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megafaunal extinction began about 1,000 years after people crossed the Bering Land Bridge
from Eurasia approximately 13,000 years ago, and continued over a period of about 2,000
years. More than 50 species, including mammoths, mastodons, horses, giant ground sloths,
American camels, lions, and the sabre-tooth cats were wiped out (Elias and Schreve 2007).
Numerous lines of evidence suggest that humans, rather than climate, are likely to have been
the major driver of extinction in North America (Johnson 2009, Prescott et al. 2012). Most of
the extinctions occurred during a cold period, known as the Younger Dryas Event, which
interrupted the warmer conditions of the early Holocene. Spore data suggests that megaher-
bivore decline had already begun before the Younger Dryas, and their abundance did not
rebound when climatic conditions reversed (Robinson et al. 2005). The abundance of mam-
moths continued to decline even when spruce, their preferred habitat, was increasing (Rob-
inson et al. 2005, Johnson 2009). Furthermore, simulations of the potential distribution of
extinct North American mammals suggests that the area of suitable climate space for mam-
moths and some other species has expanded in the Holocene compared with the Last Glacial
Maximum (Martinez-Meyer et al. 2004, Svenning et al. 2011). It is thought that the Clovis peo-
ple, armed with efficient spear technology and co-operative hunting skills, had a catastrophic
effect on megafauna, which were probably particularly vulnerable to hunting as they did not
co-evolve with human hunters, and were already limited by indigenous carnivores (Koch and
Barnosky 2006). Species that were more difficult to hunt, such as nocturnal animals, were less
prone to extinction (Martin 1984, Ripple and Van Valkenburgh 2010).
In Australia, megafaunal extinctions occurred when temperatures were fairly stable,
though aridity and human impact may have acted together in reducing habitat suitability,
increasing the vulnerability of megafauna to on-going hunting pressure and environmental
change (Trueman et al. 2005, Wroe and Field 2006). Giant ripper lizard, saw-toothed croco-
dile, giant ratite birds, giant wombats, giant wallabies, marsupial 'lions, and giant and short-
faced kangaroos all became extinct (Elias and Schreve 2007). In Eurasia, interacting climate
and human factors likely drove extinctions, with a larger role for climate than on the other
continents (Nogués‐Bravo et al. 2010, Prescott et al. 2012). For example, model simulations
show a strong, climate-driven decrease in range availability for woolly mammoths in inter-
glacial periods. However, climate and habitat change is likely to have made Eurasian maga-
fauna more vulnerable to human impact in the early Holocene, and thus human impact
most likely played a role as well (Nogues-Bravo et al. 2008, Pushkina and Raia 2008, Sven-
ning et al. 2011).
Africa is exceptional in having few Pleistocene extinctions and retaining a relatively intact
megafauna, though Pleistocene elephants, Pleistocene camels, and Pleistocene bison were
lost (Elias and Schreve 2007). The resilience of African megafuna is possibly due to co-
evolution of humans and their prey, as well as less severe climate impacts (Nogués‐Bravo
et al. 2010). Studying the effects of extant African megafauna can provide clues as to how
megafaunal extinctions might have impacted ecosystems elsewhere. It is clear that ele-
phants (see Chapter 2) and other African megafauna have massive effects on ecosystem
structure and function, shaping the distribution and abundance of trees, influencing fire
regimes, facilitating seed dispersal and germination, and increasing nutrient cycling. These
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