Mammalian Responses to Pleistocene Climate Change

A recent paper entitled Mammalian responses to Pleistocene climate change in southeastern Australia (Geology, January 2007, V 35 N. 1, pp 33-36) researchers G. Prideaux, R. Roberts, D. Megirian, K. Westaway, J. Hellstrom and J. Olley

From the abstract:

Resolving faunal responses to Pleistocene climate change is vital for differentiating human impacts from other drivers of ecological change. While 90% ofAustralia’s large mammals were extinct by ca. 45 ka, their responses to glacial-interglacial cycling have remained unknown, due to a lack of rigorous biostratigraphic studies and the rarity of terrestrial climatic records that can be related directly to faunal records. We present an analysis of faunal data from the Naracoorte Caves in southeastern Australia, which are unique not only because of the species richness and time-depth of the assemblages that they contain, but also because this faunal record is directly comparable with a 500 k.y. speleothem-based record of local effective moisture. Our data reveal that, despite significant population fluctuations driven by glacial-interglacial cycling, the species composition of the mammal fauna was essentially stable for 500 k.y. before the late Pleistocene extinctions. Larger species declined during a drier inter­val between 270 and 220 ka, likely reflecting range contractions away from Naracoorte, but they then recovered locally, persisting well into the late Pleistocene. Because the speleothem record and prior faunal response imply that local conditions should have been favorable for megafauna until at least 30 ka, climate change is unlikely to have been the principal cause of the extinctions.

The proposal of the paper is that climatic change alone was not the cause of mammalian extinctions in Australia. This is supported by a review of how regional fauna dealt with climatic cycles as part of an explanatory route towards a resolution of the extinction debate in Australia.

The results of the study suggest that climate had a small hand in population reduction, it was not sufficient to cause the extinctions. The cause itself therefore can be more associated to human involvement:

... the persistence of relatively cool, moist conditions for most of the last glacial should have favored the megafauna, a conclusion com­parable to that drawn from inland localities by Miller et al. (2005). Therefore, extinction of the NCWHA megafauna by ca. 45 ka (Pate et al., 2002) cannot have been caused solely or primar­ily by climate change, especially given the per­sistence of all other mammals into the Holocene (McDowell, 2001). The disparity between pre-human and posthuman changes at Naracoorte resembles that described for an analogous North American mammalian succession in Porcupine Cave, Colorado (Barnosky et al., 2004b). These records show that mammal faunas on both con­tinents were well adapted to Quaternary climatic variations prior to the arrival of humans.

While this has no direct correlation to unknown animals, it does support the successful survival of species in the environment. Humans had the larger impact, and the environment at the time was sufficient to sustain the megafauna.

Craig Heinselman
Peterborough, NH