Download Holocene vegetation change and the mammal faunas of South

Journal of Biogeography (J. Biogeogr.) (2004) 31, 943–957
ORIGINAL
ARTICLE
Holocene vegetation change and the
mammal faunas of South America
and Africa
Mario de Vivo* and Ana Paula Carmignotto
Museu de Zoologia, Universidade de São
Paulo, São Paulo, Brazil
ABSTRACT
Aim Although sharing many similarities in their vegetation types, South America
and Africa harbour very dissimilar recent mammal faunas, not only
taxonomically but also in terms of several faunistic patterns. However late
Pleistocene and mid-Holocene faunas, albeit taxonomically distinct, presented
many convergent attributes. Here we propose that the effects of the Holocene
climatic change on vegetation physiognomy has played a crucial role in shaping
the extant mammalian faunistic patterns.
Location South America and Africa from the late Pleistocene to the present.
Methods Data presented here have been compiled from many distinct sources,
including palaeontological and neontological mammalian studies, palaeoclimatology, palynology, and publications on vegetation ecology. Data on
Pleistocene, Holocene and extant mammal faunas of South America and Africa
allowed us to establish a number of similar and dissimilar faunistic patterns
between the two continents across time. We then considered what changes in
vegetation physiognomy would have occurred under the late Pleistocene last
glacial maximum (LGM) and the Holocene climatic optimum (HCO) climatic
regimes. We have ordained these proposed vegetation changes along rough
physiognomic seral stages according to assumptions based on current botanical
research. Finally, we have associated our hypothesized vegetation changes in
South America and Africa with mammalian faunistic patterns, establishing a
putative causal relationship between them.
Results The extant mammal faunas of South America and Africa differ widely in
taxonomical composition; the number of medium and large species they possess;
behavioural and ecological characteristics related to herbivore herding, migration
and predation; and biogeographical patterns. All such distinctions are mostly
related to the open formation faunas, and have been completely established
around the mid-Holocene. Considering that the mid-Holocene was a time of
greater humidity than the late Pleistocene, vegetation cover in South America and
Africa would have been dominated by forest or closed vegetation landscapes, at
least for most of their lower altitude tropical regions. We attribute the loss of
larger-sized mammal lineages in South America to the decrease of open
vegetation area, and their survival in Africa to the existence of vast savannas in
formerly steppic or desertic areas in subtropical Africa, north and south of the
equator. Alternative explanations, mostly dealing with the disappearance of South
American megamammals, are then reviewed and criticized.
*Correspondence: Mario de Vivo, Museu de
Zoologia, Universidade de São Paulo, Av.
Nazaré, 481 Ipiranga, São Paulo, SP 04263-000,
Brazil. E-mail: [email protected]
Main conclusions The reduction of open formation areas during the HCO in
South America and Africa explains most of the present distinct faunistic patterns
between the two continents. While South America would have lost most of its
open formations within the 30 latitudinal belt, Africa would have kept large areas
ª 2004 Blackwell Publishing Ltd www.blackwellpublishing.com/jbi
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M. de Vivo and A. P. Carmignotto
suitable to the open formation mammalian fauna in areas presently occupied by
desert and semi-arid vegetation. Thus, the same general climatic events that affected
South America in the late Pleistocene and Holocene also affected Africa, leading to
our present day faunistic dissimilarities by maintaining the African mammalian
communities almost unchanged while dramatically altering those of South America.
Keywords
Mammals, South America, Africa, vegetation change, HCO, LGM.
INTRODUCTION
South America and Africa share many landscape similarities,
including the presence of extensive rain forests, savannas,
steppes and deserts, but their contemporary mammalian
faunas are quite distinct (Keast, 1972; Vrba, 1993). Convergent
patterns such as would be expected as a result of faunistic
evolution over similarly structured landscapes (Bourlière,
1973) are actually not striking (McNaughton et al., 1993;
Cristoffer & Perez, 2003). The faunas differ widely in
taxonomical composition, they differ in the number of
medium and large species each continent possess; behavioural
and ecological characteristics related to herbivore herding,
migration and predation; and biogeographical patterns. However, this has not always been the case. Both faunas have
presented, at least from the Miocene onwards, convergent
characteristics, with diversified forest and open-formation
faunas, the latter inhabited by medium to large grazers and
browsers, all preyed upon by specialized carnivores (Cooke,
1972; Patterson & Pascual, 1972). In the Quaternary, this
scenario remained almost unaltered in Africa but changed
dramatically in South America, where open-formation mammal fauna lost practically all similarities to that of Africa.
Most authors believe that South America and Africa have
evolved their quite differently structured extant mammalian
faunas due entirely to distinct causes acting on each continent.
Considerable attention has been paid to the role of humans
(e.g. Martin, 1967, 1984), climatic change (e.g. Ochsenius,
1985; Cartelle, 1999) or the impact of North American
immigrant mammals on the ecosystems (e.g. May, 1978;
Marshall et al., 1982; Webb, 1985; Marshall & Cifelli, 1990). A
few faunistic comparisons have also appeared, but they have
been exclusively descriptive (Keast, 1972; Bourlière, 1973).
Vrba (1993) argued that global climatic events should be
employed in explaining faunistic patterns in South America
and Africa, however, she primarily described how climate
change affected the faunistic composition in South America as
a result of the Great American Interchange of the late Pliocene
and its after-effects during the Pleistocene. Additionally, all
previous attempts to study the faunas have assumed that the
late Pleistocene was the most significant period of change
(Martin & Klein, 1984; Ochsenius, 1985; Marshall & Cifelli,
1990; Webb & Rancy, 1996; Cartelle, 1999), but recent effort at
dating fossil mammals in South America revealed several
extinct species as living well into the middle Holocene (Faure
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et al., 1999; Baffa et al., 2000). Faure et al. (1999) dated a fossil
assemblage from north-eastern Brazil including the camelid
Palaeolama, the horse Equus and the giant armadillos,
Glyptodon and Hoplophorus, as c. 8490 and 6890 yr bp. Baffa
et al. (2000) dated a Toxodon from a karstic cave in southeastern Brazil to between 8000 and 5400 yr bp. This places
these large mammals well into the middle Holocene, and
considerably changes all previous views that the South
American megafauna would have been extinct by that time.
Besides, it indicates that analogously similar faunistic patterns
between South America and Africa have persisted beyond the
late Pleistocene.
Here we will demonstrate how the same late Pleistocene and
Holocene global events could have simultaneously affected the
faunas and disrupted the pattern of shared analogous similarities between South America and Africa. The impact of climate
change on vegetation at these times certainly affected floristic
composition. However, physiognomy change was probably
more significant for the mammalian faunas, with landscapes
alternatively showing denser and sparser facies through time.
Higher yearly average precipitation existing during the Holocene climatic optimum (HCO) would favour denser vegetation
physiognomies, thus reducing the availability of savanna-like
habitats for open formation faunas. However, lower averages
would open existing physiognomies and open formation
faunas would be benefited. Our continental level reconstruction of the vegetation changes in South America and Africa
provide a model that indicates why the same climatic events
led to a diversification of savanna mammal patterns in Africa
while practically extirpating them in South America.
IDENTIFYING FAUNISTIC PATTERNS
Past and present faunistic patterns
South America and Africa have always possessed taxonomically
distinct mammal communities throughout the Tertiary and
Quaternary (Patterson & Pascual, 1972; Maglio & Cooke, 1978;
Wilson & Reeder, 1993). This is significant in the sense that
any past or present similarities in ecological or behavioural
patterns are analogous, not homologous.
Throughout the Tertiary and Quaternary, South America
harboured 20 orders of mammals and Africa 13 (only terrestrial
forms; aquatic and volant mammals excluded). The recent fauna
is much less diverse for South America, with only 12 extant
Journal of Biogeography 31, 943–957, ª 2004 Blackwell Publishing Ltd
Vegetation change and mammal faunas in South America and Africa
orders and 11 in Africa (eight ordinal extinctions for South
America and only two for Africa). Considering the extant faunas
of the two continents, seven orders are shared, but have only two
genera in common, the carnivores Panthera and Mustela, which
are practically cosmopolitan taxa (Nowak, 1999).
Below is a summary of ecological, behavioural and biogeographical patterns that involve past and recent mammal
faunas in South America and Africa.
Diversification of continental faunas across weight categories
Figure 1 shows that Africa is richer in number of species for
any category above 5 kg; only in the weight category below
5 kg is South America richer than Africa (622 and 587 species,
respectively). There are no reliable weight estimates for extinct
mammals in both continents but Anderson (1984) furnishes
some adequate size estimates. If Pleistocene faunas could be
included in our graph, diversity within the weight categories
would have been quite similar between South America and
Africa. Most of the extinct South American medium and largesized mammals were associated with open formations
(MacFadden & Shockey, 1997; Cartelle, 1999; Rancy, 1999;
Cristoffer & Peres, 2003) therefore attracting attention to this
particular assemblage and its African counterpart.
Presence of grazer and mixed grazer-browser terrestrial
herbivores
Number of species
Among the largest African herbivores are the elephant, zebra,
rhinoceros, giraffe and hippopotamus, but the bulk of its
savanna diversity lies in the multitude of medium and largesized bovids (Bigalke, 1972; Peters, 1983). The extant South
American counterparts are the comparatively much less
impressive tapir, capybara, deer and the Andean camelids.
All South American herbivores are either mixed grazers and
browsers, or exclusive browsers, while Africa has a large
number of grazers (McNaughton & Georgiadis, 1986). As
–
–
–
–
Figure 1 Number of species per weight category; South America
in black and Africa in grey. Weight data from several sources,
mainly Nowak (1999). Africa presents more mammal species in all
categories above 5 kg, while South America is richer in the
category below 5 kg (see text).
Journal of Biogeography 31, 943–957, ª 2004 Blackwell Publishing Ltd
South America has extensive areas of open vegetation and did
possess a diversified grazer herbivore fauna (Patterson &
Pascual, 1972; Rancy, 1999; MacFadden, 2000), the loss of this
guild strongly affects any contemporary comparison. In fact,
bovids, which are responsible for much of the present day
distinctiveness of Africa, failed to enter South America at the
end of the Pliocene. This could lead us to think that their mere
absence would promote the faunistic distinction just described,
but South America did possess autochtonous herbivore orders,
such as Litopterna and Notoungulata which never extended
their distribution outside the Americas. Finally, even if all
bovids are excluded from the analysis, Africa would still
present an assemblage of large mammals for which no
equivalents can be found in modern South America.
Herding and migratorial behaviour
Group size among South American herbivores is usually small,
and solitary species are not infrequent, while Africa possesses
many herding herbivores, with groups ranging from dozens to
hundreds of individuals. These herds frequently migrate
seasonally in search of better pastures, while no herbivore
migration is known in the extant South American mammal
fauna except for small altitudinal shifts in the Andean camelids
(Kingdom, 1979; Nowak, 1999). The bulk of African mammal
species exhibiting herding and migratorial behaviours require
vast expanses of open vegetation to perform them
(Owen-Smith, 1988; Kappelman et al., 1997). The fossil record
shows that Plio-Pleistocene and present African mammal
faunas were similarly structured (Vrba, 1993; Kappelman
et al., 1997), but this is not clear for the Pleistocene mammals
of South America. Cartelle & Bohórquez (1982) believe that
the terrestrial sloth Eremotherium may have been gregarious,
while Webb (1999) envisages ‘vast herds of herbivores’ for the
continent. We suspect that South American gomphoteriid
mastodons may have lived in groups, as well as the horses
(Equus), as do phylogenetically close forms of today. The
Xenarthra is a monophyletic group and all extant xenarthrans
are solitary; the most parsimonious hypothesis is to suppose
that giant armadillos and terrestrial sloths would also have
been solitary, otherwise independent acquisitions of social
behaviour would have to be accepted. This is, of course,
possible, but less probable. Finally, we simply have no parallel
for how to characterize the herding behaviour of animals
belonging to extinct endemic orders of South American
mammals, such as the Litopterna and Notoungulata. These
animals could have formed ‘vast herds’, lived in small groups,
lived solitarily, or any combination of the former.
Specialized carnivore hunting and social behaviour: presence
of carrion eaters
All of the living South American predators hunt solitarily (with
the exception of canid Speothos venaticus, a small forest
dweller), while Africa has both solitary and group-organized
forms. Group organized hunters are mostly open vegetation
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M. de Vivo and A. P. Carmignotto
forms, like lions (Panthera leo), wild hunting dogs (Lycaon)
and hyenas (Hyaena, Crocuta). As prey size and availability are
factors that strongly influence the predation patterns of
carnivores (Vrba, 1980), group hunting has probably evolved
as a response to herd herbivory and the complex behaviours
involved can only be fully performed in open areas. South
America presented, for instance, sabre tooth felids adapted to
preying on large mammals and even specialized ‘giant’ vampire
bats, but these predators disappeared with their prey
(Simpson, 1980; Reig, 1981; Trajano & de Vivo, 1991). Finally,
Africa has a group of socially organized carnivores (hyenas)
that behave as opportunistic carrion eaters, which has no
extant mammalian equivalent in South America. For carrion to
be a major food source, it is probable that a large herbivore
biomass must be available.
presenting vicariant patterns for species and subspecies include
giraffes (Giraffa), dik-diks (Madoqua), kudus (Tragelaphus),
oryx (Oryx), antelopes of the genus Hippotragus, the lechwe
(Kobus), reedbucks (Redunca), gazelles (Gazella), African
buffalo (Syncerus), zebras (Equus), white rhinoceros (Ceratotherium), jackals (Canis), hyenas (Hyaena, Crocuta) and lions
(P. leo). The patterns just described probably emerged due to
the disappearance, in South America, of open vegetation large
mammals and their survival in Africa. The fossil record reveals
the presence of some vicariant species in South America
represented by Patagonian and Brazilian provinces species
(Cartelle, 1999). Nevertheless the fossil record is not accurate
enough to support or reject the presence of vicariant taxa along
the South American continent as a whole.
RESULTS AND DISCUSSION
Contemporary biogeographical patterns
Today, South America has two distinct mammalian faunistic
provinces, the Brazilian and the Patagonian (Hershkovitz,
1972). The Brazilian subregion actually extends from Central
America to Colombia, west of the Andes, and to the northern
half of Ecuador. To the east of the Andean cordillera, it
encompasses almost the entire tropical and subtropical South
America southwards to Bolivia and from there across Paraguay
to southern Brazil and adjacent Uruguay. The Patagonian
subregion includes the remaining parts of the continent: all of
South America west of the Andes from central Ecuador
southwards, and east of the Andes from south Bolivia to
Argentina and Uruguay. The Andes have no parallel in Africa
in continental extension and average altitude. Their presence
distorts the expected zonal distribution of alternating latitudinal humid and drier life zones due to their powerful
influence as a barrier to moisture carrying winds. To the west
of the Andes, dry and very dry climates prevail in tropical
latitudes even at sea level southwards from central Ecuador.
On the contrary, the expected zonal humid temperate climates
at latitudes around 60 appear only in Chile, and to the other
side of the Andes, the Argentinean Patagonia is steppic in
climate. The Patagonian province of South America includes
many genera and even families that do not occur in the
Brazilian subregion and vice versa. At least 27 genera of
rodents occur exclusively in the southern South America or at
the climatically equivalent high altitudes in the tropical Andes
(e.g. Lagostomus, Dolichotis, Abrocoma, Andalgalomys, Phyllotis, Graomys and Eligmodontia), the camelids Llama and
Vicugna, the cervids Pudu and Hippocamelus, the armadillos
Chaetophractus, Chlamyphorus and Zaedyus, the carnivore
Lyncodon, while entire families are tropical (the tree sloths
Bradypodidae and Megalonychidae; the Myrmecophagidae
anteaters; Cebidae and Atelidae primates; Echimyidae, Agoutidae and Dinomyidae histricognath rodents; Redford &
Eisenberg, 1992; Eisenberg & Redford, 1999). In Africa, the
most common pattern is the replacement of vicariant species
and subspecies along the north–south axis of open formations
(Haltenorth & Diller, 1977; Kingdom, 1977, 1979). Genera
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Commentaries on faunistic patterns
The patterns 1 to 4 described above are real: they underline the
distinctiveness of the extant South American and African
mammalian faunas. One question is if these patterns can in
fact be associated with the open formations. Another question
relates to the forest faunas: are they just as distinctive as the
open formation ones?
Our assumption is that large size, herding and migratory
behaviour, and social hunting techniques are strongly related to
open formations. This is not only intuitive, but also supported by
several lines of research (Clutton-Brock & Harvey, 1983; Peters,
1983; Owen-Smith, 1988; Kappelman et al., 1997). The terrestrial medium to large herbivores of the African rain forest are
either small-sized lineages (e.g. Cephalophinae bovids) or
dwarfed vicariants to savanna taxa. The duikers (Cephalophinae) represent a bovid lineage that is clearly forest adapted. Their
size is small (around 20 kg body mass), and they are either
solitary or live in small groups, up to three individuals
(Haltenorth & Diller, 1977; Peters, 1983). The forest buffalo
(Syncerus caffer nanus) is a distinct taxon than the savanna
forms, its body mass reaches a maximum of 300 kg, a weight
comparable with that of the South American tapirs. The two
savanna subspecies are much larger, reaching up to 800 kg body
mass. The differences in group size are remarkable: the forest
buffalo lives in groups of three to 12 individuals, while the
savanna’s taxa range from 20 to 2000 (Haltenorth & Diller,
1977). The forest elephant (Loxodonta cyclotis, a distinct species
according to Roca et al., 2001), is also quite smaller, with up to
half the weight and size of the savanna form. Average group sizes
are also quite distinct. The forest elephant averages 3.2 individuals per group, while savanna elephants average 10, but the latter
can form loose aggregations of up to 1000 individuals in the
rainy season (Haltenorth & Diller, 1977). It is revealing that
forest elephants actually use mostly forest clearings for much of
their activities; moving through the forest along paths to reach
alternative clearings (Vanleeuwe & Gautier-Hion, 1998).
The case of the forest buffalo and elephant is highly
significant because it indicates that elephants and buffalos
Journal of Biogeography 31, 943–957, ª 2004 Blackwell Publishing Ltd
Vegetation change and mammal faunas in South America and Africa
cannot be considered habitat generalists. The fact that forest
and savanna present vicariant taxa means that speciation, or at
least significant differentiation, has occurred. It is beyond the
scope of this article to discuss the history of speciation in the
African rain forests, but it is plausible that the large herbivores
presently living in African rain forests represent populations
once living in the open, that have been encircled by expanding
forest sometime in the past. These populations would have
become isolated from their savanna sisters and differentiated.
Analogously, it can be assumed that, while a fraction of the
large-sized savanna mammalian fauna of South America could
have vicariously inhabited South American rain forests, it
would still represent a minority of the taxa involved. However,
there is no evidence for the existence of such a large-sized
fauna in South American forests (Kay & Madden, 1997;
MacFadden & Shockey, 1997; Rancy, 1999; Cristoffer & Perez,
2003).
Cristoffer & Perez (2003) discuss the rain forest mammals of
South America and Africa, and indicate that forest lineages in
Africa have consistently evolved more terrestrial offshoots (in
the case of the African primate Cercopithecus). To this example
we could add the evolution of baboons (Papio) and our own
(Homo) (Reed, 1996). If African rain forests repeatedly
produced terrestrially adapted lineages, they are quite poor
in specialized arboreal locomotory adaptations. Prehensile
tails evolved independently at least six times in South
America: twice in Primates (Cebus and the ateline genera,
e.g. Brachyteles), rodents (Sphiggurus and Coendou), carnivores
(Potos), xenarthrans (Tamandua and Cyclopes) and marsupials
(all South American genera). In Africa, only pangolins (Manis)
possess prehensile tails. Emmons & Gentry (1983) showed that
African rain forests not only practically lack prehensile tailed
mammals, but also are very poor on gliding forms (only three
genera, Anomaluridae rodents), which abound in Southeastern
Asia. Emmons & Gentry (1983) attributed the evolution of
specialized locomotory adaptations in the world’s rain forests
to selective pressures derived from their differently structured
forest canopies and strata. It is not our aim to discuss the forest
patterns, but it is intriguing that South America has so many
independent acquisitions of prehensile tails, and Southeastern
Asia possesses several gliding vertebrates, while Africa shows a
remarkable poverty of both, and its forest lineages have
frequently evolved terrestrial offshoots.
Climate change and its influence on vegetation
Climate change has been evoked as playing an important role
in the megamammal Pleistocene extinctions (Graham &
Lundelius, 1984; Guilday, 1984; Ochsenius, 1985; Cartelle,
1999), but besides pointing out general consequences such as
drought, authors have refrained from building a model in
which tropical vegetation types would function under distinct
climatic regimes.
For the purpose of evaluating the impact of late Pleistocene
and Holocene climatic changes on the vegetation, we have
made the following assumptions.
Journal of Biogeography 31, 943–957, ª 2004 Blackwell Publishing Ltd
The geographical distribution of vegetation types
We have considered climatic changes affecting the present
geographical configuration of major vegetation types in South
America and Africa. There is a considerable body of research
on botanical palaeocommunities which reveals that floristic
composition has changed in the past 20 Ka (Coetzee, 1993;
Houérou, 1997; Colinvaux et al., 2000). Despite the growing
palynological knowledge, these reconstructions, however,
remain local and would render impossible any analysis that
considers South America and Africa simultaneously with all
their distinct biomes. Besides, we know very little about past
relationships between extinct mammal lineages and particular
floristic elements beyond the general inferences about grazing
and/or browsing habits. Thus, our focus is on physiognomic
changes of vegetation rather than floristic (see below).
How average precipitation levels affect vegetation
physiognomy
Our second assumption is generally applicable to tropical
landscapes, in that plant formations tend to present denser
concentrations of woody elements with greater water availability and vice versa (Fig. 2; Furley & Newey, 1983; Walter,
1984; Rizzini, 1997; Furley, 1999). The density of woody
species directly reflects on the amount of sunlight reaching the
soil and thus affects grass biomass.
One way to demonstrate that density of woody elements in a
vegetation varies with water availability through changing
precipitation levels is to examine the literature on areas
monitored for the effects of fire on vegetation. This is, of
course, an indirect approach as the climate (precipitation level)
has not actually changed in these areas. We assume that a
severe dry period lasting for a large number of consecutive
years, as would be the case at the beginning of a glacial period,
enhances the openness of a landscape through fires, either
natural or man made, while lesser deficits diminish the impact
of natural fire, as attested by several sources (Walter, 1984;
Miranda et al., 2002; Oliveira-Filho & Ratter, 2002).
In Africa, a number of studies have focused on the vegetation
changes due to the effects of seasonal fire and herbivory on the
vegetation. Salvatori et al. (2001) and Mapaure & Campbell
(2002) have shown that fire and herbivory play a significant
role in the decrease of woodland area and its transformation in
grasslands, but these authors have not been able to properly
distinguish between the independent contributions of fire and
herbivores. However, Dublin et al. (1990) showed that decrease
in woodland cover was due primarily to fire, large herbivores
playing a part mainly in the lack of regeneration of woodland
after its eradication by fire. Swaine et al. (1992) were able to
monitor controlled areas and demonstrated that trees become
more abundant if savannas are protected from fire. These
authors showed that in protected areas of savanna close to
forest vegetation, the regeneration included an expansion of
forest species, while in areas away from forests, the savanna
trees increased their density.
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M. de Vivo and A. P. Carmignotto
Evergreen forest
Semi-evergreen forest
Woodland
Tall Cerrado
Savanna
Dry forest
Mixed grass and shrub
Dry forest and shrub
Grassland
Steppe
Steppe
In South America, there are no large wild herbivores as in
Africa, but the net results are essentially the same. Studies on
the density of tree cover in the Venezuelan (San José & Farinãs,
1983, 1991) and Central Brazilian savannas (Moreira, 2000;
Hoffmann & Moreira, 2002) have shown that protection from
fire leads to denser physiognomies. McNaughton et al. (1993)
provide comparisons between vegetation structures of arid and
semi-arid regions of South America and Africa, concluding
that great general similarities can be observed, including the
response of open and dense savannas and woodland to fire.
Our model assumes that vegetation is much less vulnerable to
fire if precipitation levels are consistently higher, as would occur
during the prevalence of wetter climates and vice versa. The role
of soil in areas covered by savannas is, of course, essential, but
not as important in determining physiognomies than it is for
floristics. Following Oliveira-Filho & Ratter (2002), high fertility
unflooded soils will always sustain some kind of forest, from
semi-evergreen to dry. Low fertility unflooded soils will support
savanna vegetation, but if water availability is high and
seasonality not strongly marked, tall Cerrado (a kind of savanna
forest) and dense savanna occur; even semi-evergreen forests
can be found. Low fertility soils with strong water deficits will
sustain several kinds of open savanna.
The estimated effect of average water availability on
vegetation physiognomy is summarized in Fig. 2. This figure
presents two distinct paths of vegetation physiognomic change,
both commencing at levels of good water availability and
degrading to steppic or desertic conditions. The first series
ranges from rain forests and the second from dense arboreal
savanna. By keeping these two series separate we underline the
fact that savannas are soil dependent (Furley & Newey, 1983;
Sarmiento, 1984; Walter, 1984; Rizzini, 1997; Oliveira-Filho &
Ratter, 2002).
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Figure 2 Vegetation type physiognomies
under increasingly drier and/or more markedly seasonal climates (from top to bottom).
Elephants indicate those habitats suitable to
medium to large savanna mammals. We
believe that tall Cerrado, a kind of forested
savanna of Central Brazil and known as
‘Cerradão’ by South American botanists,
could not have supported large mammals
because it is denser and have less grasses than
typical African woodland.
How general were physiognomic changes in vegetation
Any vegetation map for South America and Africa is a
simplified view of how the floras and physiognomies are
spatially distributed. A vegetation such as the ‘Amazonian rain
forest’ actually encloses what we understand as ‘typical’ rain
forest and many other subtypes and enclaves. This makes our
assumptions (1) and (2) not immediately applicable at regional
or local scales, but adequate at continental level. Thus, when
we generalize the alteration of a vegetation physiognomy from
‘evergreen forest’ to ‘semi-evergreen forest’ or ‘dry forest’, we
are not stating that the entire biome has changed uniformly in
these directions, but only that the indicated resulting physiognomy would be the predominant one.
Our focus on the LGM and at the HCO makes distinctions
between the two periods straightforward: at the LGM the
prevalent climate over South America and Africa was drier,
while at the HCO it was wetter. We assume that the distinct
climatic regimes of the LGM and HCO prevailed over both
continents, acting over their entire range of different kinds of
vegetation cover.
The intensity and kind of the climatic change
We have considered a single variable in our model: the
precipitation levels. The rationale is the same as that we have
employed for the vegetation, i.e. we are aware that climate
change involves alteration in a vast number of variables, such
as temperature, aerial and marine circulation patterns, seasonality and others. However, not only are there no available
climatic reconstructions at such detailed level for South
America and Africa simultaneously, but also if such reconstructions were available, our data on the mammals would
Journal of Biogeography 31, 943–957, ª 2004 Blackwell Publishing Ltd
Vegetation change and mammal faunas in South America and Africa
certainly lag behind. We find that the best climatic variable
that can be reasonably studied with regard to its effect on
vegetation physiognomy is water availability, translated as
yearly average precipitation. As we cannot evaluate how much
the average precipitation would drop or increase, nor if
seasonal patterns would be maintained, we therefore have
assumed that under wetter and drier climates, all regions
would receive more or less rain by approximately the same
amount, thus affecting vegetation physiognomy in one direction. Finally, as we cannot know how much more or less
precipitation a continent received under a certain climatic
regime, we cannot ascertain whether a vegetation change
would be slight or else range across two or more of the
categories depicted in Fig. 2.
Below we briefly describe the present vegetation types of
both continents and the effect of climate change in the savanna
habitats and their mammalian faunas.
Present vegetation physiognomy in South America
and Africa
In South America the main areas covered today by evergreen
forest vegetation are the Amazonian rain forest (including, to
the west of the Andes, Colombia and northern Ecuador) and
the Atlantic rain forest of eastern Brazil (Fig. 3a). These forests
are mainly tropical, but a significant temperate rain forest
occurs in Chile, south of Valdivia. Between the Amazonian and
Atlantic tropical rain forests lies a vast strip of more or less
open vegetation types, extending across the continent. In
north-eastern Brazil is the Caatinga, a type classified as dry
forest and shrub (Eva et al., 2002). The central Brazilian
Cerrado is generally described as a savanna, but actually
includes savanna physiognomies and mesophytic forests as
well. In Bolivia, Paraguay and northern Argentina there is also
a dry forest and shrub, known as Chaco. An important area of
savannas occur in Colombia and Venezuela (the Llanos), and
two major enclaves of savannas can be found in northern
Brazil and adjacent Guyana (Gran Sabana). To the south,
Argentina has the extensive grasslands of the Pampas,
which gradually changes into steppe as we move south into
Patagonia. Just north of the Chilean temperate rain forest,
climates become ever more drier and the vegetation changes
accordingly: northwards from Valdivia, vegetation is gradually
altered into deciduous forest, shrub forest, steppe and desert
(Atacama). A large section of the Chaco is tropical to
temperate, and the Pampas and the Patagonian steppe are
entirely temperate. Thus, most of South America can be
described as consisting of three major areas of evergreen
forest – the Amazonian, the Atlantic, and the Chilean – with a
succession of more or less open vegetation types extending
from equatorial to temperate latitudes in between the first two
and northwards from the third (Hueck, 1966; Hueck & Seibert,
1981; Rizzini, 1997; Eva et al., 2002).
Africa presents a similar picture, albeit distinctively geographically organized (Fig. 3a). The main body of evergreen
forest is equatorial, occurring from the Atlantic coast to central
Journal of Biogeography 31, 943–957, ª 2004 Blackwell Publishing Ltd
parts of Africa, at the Albertine Rift, with an eastern arc
sweeping through Mozambique, Tanzania and southern
Kenya. Savanna, and savanna and forest mosaics surround
this forest. To the north, increasingly seasonal and drier
climates predominate, constituting a transitional region
between the savannas and the Sahara, known as the Sahel;
the vegetation becomes ever more open till the desertic
Saharan landscape. To the east and south of the equatorial
rain forests the same general pattern of open formations can
be verified, but more important areas of woodland and
mixed savanna and woodland can be found, from central
Angola to Tanzania and Mozambique. To the south of this
vast ‘woodland’ area, climate becomes drier and vegetation
changes accordingly into the xeric regions of the Namibian
desert and the Kalahari. Forests or forest mosaics appear in
the south-eastern coast of Africa, in Mozambique, mirroring
the South American Atlantic forest. In summary, most of the
African open formations lie surrounding evergreen forests,
within regions dominated by tropical and subtropical
climates. Africa does not possess sizeable land within
temperate domains, but the moderately high areas of the
Ethiopian and East African plateaus include altitudinal
vegetation gradients analogous to those found in parts of
the South American Andes (Cooke, 1972; Dickson, 1992;
McMaster, 1992; Carroll, 2001).
Vegetation physiognomies in South America
and Africa in the late Pleistocene and Holocene
Accepting the assumptions described above, we may discuss
what changes would occur over the continents in terms of their
vegetation cover. Considering that, world-wide, the LGM of
the late Pleistocene was drier than the present (Flenley, 1979;
Whitmore & Prance, 1987; Clapperton, 1993; Colinvaux et al.,
2000; Whitlock et al., 2001), we associate our maximum
vegetational openness scenario with this phase.
Figure 3b shows our reconstruction of vegetation physiognomies for both continents during the LGM. As can be seen,
subjected to lower precipitation averages, evergreen forests
would degrade to semi-evergreen and could as well present
more open patches of savanna-like physiognomies in a mosaic
pattern. This kind of change would occur along vast areas of
rain forest if precipitation dropped significantly. That this kind
of change took place in South America can be verified by the
fact that the Amazonia is mainly covered by rain forest, but
include hundreds of isolated patches of savanna (Hueck &
Seibert, 1981). Areas covered by semi-evergreen forests, dry
forests, woodlands and savannas would generally open up as
well. Forest would be mostly restricted to mountain ranges
subjected to orographic rain and to other areas where rainfall
would still be high enough. The retracting forests would leave
space for drier seral stages in the forest succession (as seen in
Fig. 2), and in areas with poor soils, savannas could be
established. Vegetation types that are presently subjected to
semi-arid and arid climates, such as deserts, South American
grasslands, steppes and the south African areas of mixed grass
949
M. de Vivo and A. P. Carmignotto
and shrub would become even drier. Mountain ranges would
be affected somewhat differently, in that altitude and not only
latitude would play a part. Altitudinal zonation would
probably be found at correspondingly lower altitudes than
those found today.
As we enter the Holocene, climatic conditions changed.
Figure 3c shows our reconstruction of the prevailing vegetation
physiognomies in South America and Africa at the HCO. For
Africa, there is a well-established pattern of ever more humid
climate reaching the hypsithermal interval, or the HCO at the
middle Holocene, followed by a return to drier conditions in
the present (Coetzee, 1993; Houérou, 1997). During the HCO,
African rain forests would be under ideal humidity conditions,
probably expanding to tropical areas where soil could support
it. Open woodlands would likewise present denser vegetation.
Thus, open formations would be eliminated in certain areas or
reduced in others, but would actually expand into regions
previously too dry to support it, such as desertic areas. For
South America, the HCO is less consensual. Some authors
(Bradbury et al., 1981; Bigarella & de Andrade-Lima, 1982;
Hare, 1992; Joly et al., 1999; de Oliveira et al., 1999) propose
the same pattern as that just described for Africa, that is, the
HCO occurring from early to middle Holocene. However,
palynological studies throughout the continent resulted in
somewhat conflicting results in the sense that some regions
would have received more rainfall with others experiencing
desiccation at the same moment, even within the tropics
(Ledru et al., 1998; Salgado-Labouriau et al., 1998; Behling &
Hooghiemstra, 2001). The same can be said of researches
relying on different or broader data bases (Clapperton, 1993;
Colinvaux et al., 2000). Generally, they sustain that most of the
Holocene was drier than the present, gradually becoming ever
more humid in the last 5000 years, approximately – although
not uniformly – over the entire tropical South America.
Irrespective of a middle or late Holocene HCO for South
America, both Amazonian and Atlantic rain forests would be
under their best climatic conditions, while dry forests such as
those of Caatinga and Chaco would turn into semi-evergreen
forests. Tropical savannas could maintain their floristic
identity but its woody component would have become densely
packed, with marked reduction of grassland areas. Grasslands
and wetlands within tropical South America could probably
still be found, but predominant physiognomies would be dense
savanna and tall, forest savannas.
Figure 3d presents a summary of our model, showing that
areas within and without the 30 latitudinal belt would present
complementary and opposite characteristics during the LGM
and the HCO. A major distinction between South America and
Africa is established in that, during the HCO, the latter
continent would maintain large expanses of suitable habitats
for medium- and large-sized open vegetation mammals, both
to the north and to the south (the Sahara and the southern
xeric regions of Namibia and the Kalahari), whereas South
America would present its physiognomically suitable areas
only at the colder, temperate lower latitudes of the southern
part of the continent.
950
Mammal faunas and vegetation change
Changing climate effects on vegetation and mammal faunas is
a well-documented feature of the evolutionary history of
mammals. The Miocene, with its world-wide expansion of
grassland habitats is associated with the radiation of several
herbivore lineages both in South America and Africa; at the
end of the Miocene, when grasslands retreated, extinction
of part of these lineages followed suit, at least in South
America (Patterson & Pascual, 1972; Janis, 1993; Vrba, 1993;
MacFadden, 2000). We would expect the same pattern
occurring during the Pleistocene–Holocene climatic and
vegetation change of the magnitude proposed here. In
addition, we should expect the entire mammal fauna to be
affected, not only its larger-sized lineages. Roughly, faunistic
assemblages adapted to open vegetation environments should
either become extinct or isolated within pockets if this
vegetation is replaced by forest, and when open landscapes
replace forests, the same would happen with the forest-adapted
taxa. This is indeed the case, as we demonstrate below.
Pardinãs et al. (2002) summarized several dramatic changes
in the composition of small mammal communities in southern
South America from the late Miocene to the Holocene. The
ecological implications of these changes in the taxonomic
structure of the communities is not entirely understood, but
these authors attributed most of the small mammal distributional changes to climate and its effect on vegetation. Evidence
that the Amazonian rain forest was widely penetrated by open
formations is provided by some studies on the distribution of
small mammals with pronounced habitat fidelity. The marsupial Lutreolina occurs from the Buenos Aires province in
Argentina northwards until the Brazilian States of São Paulo,
Goiás and Mato Grosso do Sul, always being associated with
open vegetation habitats. Its distribution is then interrupted by
the Amazonian rain forest, and the same species reappear in
the open areas of Venezuela and Colombia (Nowak, 1999).
Nunes (2001) studied small mammal communities within
several isolated savanna enclaves within the Amazon basin and
found that some of its rodents represented disjunct populations from species inhabiting the northern and central South
American savannas, which implies that these rodents had a
wider distribution in open habitats and survived in savanna
pockets when the forests returned. We have already mentioned
above that the presence of vicariant species such as the forest
elephant (L. cyclotis) and the forest buffalo (S. caffer nanus)
within the African rain forest may represent the same
phenomenon of forest retraction followed by expansion and
‘capture’ of open enclaves for that continent, although the
dates involved may be different. In the case of the South
American small mammals, most of the species did not speciate,
indicating that the disjunction events may be quite recent.
The study of extinct Amazonian mammals reinforces the
same scenario. Webb & Rancy (1996) and Rancy (1999)
describe in detail the Amazonian Pleistocene open formation
mammal fauna and concluded that there was a need for
savanna habitats to sustain them. However, Colinvaux et al.
Journal of Biogeography 31, 943–957, ª 2004 Blackwell Publishing Ltd
Vegetation change and mammal faunas in South America and Africa
30 N
(a)
Desert
Desert
Woodland
Savanna
Savanna
(b)
Open savannas
Open savannas
Equator
Evergreen forest
Evergreen forest
Dry forest
Mosaic of open forests
and savannas
Mosaic of open forests
and savannas
Woodland
Savanna
Desert
Open savannas
Semi evergreen
and evergreen
forest
Mixed grass and shrub
Grassland
Dry forest
30 S
Evergreen
forest
Grassland / Steppe
Desert
Grassland / Steppe
Desert / Cold Steppe
(c)
Savanna
Suitable during HCO
Unsuitable during LGM
Dense savanna
(d)
Suitable during LGM
Unsuitable during HCO
Dense savanna
Evergreen forest
Evergreen forest
Dense savanna
Suitable during LGM
Unsuitable during HCO
Evergreen and
semi evergreen
forests
Evergreen and
semi evergreen forests
Evergreen
forest
Savanna
Temperate formations
Suitable during HCO
Unsuitable during LGM
Suitable during HCO
Unsuitable during LGM
Figure 3 Present day major plant formations of South America and Africa (a) and geographical vegetation change for the two continents at
the LGM (b) and the HCO (c). A summary of this change is depicted in (d), where darker grey are for areas of predominantly suitable
megafauna habitat at the LGM and unsuitable habitats at the HCO; and lighter grey are for areas predominantly suitable habitats at the HCO
and unsuitable at the LGM. White areas in the maps of South America mostly indicate complex Andean vegetation not considered here.
(2000), working on western Amazonia Pleistocene palynological record, sustained that most of the Amazon lowlands
remained as a forest throughout glacial cycles; proposing that
these extinct mammals actually lived in forests, and that all
extinct grazers would be restricted to river margins, where
grasses could be found. We agree with most authors (Webb &
Rancy, 1996; Rancy, 1999; Cristoffer & Perez, 2003) in that
Amazonian forest as it is today could not support the
megafauna. In our view the question of physiognomy vs.
floristics is crucial here. Arboreal or grass pollen do not furnish
an immediate picture of how densely or sparsely forested a
region would be; instead they reveal floristic assemblages. Thus,
for instance, arboreal pollen might be recovered from a site
sustaining a woodland or dry forest (see Pennington et al.,
2000), which is rather more open and more suitable to the
Journal of Biogeography 31, 943–957, ª 2004 Blackwell Publishing Ltd
megafauna than a rain forest. Spatial organization of plants is
not immediately revealed by pollen lacustrine deposits, it is
only suggsted by it, as structural reconstruction depends on the
knowledge of our present-day floristic communities.
If the HCO resulted in the spread of closed, forest
environments over previously open landscapes, we should
expect that forest-adapted mammals would leave signals of
their presence in areas presently covered by open formations.
Voss & Myers (1991), Emmons & Vucetich (1998) and Silva
et al. (2003) documented that several species of small sigmodontine and histricognath rodents that are otherwise still
living in forest areas elsewhere have been found as ‘Pleistocene’
fossils in the central Brazilian site of Lagoa Santa, in the State
of Minas Gerais. This locality is today covered by savanna
vegetation, and most of the rodents listed by those authors are
951
M. de Vivo and A. P. Carmignotto
forest dwellers. Their disappearance from a savanna locality
and survival in forests elsewhere indicates that ecological
changes in vegetation distribution were probably responsible
for their local extinction. Cartelle & Hartwig (1996) described
two Pleistocene extinct folivorous monkeys from a fossil site
within the present-day Caatinga (dry forest and shrub). This
kind of vegetation cannot support highly herbivorous
monkeys, and thus they must have inhabited considerably
moister forests. de Vivo (1997) showed several cases of
disjunction between species of arboreal mammals occurring
in eastern Amazonian rain forest and north-eastern Brazilian
Atlantic rain forest. Between these two rain forests, there is the
Caatinga, which cannot presently support these species. These
disjunctions appear to be quite recent because no differentiation can be detected for the populations involved.
In Africa, there is evidence for the expansion of savanna
mammal communities to areas covered today by desert.
Savanna invaded what is today the Saharan desert at the
Holocene HCO, as is beautifully attested by the rock art left by
humans from 8000 to 1000 yr bp. Wild savanna mammals,
such as giraffe, hippopotamus, elephant and several bovids
were depicted in hunting scenes, and gradually were replaced
in the paintings by cattle. Finally, at the end of the HCO even
cattle are no longer depicted and the Sahara took its present
arid configuration (Camps, 1974; Scarre, 1988; Houérou,
1997).
Thus, there is considerable evidence that open and forestadapted mammal faunas have changed their distribution
patterns in the past few thousand years, probably as a result
of change in the vegetation physiognomy. If these vegetation
changes have occurred as depicted in Fig. 3, the large-sized
South American mammal lineages, mostly adapted to open
formations, would have found reduced adequate landscapes in
tropical and subtropical regions during the HCO, with its
massive forest expansion. Most populations would become
extinct and the few isolated ones would be much more
vulnerable to accidental extinction or to human predation. In
Africa, the savanna-adapted mammals would still find vast
expanses of suitable habitats both in the subtropical north and
south parts of the continent, and the populations would be
under much less stress.
As glacial and interglacial cycles occurred throughout the
Quaternary, some of the faunistic patterns may have been
established earlier. However, there is evidence that the last
glacial and interglacial cycle was particularly intense and
abrupt relative to previous cycles, at least relative to the last
100 Ka (Hambrey & Harland, 1981; Haffer, 1982; Bartlein &
Prentice, 1989; Roy et al., 1996). All Quaternary glaciation
cycles supposedly had the same general effect on vegetation,
albeit with varying intensity. Thus, we think that most of the
previous Pleistocene extinctions could be attributed to the
alternating glacial and interglacial cycles, but the final coup
would have been administered by the last one.
It remains to be explained why the southern cone of South
America, which was subjected to colder and drier conditions at
the LGM, would not have supported most of the savanna
952
mammals at the Holocene HCO. The mammalian fossil record
tells some of the story. Cartelle (1999) compiled data from
several independent researchers of fossil Argentine mammals
of the late Pleistocene (LGM) which show that this temperate
fauna migrated to northern, more tropical localities at this
period, separated by severe cold and steppic environments.
(see also Ficcarelli et al., 1997; Coltorti et al., 1998; Núñez
et al., 2001). During the HCO, expanding savannas could have
become available again only in the temperate southern cone of
South America. Animals adapted to tropical conditions would
find it a harsh environment and thus only a fraction of the late
Pleistocene tropical savanna fauna would have returned. Our
hypothesis thus predicts that any Holocene assemblage of
mammals from the temperate southern cone will be poorer
than contemporary tropical ones. Most of the present day
dissimilarities between Africa and South America would then
be established at the Holocene.
A critique of previous hypotheses on the extinction
of the South American megafauna
Alternative hypotheses have been proposed, namely (1) the
action of human hunters entering the American continent and
overexploiting the fauna (Martin, 1967, 1984); (2) the
elimination of phyletic lineages due to a faunistic imbalance
caused by the invasion of North American mammals in South
America after the Great American Interchange of the late
Pliocene (May, 1978; Marshall et al., 1982; Webb, 1985); and
(3) the intense dry phase of the late Pleistocene (Ochsenius,
1985; Cartelle, 1999).
Martin (1967, 1984) proposed that humans entering the
Americas some 12 000 years ago overhunted a ‘naive’ mammal
fauna that, having never faced such resourceful predators,
provided easy and abundant meat. We reject it for several
reasons discussed below.
Martin (1984) proposed two possible features that would be
discordant to his model: (1) the extinction of small mammals
(not vulnerable to human impact) and (2) the extinction of
large mammals before prehistoric human arrival. Both phenomena have been recorded for South America.
The extinction of small forest mammals in areas presently
covered by savannas has already been explored in the previous
section. Ficcarelli et al. (1997) and Coltorti et al. (1998)
described and dated sites in the Andes of Ecuador and in the
northern Peruvian coast where mastodons and giant sloths
became locally extinct before the arrival of man at the end of
the Pleistocene (between 16 670 and 12 350 yr bp), while for
areas in the Equatorial Andes more subjected to cold climates,
the extirpation of the megafauna dated from c. 20 980 yr bp.
Ficcarelli et al. (1997) cite other similar cases for the Argentine
plains. Núñez et al. (2001) also describe and date a site in
northern Chile where the arrival of humans found the
megafauna already gone, and archaeological sites reveal
remains of extant mammals (late Pleistocene, c. 10 800 yr
bp). Ficcarelli et al. (1997), Coltorti et al. (1998) and Núñez
et al. (2001) attributed the disappearance of large mammals
Journal of Biogeography 31, 943–957, ª 2004 Blackwell Publishing Ltd
Vegetation change and mammal faunas in South America and Africa
from these sites to climatic change (excessive cold and dryness
at the end of the Pleistocene).
Additionally, Martin (1984, p. 360) argues that if the
disappearance of large mammals through human agency was
‘truly swift and devastating’, few kill sites would have been
found. Indeed, no kill sites have been found in South America,
and the extended presence of large mammals in the midHolocene (described above) suggests that the absence of such
sites is not favourable to Martin’s scenario. There are a few
archaeological sites where evidence of some large mammals
hunted by humans have been found (Taima-Taima, Venezuela,
Gruhn & Bryan, 1984; southern Patagonia, Markgraf, 1985;
north-eastern Brazil, Guérin et al., 1996; Tagua-Tagua and
Monteverde, Chile, Núñez et al., 2001). The analysis of these
publications clearly indicates that humans did hunt large
mammals in South America, but the sites can hardly be
described as ‘kill and processing sites’. The dating of midHolocene large mammals in South America (summarized
earlier) far extends the presence of these animals in the
continent simultaneously with the presence of humans,
contradicting an extremely rapid rate of megamammal extirpation through excessive hunting. We believe that human
predation of large South American mammals did occur, but
that it may have played a marginal role, probably in the
elimination of small isolated populations.
Beck (1996) disagrees with Martin’s blitzkrieg hypothesis for
North America, based on the geographical and temporal
distribution of the megafaunal remains which do not fit the
direction and timing of human migration from north-west to
south-east North America, as should have happened under
Martin’s assumptions. Beck (1996) emphasizes that his data
does not preclude the possibility that changes in climate were a
more important factor.
Martin (1984) argues that the long coevolutionary history of
humans and the megafauna in Africa and southern Asia would
account for the survival of the animals in those regions. The
animals would have learned to recognize humans as threatening and developed avoidance behaviours. As large mammals
were present in the South American Holocene, the ‘overkill’
period would have to be extended from at least 12 000 to
c. 6000 yr bp (some authors claim earlier dates for human
entry in the American continent; see Rudgley, 1999). With
such long period of co-habitation, South America would not
have any ‘naive’ mammals left; they would all have learned to
recognize and avoid humans, which is exactly what large
mammals in Africa and Asia did.
A second hypothesis dealing with (but not only) the South
American mammal extinctions at the end of the Pleistocene is
related to predictions contained in the Equilibrium Theory
(MacArthur & Wilson, 1967), in which land masses are
believed to reach relatively stable numbers of lineages given
enough time. May (1978), Marshall et al. (1982), Webb (1985)
and Marshall & Cifelli (1990), applying the Equilibrium
Theory to the palaeontological history of New World mammal
faunas, generally considered it as a viable alternative explanation for the South American extinctions. To them, the number
Journal of Biogeography 31, 943–957, ª 2004 Blackwell Publishing Ltd
of taxa that resulted from the sum of North American invaders
plus the southern native mammals far exceeded the carrying
capacity of the South American continent after the Great
American Interchange at the end of the Pliocene. We reject this
hypothesis. If the Equilibrium Theory explains the South
American extinctions, we should expect a decrease in the
number of lineages after the Great American Interchange, and
that indeed occurred. However, it is not at all clear why these
extinctions were concentrated on larger mammals, as demonstrated by Lessa et al. (1997). If an excessive number of
lineages is the factor behind extinctions, we should expect that
small, medium and large mammals would have been equally
affected, but that is not what happened as we associate larger
body sizes to the habitat preferences of the mammals (as
discussed above, larger mammals tending to live in open
formations), we believe that our hypothesis furnishes a better
explanation for the known facts.
Ochsenius (1985) and Cartelle (1999) proposed that the
South American megafauna extinctions occurred in the late
Pleistocene due to climatic change, relating it to the cold and
dry conditions of the LGM. We agree with both authors that
this indeed occurred, at least locally (Ficcarelli et al., 1997;
Coltorti et al., 1998; Núñez et al., 2001). Our hypothesis,
however, considers the presence in the mid-Holocene of some
lineages of large mammals, which was ignored by both authors.
The LGM climatic conditions cannot be assumed as the sole
explanation for the extinctions, and a new perspective must be
considered. The Holocene and its climatic events should be
taken into account.
CONCLUDING REMARKS
All characteristics related to the special savanna attributes of
herbivores and predators are largely dependent on the existence
of vast extensions of open spaces with abundant grasses. In
South America these spaces were severely reduced in tropical
and subtropical areas during the HCO. The present savannas of
Africa were probably affected in the same manner, but then
Africa had ‘escape’ areas in its deserts, north and south. These
deserts, under a more humid climate, would present savannalike physiognomies, thus sustaining entire savanna communities. The same climatic events could additionally explain the
contemporary existence of vicariant patterns in the African
savanna vs. distinct faunistic assemblages in the South
American open formations (tropical and temperate). In Africa,
the savannas invading former desertic regions, plus savanna
isolates inside the tropical areas of the continent, could sustain
isolated savanna mammal communities, which suffered differentiation resulting in the current vicariant pattern. Evidently,
this could have occurred before, during the several glacial and
interglacial cycles of the Quaternary, not only in the last one,
thus reinforcing differentiation. However, South America
would have lost most of its tropical and subtropical savannas.
Grasslands in temperate South America, already somewhat
depopulated in the late Pleistocene (see above), did not recover.
What remained in the tropical and subtropical vs. the
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M. de Vivo and A. P. Carmignotto
temperate areas of the continent were the distinct faunistic
complements found today.
In conclusion, we believe that South America and Africa did
share similar faunistic patterns until quite recently (middle
Holocene) and that vegetation changes associated with fluctuating rainfall levels physiognomically altered habitats available
for the open formation fauna. Present-day faunistic differences
between these continents would arise not because the events
affecting them were different, but because open formations
survived in far greater extensions in Africa than in South
America during the more humid phases of the Holocene.
ACKNOWLEDGMENTS
Erika Hingst-Zaher, Mario de Pinna, Eliana Marques Cancello,
Alexandre Reis Percequillo, Daniel Jelin and two anonymous
referees read earlier versions of this manuscript and offered
valuable criticism and suggestions. This research was supported by FAPESP (grants 98/05075-7 and 00/06642-4).
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BIOSKETCHES
Mario de Vivo is Chair of Vertebrates and Curator of
Mammals and Birds at the Museu de Zoologia, Universidade
de São Paulo. His main research interests are the systematics of
South American mammals and their biogeography.
Ana Paula Carmignotto is in the PhD Program of Zoology
at the Instituto de Biociências, Universidade de São Paulo,
currently developing her thesis research at the Museu de
Zoologia, USP. Her interests are ecology and biogeography of
open formation small mammals.
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