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 landsc apes in which they live, and consequently their body-mass distribution s are distinctly clumped rather than continuous. This architectural di scontinuity is generated by ecological processes that discretely opera te over micro-, meso-, and macroscales. Therefore, changes in these im portant 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 investig ate 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 determ ine 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-ma ss clumps below the 40-kg level were remarkably stable across the Plei stocene-Holocene transition despite suffering extinctions. Larger clum ps, in contrast, were either orderly truncated or completely eliminate d rather than chaotically fragmented. Based on these findings, we argu e that the terminal Pleistocene mammal extinctions were caused, at lea st in part, by changes in key mesoscale aspects of the landscape cruci al to supporting a diversity of large mammals.