Wednesday, 5 December 2012

The African Anomaly

Africa is the ‘anomaly’ in the Pleistocene megafauna extinction debate because it only lost 21% of its megafauna species, in contrast to the high levels of extinction in other continents. Today, it also contains a much higher level of megafauna diversity than other continents, including some species which have survived from Pleistocene times, such as the Cape Buffalo. 

Climate Change, Refugia and Disease

Climate change in Africa has been associated with dramatic species extinctions in the whole Pleistocene, not only the late Pleistocene. 59% of the Pleistocene megafauna extinctions occurred in the early Pleistocene, 21% in the middle Pleistocene and 20% in the late Pleistocene. All of the late Pleistocene extinctions happened during the late Pleistocene/Holocene transition (Graham and Lundelius 1984). 

The present-day megafauna has been called a ‘living Pleistocene fauna’ (Graham and Lundelius 1984: 240) because of their diversity is almost similar to the diversity of the extinct Pleistocene megafauna. Graham and Lundelius (1984) argue that perhaps the rate and magnitude of climate change was slower in Africa than in other continents, thus explaining the lower rates of megafauna extinction. Savannah environments survived into the Holocene in Africa while they disappeared in other parts of the world. For example in South America, savannah environments were abundant during the late Pleistocene but is today restricted to only a few areas. Other explanations for the African Anomaly have been put forward, although many of these tend to be speculative as Africa is the least studied continent with regards to late Pleistocene megafauna extinction. One possibility is that Africa has a great variety of habitat types which may offer better refugia for megafauna pressured by human activities (Heller 2012). Another explanation could be the existence of diseases that prevented humans or livestock from living in certain areas. This is still true today, as exemplified by locally endemic livestock diseases making large tracts of attractive pasture in Africa unavailable for human settlement. This is a phenomenon unique to Africa (Heller 2012). 

Human Impacts?

Graham and Lundelius (1984) claim that it is unlikely that humans have had much ecological impact on Africa’s megafauna because they have been known to coexist with them for a much longer time than on other continents. Martin (1984) even attributes the lower extinction rates to lower prey naiveté as a result of adapting to the hunting styles of humans. However, the human impact cannot be underestimated. Klein (1984) points to archaeological evidence that the humans of the late Pleistocene/Holocene transition were much more competent hunters than earlier humans. For example, studies of archaeological sites of earlier humans have found that eland (a type of ungulate) remains occur more frequently. Within the archaeological sites of humans who lived in the late Pleistocene/Holocene period (but under similar environmental conditions), remains of wild pigs, which were more dangerous to hunt and therefore required more sophisticated hunting techniques such as traps for example, were more prevalent than those of eland. 

African Wild Pig

The Cape Buffalo Study

A recent paper by Heller et al (2012) using genetic sequencing of African Cape buffalo, a species which has survived from the late Pleistocene period to the present-day, has found evidence of benign human – megafauna interaction during the late Pleistocene. Cape buffalo began a population expansion from 80,000 radiocarbon years ago and reached a peak at 8,000 radiocarbon years ago, which shows that humans and climate change had relatively little impact on the population. This study provides further evidence of benign human-megafauna co-existence during the late Pleistocene. To the extent that Cape buffalo is representative of the ecological dynamics facing other African megafauna, this new research also supports the Graham and Lundelius’ (1984) finding that most of African Pleistocene extinctions occurred in the early Pleistocene. If Klein is correct, this was at a time when human hunters were very poorly technologically developed. Thus, climate change would be the larger factor impacting megafauna populations in Africa. 

Cape Buffalo

Klein, R. G. (1984) ‘Mammalian extinctions and Stone Age people in Africa’ in Martin, P. S. and Klein, R.G. (eds.) Quaternary Extinctions, Arizona: Arizona University Press, pp. 553 – 573

Graham, R. W. and Lundelius, E. L. (1984) ‘Coevolutionary disequilibrium and Pleistocene extinctions’ in Martin, P. S. and Klein, R.G. (eds.) Quaternary Extinctions, Arizona: Arizona University Press pp. 223 – 249

Heller, R. et al (2012) ‘Cape buffalo mitogenomics reveals a Holocene shift in the African human–megafauna dynamics’, Molecular Ecology, 21, pp. 3947–3959

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