Mammal community structure of Sundanese fossil assemblages from the Late Pleistocene, and a discussion on the ecological effects of the Toba eruption

Abstract

The mammal community structure of four Sundanese fossil sites from the Late Pleistocene are examined and compared to those of modern communities. Three sites from Indonesia: Punung, Sibrambang and Lida Ajer show a community structure more similar to each other than to modern Sundanese communities. Niah Caves exhibits a structure entirely consistent with modern communities. Taphonomic bias and lower species richness in the Indonesian sites may be the cause of these differences. However, there is reason to believe that the differences observed are at least in part a result of the environmental conditions under which these Late Pleistocene communities formed. If so, they represent an alternative stable state of community structure to that seen in later and modern communities. If this scenario holds, modern community structure in Sundaland would have formed sometime between 128–118 ka and 45–39 ka. These changes could therefore be the result of the Toba eruption, although it seems more likely they stem from environmental fluctuations accompanying glacial/interglacial cycles. Mammal species in Southeast Asia seem particularly resistant to any effects of the Toba eruption. Particular attention is focused on the orangutan, which, despite being in the immediate vicinity of Toba before and after its eruption, appears to have suffered no significant effects. These observations have implications for theories suggesting the Toba eruption resulted in a population bottleneck and altered the course of human evolution.