Late Pleistocene Large Mammals that Went Extinct Had No Distinguishing Features
Lorenzen, E. D., Nogués-Bravo, D., Orlando, L., Weinstock, J., Binladen, J., Marske, K.A. and 49 additional co-authors. 2011. Species-specific responses of Late-Quaternary megafauna to climate and humans. Nature 479: 359-364.
Ancient DNA extracted from radio-carbon dated fossil remains of six large-bodied Ice Age mammals were compared to paleoclimatic data on temperature and precipitation and to the distribution of prehistoric humans over the last 50,000 years, with a focus on four critical time periods: 42, 30, 21 and 6 thousand years ago (kya) -- pre-LGM (Last Glacial Maximum), peak LGM, end LGM and mid-Holocene, respectively. Demographic histories for each species were inferred from ancient mitochondrial DNA (control region) sequences that were analyzed three different ways: "Bayesian skyride," serial coalescent simulation and isolation-by-distance analysis.
All of the cold-adapted mammals studied by this research team managed to survive the long, relatively warm period (ca. 50-30kya) that preceded the LGM, apparently by finding small pockets of suitable habitat and climate-refugia-where individuals could persist for centuries in sufficient numbers that once conditions improved (i.e. got colder), populations rebounded. Such bottlenecks were evident in all species except bison. Mammoths, for example, were estimated to have rebounded ten-fold by 26kya, from a low of about 5,000 individuals-evidence that dramatic population declines do not necessarily lead to species extinction.
The wooly rhinoceros was widely distributed across Eurasia but went extinct rapidly during the intense warming that characterized the end of the LGM (about 14kya), with no evidence that humans hunters affected this outcome. Musk ox were similarly more affected by climate than by humans and while their range and population size has contracted, they have persisted despite Holocene warming (Campos et al. 2010). Muskox, like reindeer, have found suitable Holocene refugia across the Arctic: while musk ox numbers are currently rather low, wild and domestic reindeer number in the millions. Woolly mammoth went extinct after the Ice Age ended but more gradually, perhaps due to a combination of climate change and human hunting.
The authors suggest this study has implications for predicting the possible fates of living large-bodied, cold-adapted mammals should forecasted anthropogenic global warming come to pass. It is significant that the study found no distinguishing characteristics in the rate or pattern of decline in those species that went extinct compared to those that have survived and that all six species survived-and rebounded from-marked declines in their populations. As the authors conclude, such outcomes emphasize "the challenges associated with predicting future responses of extant mammals to climate and human-mediated habitat change."
Campos, P.F., Willerslev, E., Sher, A., Orlando, L., Axelsson, E., Tikhonov, A., Aaris-Sørensen, K., Greenwood, A.D., Kahlke, R.-D., Kosintsev, P., Krakhmalnaya, T., Kuznetsova, T., Lemey, P., Macphee, R., Norris, C.A., Shepherd, K., Suchard, M.A., Zazula, G.D., Shapiro, B. and Gilbert, M.T.P. 2010. Ancient DNA analyses exclude humans as the driving force behind late Pleistocene musk ox (Ovibos moschatus) population dynamics. Proceedings of the National Academy of Sciences 107: 5675-5680.