundamental land use changes, implying that hippos can increase rapidly even in a context of considerable climatic variability. However, it is certain that anthropogenic land-use changes affecting the Mara River and its hydrological cycles may constrict the Mara hippo population range and possibly reduce their abundance. The hippo census was very challenging and further investigations should focus on how to improve census techniques for hippopotamus. Our results indicate that ecological processes or habitat characteristics associated with hippo grazing structure plant species richness and composition and the distribution of other herbivore along riparian-edge habitats. Plant species richness and composition varied along the hippo-grazing gradient from rivers, partially in response to spatial heterogeneity of vegetation structure resulting from hippo grazing activities. Consequently, hippos facilitated grazing by mesoherbivores and enhanced co-existence of plant species, thereby promoting species diversity. Therefore, along the riparian-edge habitats the hippopotamus is an important ecosystem engineer and a keystone herbivore, creating and maintaining shifting mosaics of grazing lawns, an ecosystem function that was not effectively performed by large herds of grazing mesoherbivores. 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References 109 Summary Samenvatting Summary Samenvatting Executive summary African savannahs are endowed with a high diversity and abundance of large mammalian herbivores but increasing degradation, fragmentation and loss of wildlife habitats particularly in rangelands primarily to cultivation and settlements due to human population growth and development is accelerating wildlife population declines. The expansion of settlements and cultivation has had a major adverse effect on the distribution and abundance of wild herbivores, both at the population and community levels. One such herbivore species is the common hippopotamus, commonly referred to as “hippo”. Hippos have featured in human affairs since at least the time of the Egyptian Pharaohs, where they were venerated as gods and have been portrayed in art down the ages. Primary threats to hippopotamus conservation include the loss of essential grazing lands to cultivation, settlements, illegal harvests for bushmeat and canine teeth ivory trade, retributive killings for destroying crops and growing pressure on fresh water resources, leading to the loss of their prime habitats. Ultimately, the reliance of hippos on fresh water habitats puts them at odds with increasing human populations, exacerbating their vulnerability. Due to increasing human population and agricultural expansion and development in and around wetlands, hippos often run into frequent conflicts with people. The protection of riparian and wetland habitats and control of poaching of hippos are therefore two pressing challenges facing contemporary hippo conservation efforts, as are measures to prevent the drying-up of water courses due to deforestation, spiraling water extraction and global warming and loss of riparian-edge grazing grounds. Hippopotamus are classified together with elephant, rhinoceros and giraffe as “megaherbivores”, a select group of terrestrial plant-feeding mammals with a body mass in excess of 1,000 kg. The very large body size has fundamental consequences for the ecology of this group that sets them apart from other herbivores. Megaherbivores are generally threatened throughout their historic distributional ranges, and their continued survival is precarious as their expansive habitat requirements often brings them into direct conflicts with rising human populations. Nonetheless, hippopotamus differ from the other megaherbivores in having a dual requirement of a day-living space in water and an open grazing range often visited at night. This requirement greatly affects the manner in which hippos utilize resources and survive in landscapes dominated by high human population densities and continuous land use changes. Recent estimates covering 1996 to 2004, suggest that about 125,000 -148,000 hippos occur in fragmented populations in rivers, lakes and other wetlands of 36 African countries, of which 20 countries have confirmed declining populations, seven have populations of unknown status, nine have stable populations and three (Algeria, Egypt and Mauritania) have experienced recent extinctions. Based on this estimated global population, coupled with intensifying 112 Summary conservation threats, the hippopotamus was categorized as Vulnerable on the IUCN Red List in 2006. Despite its imposing size, Vulnerable status and grazing impacts on riparian habitats, and rising conflicts with people, the hippopotamus has not been well studied or monitored in many parts of its range, including Kenya where the species has been officially protected since the 1920s. Yet, monitoring of hippopotamus is necessary to understand the factors under-pinning its population dynamics and hence to develop an understanding of how the hippos influences, and are influenced by changes in riparian habitats and how they respond to land-use changes, climate change and variability, and conflicts with humans. Thus, in this thesis, I sought to fill these glaring gaps in our knowledge, to inform efforts aimed at addressing the ongoing shifts in human disturbance regimes on riparian-edge habitats and their consequences for hippopotamus conservation. Consequently, the prime aim of this thesis was to analyze (1) human-hippo conflicts in Kenya over the 12-year period covering 1997–2008, (2) hippo population dynamics in the Mara region of Kenya during 1958–2006 and (3) the patterns and consequences of hippo and livestock grazing in the riparian habitats of the Mara on vegetation structure, species richness and composition and herbivore abundance and species diversity under protection and pastoralism. The riparian habitats of the Mara River Basin that cover some 13,750 km2, situated in southwestern Kenya and in northern Tanzania formed the centerpiece of this thesis. In the thesis, I start by presenting a detailed review of contemporary hippo conservation and management efforts in Kenya. I then examine key management issues on human-hippo conflicts, identifying the extent, severity and distribution (spatial and temporal) of hippo-related damages to crops and how retaliatory killings of hippos are undermining conservation efforts in Kenya (chapter 2). I assembled and analyzed a national human-hippo conflict data collected by the Kenya Wildlife Service, covering a12-year period spanning 1997-2008, and established that human-hippo conflicts increased 26-fold Kenya-wide in this period. This dramatic rise in human-hippo conflicts is a consequence of both natural and human-mediated disturbances on hippo habitats, including wetlands. These conflicts are not likely to decline any time soon, and are likely intensifying, as increasing human population and land-use changes impact more adversely on wetlands, portending a precarious future for hippos outside Kenyan protected areas. I further explored the population status of hippopotamus at one of Kenya’s premier conservation estates, the Masai Mara, where I surveyed and counted hippopotamus along 155.3 km of the Mara river system (chapter 3). I compared the survey results with those of previous surveys and revealed how hippopotamus populations surprisingly increased rapidly and expanded their range in a context of considerable climatic variability and against a background of deteriorating habitat conditions over a period of 35 years covering 1970 to 2006. I concluded that Summary 113 increased anthropogenic activities, especially land-use changes on the group ranches surrounding the world-famous Masai Mara National Reserve and destruction of the Mau catchments of the Mara River, unless regulated, will continue to adversely affect the hippopotamus population, with significant spill-over effects on other mammalian grazers dependent on grazing lawns created and maintained by hippopotamus. When occurring at high densities, hippos can extensively damage rangelands through sustained grazing and trampling. However, there is a great deal of debate and controversy as to whether hippopotamus impacts on riparian vegetation structure and other ecosystem processes should be regarded as undesirable, or whether they are reversible states whose trajectories are governed by fluctuations in hippopotamus population sizes. Central to this debate and resolving this controversy is the identification of appropriate benchmark states characterizing the vegetation states prior to local colonization by hippos or extirpation of hippo populations (chapter 4). In a field experiment, I investigated the interactive effects of hippopotamus and livestock grazing on vegetation structure, plant species composition and richness and herbivore abundance and species diversity in the protected Masai Mara National Reserve and its adjoining pastoral lands. I demonstrated the important engineering impacts of hippopotamus on vegetation that facilitates the establishment and co-existence of myriads of plant species, culminating in enhanced species richness in areas experiencing intermediate grazing levels, especially within the protected landscape. Hippopotamus grazing activities created and maintained a shifting mosaic of patches of differentiated vegetation structure, enhancing structural heterogeneity of vegetation and attracting a diverse and abundant herbivore assemblage at intermediate distances from rivers, thus facilitating riparian-edge habitat use by other wild herbivores (chapter 5). In conclusion, I synthesize the key results of this thesis and discuss the conservation status of hippos in Kenya and the ecological role of hippos along riparianedge habitats (chapter 6). The results of this thesis on the effects of hippopotamus on the vegetation structure, plant species composition and richness, clearly points to a keystone role for hippos. Further, these results confirm that hippopotamus affect a number of ecosystem-level functions and that their influence on other herbivores may be much more important than has been appreciated previously. Plant species composition and richness patterns were variable between hippopotamus and livestock-dominated landscapes but different factors were driving species composition between the two landscapes. The abundance and species richness of the other herbivores were consistently higher on the hippopotamus dominated landscape. I suggest that hippopotamus provide some unique ecosystem engineering functions not duplicated by mesoherbivores along riparian-edge habitats. Consequently, any significant decline of hippopotamus populations in the Serengeti-Mara ecosystem and elsewhere in African savannas may precipitate 114 Summary considerable erosion of habitat heterogeneity within riparian-edges and the unique biological diversity they support. From a practical hippopotamus conservation perspective, I recommend the urgent preparation and implementation of a management plan for Kenyan hippos, establishment of effective Kenya-wide programs to protect hippos from the bushmeat and canine teeth ivory trade and retaliatory killings and effective monitoring and reporting of hippo-human conflicts for timely identification of hotspots of conflicts and targeted remedial interventions throughout Kenya. I further recommend that urgent steps be taken to alleviate the degradation, fragmentation and loss of hippo habitats in Kenya, especially in regions experiencing increasing human and livestock numbers and expanding settlements, cultivation and other land use changes, yet supporting substantial hippo populations. Summary 115 Samenvatting Afrikaanse savannes worden gekenmerkt door een hoge diversiteit en abundantie van grote herbivore zoogdieren, maar leiden in toenemende mate aan degradatie, fragmentatie en verlies van habitats met name in en rond natuurgebieden. De uitbreiding van nederzettingen en de landbouw heeft een grote negatieve invloed op de verspreiding en de abundantie van wilde grazers, zowel op het niveau van de populatie als op het niveau van de levensgemeenschap. Een van deze grazende soorten is het nijlpaard. Nijlpaarden zijn in interactie met mensen tenminste sinds de tijd van de Egyptische farao's, waar ze werden vereerd als goden en zijn geportretteerd in de kunst door de eeuwen heen. Primaire bedreigingen voor de instandhouding het nijlpaard zijn onder andere het verlies van essentiële weidegronden door uitbreiding van de landbouw, nederzettingen, illegale oogsten voor bushmeat en ivoor, ‘wraak’ moorden voor de vernietiging van gewassen en toenemende druk op de zoetwatervoorraden, wat leidt tot het verlies van hun primaire habitat. Ten slotte zet de reputatie van nijlpaarden ze op gespannen voet met de toenemende dichtheden van mensen, wat hun kwetsbaarheid verergert. Door de toenemende menselijke bevolkingsdichtheid en uitbreiding van de landbouw en de ontwikkeling in en rond waterrijke gebieden, komen nijlpaarden vaak ook in conflicten met mensen. De bescherming van de oevers van rivieren en wetland-habitats en de controle op het stropen van nijlpaarden zijn dus twee hedendaagse uitdagingen belangrijk voor instandhouding van de nijlpaarden populaties, evenals maatregelen ter preventie van het opdrogen van waterlopen als gevolg van ontbossing, de stijgende waterwinning en opwarming van de aarde, en degradatie van habitats langs rivieren. Nijlpaard worden samen met olifanten, neushoorn en giraf gezien als "megaherbivoren", een selecte groep van terrestrische herbivore zoogdieren met een lichaamsgewicht van meer dan 1.000 kg. De zeer grote lichaamsgrootte heeft fundamentele gevolgen voor de ecologie van deze groep die hen onderscheidt van andere planteneters. Megaherbivoren zijn over het algemeen bedreigd, en hun voortbestaan is onzeker sinds hun specifieke habitat eisen hen vaak in direct conflict brengen met de groeiende menselijke bevolking. Niettemin, verschilt het nijlpaard van de andere megaherbivoren in de dubbele beslag op zowel een dag-leefruimte in water en een open begrazingsgebied dat vaak ’s nachts bezocht wordt. Dit dubbele vereiste is van grote invloed op de wijze waarop de nijlpaarden overleven in landschappen welke wordengekenmerkt door een hoge menselijke bevolkingsdichtheid en continue veranderingen in landgebruik. Uit recente schattingen over 1996 tot 2004 blijkt dat ongeveer 125.000 –148.000 nijlpaarden voorkomen in versnipperde populaties in rivieren, meren en andere watergebieden van 36 Afrikaanse landen, waarvan 20 landen een dalende aantallen nijlpaarden laten zien, zeven landen hebben populaties van een onbekende status, negen landen hebben stabiele popula- 116 Samenvatting ties en in drie landen (Algerije, Egypte en Mauritanië) zijn nijlpaarden uitgestorven. Op basis van deze geschatte wereldpopulatie, in combinatie met intensivering van het behoud bedreigingen, is het nijlpaard gecategoriseerd als ’kwetsbaar’ op de IUCN Rode Lijst in 2006. Ondanks zijn imposante afmetingen, zijn kwetsbare status en zijn begrazingseffecten op oeverhabitats en de groeiende conflicten met mensen, is het nijlpaard niet goed onderzocht in veel delen van zijn leefomgeving, waaronder Kenia, waar de soort officieel is beschermd sinds 1920. Daarom is onderzoek van de nijlpaard noodzakelijk om de oorzaken te begrijpen van populatie fluctuaties en daarmee ook tot inzicht te komen hoe nijlpaarden veranderingen in de oeverstaten habitats beïnvloeden en hoe ze daar zelf door beïnvloed worden en hoe ze reageren op ontwikkelingen en veranderingen in landgebruik, klimaatverandering en variabiliteit, en conflicten met mensen. In dit proefschrift heb ik geprobeerd om deze grote gaten in onze kennis te vullen, om inspanningen gericht op het aanpakken van veranderingen in de menselijke verstoring regimes op oeverhabitats en de gevolgen daarvan voor de instandhouding nijlpaard te faciliteren. Dus voornaamste doel van dit proefschrift was om het volgende te onderzoeken: (1) conflicten tussen mensen en nijlpaarden in Kenia over een periode van 12 jaar (1997–2008), (2) de populatiedynamiek van nijlpaarden in de Mara regio van Kenya tijdens 1958-2006 en (3 ) de patronen en de gevolgen van nijlpaard en vee begrazing in de oeverhabitats van de Mara rivierin Kenia op de vegetatie structuur, soortenrijkdom en de samenstelling, en abundantie en soortenrijkdom van herbivoren, waarbij volledige bescherming is vergeleken met pastoralisch gebruik door Masai herders. De overhabitats van de Mara River Basin , die wel 13.750 km2 bestrijken, en gelegen zijn in het zuidwesten van Kenia en in het noorden van Tanzania, vormen de kern van dit proefschrift. In het proefschrift, begin ik met het presenteren van een gedetailleerd overzicht van de hedendaagse nijlpaard bescherming en de beheersinspanningen ten aanzien van deze soort in Kenia. Vervolgens heb ik belangrijke vraagstukken over menshippo conflicten onderzocht, en de omvang, de ernst en de verspreiding (ruimtelijke en temporeel) van nijlpaard-gerelateerde schade aan gewassen onderzocht en onderzoek gedaan naar hoe ’wraak-moorden’ op nijlpaarden pogingen tot zijn de instandhouding van de soort in Kenia ondermijnen (hoofdstuk 2). Ik analyseer een nationale mens-nijlpaard conflict dataset verzameld door de Kenya Wildlife Service, 12 jaar lang verspreid over 1997–2008, en stel vast dat de mens-nijlpaard conflicten 26-voudig stegen in heel Kenia in deze periode. Deze dramatische toename van de mens-nijlpaard conflicten is een gevolg van zowel natuurlijke als door de mens veroorzaakte verstoring van nijlpaarden habitats, met inbegrip van wetlands. Deze conflicten zullen waarschijnlijk niet op korte termijn afnemen, en zelfs intensiveren, door toename van de menselijke bevolking en veranderingen in landgebruik die vooral negatief uitpakken voor wetlands, wat zorgt voor een onzekere toekomst Samenvatting 117 voor nijlpaarden buiten de Keniaanse beschermde gebieden. Verder heb ik gekeken naar de populatie status van nijlpaarden in één van Kenia’s belangrijkse natuurgebieden, de Masai Mara, waar ik nijlpaarden zocht en telde langs 155.3 km van de Mara rivier (hoofdstuk 3). Ik vergeleek de resultaten van de telling met die van eerdere onderzoeken en heb laten zien hoe nijlpaard populaties verrassend snel stegen tijdens grote klimaatsveranderingen en tegen een achtergrond van verslechterende habitats omstandigheden over een periode van 35 jaar van 1970 tot 2006. Ik concludeerde dat meer menselijke activiteiten, vooral veranderingen in landgebruik op de groep ranches rond de wereld-beroemde Masai Mara National Reserve en de vernietiging van de Mau stroomgebieden van de Mara rivier, tenzij gereguleerd, negatieve invloed zal blijven hebben op de nijlpaarden populatie, met aanzienlijke spill-over effecten op andere grazende zoogdieren die afhankelijk zijn van de ‘grazing lawns’, gemaakt en onderhouden door het nijlpaard. Bij hoge dichtheden kunnen nijlpaarden grote effecten aanrichten in natuurgebieden door aanhoudende begrazing en vertrapping. Er is een controverse over de vraag of nijlpaard effecten op de oevervegetatie structuur en andere ecosysteem processen moeten worden aangemerkt als ongewenst, of dat ze reversibel zijn, waarvan de trajecten worden beheerst door schommelingen in de nijlpaarden populatie. Centraal in dit debat en het oplossen van deze controverse is de goed meting van de uitgangssituatie van de vegetatie voorafgaand aan de lokale kolonisatie door nijlpaarden of voorafgaand aan de uitroeiing van nijlpaard populaties (hoofdstuk 4). In een veldexperiment onderzocht ik de interactieve effecten van nijlpaarden en begrazing door vee op de vegetatiestructuur, de samenstelling van plantensoorten en de soortenrijkdom van planten, en herbivoor abundantie en soortendiversiteit in de beschermde Masai Mara National Reserve en de aangrenzende pastorale gronden. Ik heb aangetoond dat belangrijke ’ecosystem engineering’ effecten van nijlpaarden er voor zorgen dat myriade plantensoorten makkelijker vestigen en coexisteren, zorgend voor een hogere rijkdom aan soorten in gebieden met gemiddelde begrazings niveaus, met name binnen het beschermde reservaat landschap. Nijlpaard begrazings activiteiten creëren en onderhouden een schuivende mozaïeken van patches van gedifferentieerde vegetatie structuur, versterken de structurele heterogeniteit van de vegetatie en ze trekken een gevarieerde en grote herbivoor gemeenschap aan op middelmatige afstanden van rivieren, door het faciliteren van het gebruik van oeverhabitats voor andere wilde herbivoren (hoofdstuk 5). In de synthese bespreek ik de belangrijkste resultaten van dit proefschrift en de beschermings-staat van nijlpaarden in Kenia en de ecologische rol van nijlpaarden langs de oeverhabitats (hoofdstuk 6). De resultaten van dit proefschrift over de effecten van nijlpaarden op de vegetatie structuur, wijst duidelijk op een sleutelrol voor nijlpaarden. Verder bevestigen deze resultaten dat nijlpaarden een aantal ecosysteemfuncties beïnvloeden en dat hun invloed op andere herbivoren veel belangrijker zijn dan eerder werd aangenomen. Samenstelling van plantensoorten 118 Samenvatting en soortenrijkdom patronen verschilden tussen door nijlpaarden en vee begraasde landschappen, maar de abundantie en rijkdom van de andere herbivore soorten werden steeds hoger gevonden in door het nijlpaard gedomineerde landschappen. Ik stel voor dat nijlpaarden een aantal unieke ‘ecosystem engineering’ functies hebben die mesoherbivores langs de oeverstaten-edge habitats niet kunnen bieden. Bijgevolg kan een grote daling van de nijlpaard populatie in het Serengeti-Mara ecosysteem en elders in de Afrikaanse savannes zorgen voor een aanzienlijke verlies van de habitat heterogeniteit binnen riviergebieden-randen en voor een afname van de unieke biologische diversiteit die ze ondersteunen. Vanuit een praktisch oogpunt van nijlpaard bescherming, adviseer ik de dringende voorbereiding en uitvoering van een beheersplan voor Keniaanse nijlpaarden, het opstellen van effectieve Keniabrede programma's om nijlpaarden te beschermen tegen de bushmeat en ivoor handel en de ‘wraakmoorden’ en ik adviseer doeltreffende monitoring en rapportage van nijlpaard-mens conflicten voor de tijdige identificatie van hotspots van conflicten en gerichte corrigerende interventies in heel Kenia. Ik raad verder aan dat er dringend maatregelen worden genomen om de degradatie, fragmentatie en verlies van nijlpaard habitats in Kenia te verlichten, vooral in regio’s waar veel nijlpaarden voorkomen en waar menselijke populaties veestapels en nederzettingen toenemen, en teelt en andere veranderingen in landgebruik momenteel worden uitgebreid. Samenvatting 119 Acknowledgemennts Acknowledgements I am delighted that I have completed my PhD dissertation, but I also want to point out one of the greatest truths of life; that I had munificent goodwill and support along the way. Competent, committed and dedicated individuals gave me their best considerations without reservation. I sincerely thank Prof. Han Olff, my promoter and head of the COCON Research Group who charitably allowed me unlimited freedom in pursuing divergent hippopotamus research ideas but also ensured that I received guidance and supervision. I highly value the supervision, guidance and mentorship that I received from Dr. Joseph Ogutu, whose encouragement and support from the preliminary to the concluding level enabled me to develop philosophical understanding of this dissertation. My field assistant Charles Matankory, is a rare and gifted gentleman who made my field achievements possible and memorable by giving his best enterprises. Anonymous reviewers and contemporaries pleasantly engaged me in lengthy and productive exchanges on hippopotamus ecology, conservation and management, further advancing my philosophy. I humbly shine this dissertation spotlight on you all! Over the 5-years that I was engaged on this dissertation, many friends and colleagues refocused my bearings amid sopping logistical necessities. I am grateful to Joyce Rietveld for happily providing me with detailed RuG orientation procedures from as early as January 2006. Jacob Hogendorf availed to me a much needed bicycle during my RuG visits while Jan van den Burg regularly sorted my RuG IT requirements; these gestures are truly long lasting beyond this dissertation. Inspiring colleagues from the COCON Research Group included Grant Hopcraft, Ciska Veen, Irma Knevel, Roos Veeneklas, Sandra van Graaf and Moses, Nina Bhola, Sanne de Visser, Bernd Freymann, Esther Chang, Cleo Gosling, Fons van der Plas and Jasper Ruifrok among many others. The COCON secretary, Ingeborg Jansen, cheerfully guided me through the concluding logistics for this dissertation’s examination, while Dick Visser expertly prepared the book lay-out and facilitated its printing. Anke Kramer arranged my accommodation at Haren; I greatly appreciate her efforts of making me feel at home away from Nairobi! At the International Livestock Research Institute (ILRI) Nairobi, I was privileged to interact and tap the expertise of Shem Kifugo and Andrew Muchiru. Joseph Mukeka, a colleague at Kenya Wildlife Service (KWS), gracefully availed the much needed ArcGIS tutorials. Many thanks to the numerous vehicle technicians/mechanics at the Sekekani (Masai Mara) garages; they ensured that our revamped landcruiser stayed on the sampling transects even after endless visits to the garages. Truthfully, all these folks form an inspiring trail of friends who in their own deeds, contributed towards this dissertation “Harambee” and I collectively thank them all. Four key institutions supported my undertakings towards this dissertation; the Netherland Fellowship Program (NFP) provided the main financial grant, while additional field support came in hardy from the Frankfurt Zoological Society (FZS). The University of Groningen was my host institution during this dissertation period 122 Acknowledgements and further supplemented my field grant. Kenya Wildlife Service (KWS) gladly released me from official duties to concentrate on this dissertation. Thus, the commitment of these institutions towards my studies truly demonstrates their truthfulness to the famous Chinese saying that “for one year of prosperity, grows grains; for a decade of prosperity, grow trees; but for a future of prosperity, grow people”. While working on this dissertation, I spent long and extended periods away from my family. I highly appreciate my wife Geldine for her patience, tolerance and unwavering support to our family during my absence; her moral support was steamy and she is my best friend ever! My lovely daughters Renne and Krista and son Robin, missed enormous fatherly attention without an option to protest and I thank them too for their patience. Lastly, the completion of this dissertation rekindled memories of the love, support and encouragement that I have endlessly received from my parents, to always be focused, dedicated and disciplined in whatever I do; the concluding moment for this dissertation testifies that I have once again kept that promise! Acknowledgements 123 124 Publication list Kanga, E.M., Ogutu, J., Hans-Peter, P. and Olff, H. (2011). Hippopotamus and livestock grazing: influences on riparian vegetation and facilitation of other herbivores in the Mara Region of Kenya. Journal of Landscape and Ecological Engineering, DOI: 10.1007/s11355-011-0175-y Kanga, E.M., Ogutu, J., Hans-Peter, P. and Olff, H. (2011). Human-hippo conflicts in Kenya during 1997-2008: Vulnerability of a megaherbivore to anthropogenic land use changes. Journal of Land Use Science, DOI: 10.1080/1747423X.2011. 590235 Kanga, E.M., Ogutu, J.O., Olff, H. and Santema, P. (2011). Population trend and distribution of the Vulnerable common hippopotamus Hippopotamus amphibius in the Mara Region of Kenya. Oryx, 45: 20–27. Reed, D., Kanga, E.M. and Behrensmeyer, A.K. (2006). Plio-Pleistocene paleoenvironments at Olduvai based on modern small mammals from Serengeti, Tanzania and Amboseli, Kenya. Journal of Vertebrate Paleontology, 26(3):114A. Kanga, E.M. (2003). Ecology and Conservation of duikers in Arabuko-Sokoke Forest Reserve, Kenya. In: Ecology and Conservation of small antelopes (eds A.B. Plowman) pp 155-156. Furth: Filander Verlag. Kanga, E.M. (2001). Survey of Black and white colobus monkeys Colobus angolensis palliatus in Shimba Hills National Reserve and Maluganji Sanctuary, Kenya. American Society of Primatology Bulletin, 25: 8–9. Kanga, E.M. and Heidi C.M. (2000). The status of Angolan black and white colobus monkeys Colobus angolensis palliatus in Diani forests, Kenya. African Primate, 4: 50–54. Kanga, E.M. (2000). Survey of Aders’ duiker Cephalophus adersi in Zanzibar, Tanzania. Gnusletter, 19: 6–9. P.le F.N. Mouton, A.F. Flemming and E.M. Kanga (1999). Grouping behavior, tailbiting behaviour and sexual dimorphism in the armadillo lizard Cordylus cataphractus from South Africa. Journal of Zoology, 249: 1–10. Kanga, E.M. (1995). Preliminary survey of Aders’ duiker Cephalophus adersi in Arabuko-Sokoke Forest Reserve, Kenya. Gnusletter, 14: 7–10. 125 Affiliation of Co-Authors drs. Peter Santema, Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK. Dr. Joseph O. Ogutu, Universitaet Hohenheim, Institute of Crop Science, Bioinformatics Unit, Fruwirthstrasse 23, 70599 Stuttgart, Germany. Prof. Hans-Peter Piepho, Universitaet Hohenheim, Institute of Crop Science, Bioinformatics Unit, Fruwirthstrasse 23, 70599 Stuttgart, Germany. Prof. Han Olff, COCON-CEES, University of Groningen, Centre for Life Sciences, Postbox 11103, 9700 CC Groningen, The Netherlands. 126 Curriculum Vitae Erustus M. Kanga Key Qualifications: Natural Resources Conservation and Management; Ecology and conservation of tropical forests, savannahs, wetlands and threatened species therein, with emphasis on research addressing links between species and ecosystem, focusing on anthropogenic interactions; Climate change vulnerability assessment and mapping. Education background 2006 – 2011 PhD degree, University of Groningen, Netherlands Thesis title: “The Kenyan Hippo: Population dynamics, impacts on riparian vegetation and conflicts with humans” 1997 – 2000 MSc degree in Biology of Conservation, University of Nairobi, Kenya. Thesis title: “Some Ecological aspects and Conservation of duikers in Arabuko-Sokoke Forest, Kenya” 1990 – 1994 BSc degree (hon.) in Wildlife Management, Moi University, Kenya Specialized skills • Certified and Registered by the National Environment Management Authority (NEMA) Kenya, as a Lead Expert on matters of Environmental Impact Assessments (EIA) and Environmental Audits (EA). Professional Experience 1. Natural Resources Conservation - Kenya Wildlife Service (KWS) i. 2011 – Present: Assistant Director for Ecosystems and Landscape Conservation Department. ii. 2006 – 2011: Assistant Director for Ecological Monitoring & Biodiversity Information Management Department. iii. 2005 – Personal Assistance to Director (PAD); played a key-supporting role to the Director, as he discharged his corporate mandate. iv. 2004 – Senior Scientist heading Mweiga Research Station; responsible for provision of leadership to a multi-disciplinary team in the formulation of biodiversity conservation strategies and the development of integrated management plans for Aberdare and Mt. Kenya Forest ecosystems and the Mwea National Reserve. v. 2002 – 2003: Research Scientist heading the Ecological Monitoring Unit; responsible for executing and compiling information on ecological monitoring programs and biodiversity inventories for Kenya’s protected areas. vi. 2000 – 2001: Assistant Research Scientist for Ecological Monitoring. 2. Assistant Research Scientist - National Museums of Kenya (1997 – 2000). Centre for Biodiversity (CBD). 3. Research Assistant - Zoo Atlanta's African Biodiversity Conservation Program (1994 –1996). 127