Causes of Ecosystem Transformation at the End of the Pleistocene: Evidence from Mammal Body-Mass Distributions

Animal body sizes reflect the discontinuous architecture of the landscapes in which they live, and consequently their body-mass distributions are distinctly clumped rather than continuous. This architectural discontinuity is generated by ecological processes that discretely operate over micro-, meso-, and macroscales. Therefore, changes in these important scale-specific processes for a given geographical region over time should be reflected by corresponding changes in faunal body-mass clump patterns. In this study, we utilized this hypothesis to investigate the terminal Pleistocene mammal extinction event. Specifically, we analyzed the body-mass distributions of latest Pleistocene and modern mammal faunas from northern Florida and southern California to determine the nature of any changes in the clump structures of these regions during the Pleistocene–Holocene transition. In both regions, despite their wide geographical separation and faunal distinctiveness, body-mass clumps below the 40-kg level were remarkably stable across the Pleistocene–Holocene transition despite suffering extinctions. Larger clumps, in contrast, were either orderly truncated or completely eliminated rather than chaotically fragmented. Based on these findings, we argue that the terminal Pleistocene mammal extinctions were caused, at least in part, by changes in key mesoscale aspects of the landscape crucial to supporting a diversity of large mammals. Received 23 April 1997; accepted 14 October 1997.