Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Chapter 43: Living in communities Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University 43-1 Species coexist and interact in communities • Ecological views of coexisting species range from coevolved, highly interactive communities to loose assemblages of species • Community ecology focuses on: – community structure, i.e. the relative abundance of component species – species dynamics (changing abundance) in space and time – species interactions Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University 43-2 Species diversity • Simplest measure is the number of species present—this is species richness • Better to include a measure of relative abundance, called alpha (α-) diversity • Beta (β-) diversity measures the diversity between communities separated in space • When comparing diversity, the area sampled (or time spent sampling) for all communities must be standardised Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University 43-3 Measuring diversity • Simpson’s index (below) is one of several different diversity indices n D 1 i i 1 N s 2 where ni is number of individuals in species i, N is total no. of individuals in the community and S is the no. of species present. • D ranges from 0 to 1, and is affected by the total number of species as well as their relative abundance Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University 43-4 Structural diversity of plant communities • Describes variations in size and shape irrespective of species • Provides information on biomass and productivity • Uses two components – projective foliage cover = % of ground above which there is foliage – height of foliage • R. L. Specht’s structural classification has been widely used in mapping Australian vegetation Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University 43-5 Fig. 43.4: Plant communities Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University 43-6 Interactions within communities: symbiosis • Symbiosis occurs when two organisms live closely together and at least one benefits e.g. coral polyps and symbiotic algae • Partners may have coevolved, e.g. orchid flower mimics female wasp • Symbiosis is common in complex communities • There are three kinds of symbiotic interactions – commensalism – mutualism – parasitism Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University 43-7 Commensalism • One species benefits, the other is unaffected • Examples – Moist forest: epiphytes on tree trunks – Marine rocky shores: ‘decorator’ crabs and molluscs with attached algae • Over time, the relationship may change, e.g. a strangler fig is a harmless epiphyte when small, but grows into an aggressive competitor Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University 43-8 Mutualism • Both partners benefit • Examples – lichen (an alga and a fungus) – mycorrhiza (a fungus and the root of a higher plant) – symbiotic algae in tissues of coral animals and giant clams – sea-anemone and anemone fish – ant colonies in domatia provided by plants • Advantages may include food, protection, removal of wastes, provision of living space Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University 43-9 Fig. 43.7: Anemone fish and its symbiotic partner, the anemone Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University 43-10 Parasitism • One partner benefits, the other is harmed but not usually killed • Parasites typically smaller than host • Ectoparasites live on surface of host, e.g. lampreys • Endoparasites live internally, e.g. tapeworms • Parasitoids are insects that are parasitic only in their larval stage • Parasitism is a special kind of predation Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University 43-11 Fig. 43.9: Parasitoid Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University 43-12 Question 1: Which of the following statements is true? a) Symbiosis refers to different organisms living together. b) Members of a symbiotic relationship cannot live without each other. c) Symbiosis refers to different organisms living together and benefiting from each other. d) A parasite is not in a symbiosis with its host. Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University 43-13 Predation • One organism feeding on another • Numbers of predators and prey may show oscillations called predator–prey cycles, but these are rarely simple because: – unpredictable fluctuations in environment occur – predator is likely to eat more than one prey species – prey species is affected by the quality of its own food Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University 43-14 Fig. 43.12: Seasonal changes in the number of insects on the grass Holcus mollis in relation to changes in food quality, measured as nitrogen in leaves and stems Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University 43-15 Fruit eaters aid seed dispersal • Frugivores are herbivores that specialise as fruit eaters • In Queensland rainforests 84% of plants were found to produce fleshy fruits (CSIRO data) • Frugivorous birds digest only the fruit • Fruit pigeons and cassowaries have thin-walled gizzards that do not grind up the seed • Seeds are dispersed and voided to forest floor (with a small dose of fertiliser!) • This is an example of an ecosystem service (see Ch 44) Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University 43-16 Predation and biological control • Works best where the predator – is monophagous (feeds on single prey type) – drives prey to very low numbers – survives in low numbers itself • Successful Opuntia (prickly pear cactus) has been controlled by Cactoblastis moth larvae • Unsuccessful Cane beetle Dermolepida was unaffected by the cane toad Bufo marinus, which has now become a major pest species Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University 43-17 Plant defences • Natural selection has resulted in the evolution of plant defence mechanisms against being eaten – – – – tough leaves spines hairs chemical deterrents (e.g. tannins and toxic alkaloids) • Many animals have evolved ways to cope with plant toxins – eat a small amount of a wide variety of plants – contain detoxifying enzymes (e.g. Colobine monkeys) – tolerate poisons (e.g. kangaroo and fluoroacetate in pea family) Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University 43-18 Animal defences • These include speed, agility, size, camouflage, toxic chemicals, physical barriers and behavioural adaptations • Animal may accumulate toxic compounds from its food to make it unpalatable e.g. Monarch butterfly • Harmless insects may mimic toxic models. This is Batesian mimicry (successful provided there are more models than mimics) Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University 43-19 Keystone predators • Presence or absence of keystone predator has a major effect on community structure • Sea star Pisaster ochraceus controls diversity of rocky shore community by controlling mussel abundance – removal of Pisaster mussels out-compete other species for space – in presence of Pisaster, weaker competitors survive because mussels are controlled • There are not many good examples of truly keystone species Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University 43-20 Competition • Only occurs when a resource is in short supply e.g. food, light, shade, space, moisture • Can be within a species: intraspecific competition • Or between species: interspecific competition Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University 43-21 Types of competitive interaction • If a resource is used up exploitative competition – nutrients exhausted; e.g. ants remove seeds from an area • Prevention of access to resources interference competition – resource not consumed; e.g. tall trees shading neighbours Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University 43-22 Ecological niche • Defined by all the biotic and abiotic factors that affect survival of a species • A species uses only the realised niche (a part of the multidimensional and bigger fundamental niche) • Niche breadth is the range of a resource that the species uses Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University 43-23 Fig. 43.22: Idealised niche space Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University 43-24 Niche overlap and character displacement • Organisms compete if their realised niches overlap in time or space • Resource partitioning is a mechanism that minimises niche sharing, e.g. forest birds feeding at different heights above ground • Morphological changes that assist in resource partitioning are promoted by natural selection, e.g. bill size in seed-eating birds • Natural selection acts on individuals, and evolution acts on the population, to promote character displacement in sympatric populations Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University 43-25 Communities are not constant: succession • Succession is a theory about how communities change • Each stage is called a sere • Earliest sere consists of disturbance opportunists – Small, multiply quickly, short-lived – ‘r’ strategists • Stable sere is the climax community – Larger, slower growing, best long-term competitors – ‘K’ strategists Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University 43-26 Disturbance affects many communities • Disturbance may result from fire, grazing, predation, pollution, trampling, flood, exotic pests etc. • Fire and other disturbances can promote diversity • Intermediate disturbance hypothesis (Connell, 1977 and others): frequency of disturbance is important • Mosaic of patches of different ages enhances diversity Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University 43-27 Humans can act as novel disturbances • Vegetation clearing, uncontrolled burning, dredging seabed, trampling rocky shores • Temporal and spatial scale of human activities may be unlike natural processes, e.g. fire as tool for hunting • Combined effects of natural and man-made disturbance exert new selective pressures and competitive interactions Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University 43-28 Communities are the result of many different interactions • Competition, predation and disturbance all vary and interact • Community structure can be determined by – bottom-up (nutrient) controls – top-down (competition, predation) controls – recruitment and immigration • Manipulative ecological experiments are a powerful tool to unravel these processes • Rocky shore community structure results from a combination of biotic processes modified by physical environment and random disturbances Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University 43-29 Biomes: communities on a global scale • Biomes are ecological communities delineated by climate • Biomes result from evolutionary convergence • A biome may comprise several plant communities, e.g. alpine biome includes herb-fields, heaths, fens and bogs Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University 43-30 Fig. B43.4a: Major world biomes Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University 43-31 Gradients and ecotones • Community boundaries are called ecotones • Ecotones may be species-rich because they include individuals from adjacent community types • Species are replaced along gradients, resulting in patterns of zonation, e.g. mangrove trees Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University 43-32 Fig. 43.34a: Mangroves (Rhizophora stylosa) Copyright © marinethemes.com/Kelvin Aitken Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University 43-33 Fig. 43.34b and c: Distribution of three mangrove species Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University 43-34 Summary • Community structure can be summarised by measures of diversity • Species interact in many different ways. This can include symbiosis, predation and competition • Mutualism, commensalism and parasitism are all forms of symbiosis • Competition between different species for a limited resource is interspecific competition • Disturbance of a community may reduce the frequency of competition and aid in maintaining diversity Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and Saint Slides prepared by Karen Burke da Silva, Flinders University 43-35