Thursday, August 7, 2008 - 3:40 PM

COS 92-7: A new human predation model for late Pleistocene megafaunal extinction patterns in North America

Jeffrey V. Yule, Louisiana Tech University, Christopher X. J. Jensen, Pratt Institute, and Aby Joseph, SUNY Stony Brook.


Although Late Pleistocene extinctions disproportionately affected larger mammalian species, a variety of smaller species were also lost. To date, no explanation accounts for observed size-based extinction patterns among both larger and smaller species. Beginning with the assumption that human predation caused the extinctions, we offer the first such explanatory hypothesis. We hypothesize that the ratio-dependent functional response represents a more realistic depiction of long-term predation and that its use could account for this as yet unexplained extinction pattern. We then test the hypothesis via a one-predator, six-prey differential equation model using Mathematica.


Results indicate that significantly altering functional response assumptions, which represent a cornerstone of ecological modeling, fails to produce qualitative differences in survival-extinction outcomes over existing models. This unexpected finding suggests that the ecological characteristics of Late Pleistocene extinctions remain insufficiently understood to distinguish between a variety of competing extinction scenarios—including those involving only human predation or multiple causes in combination (e.g., human predation and climate change). Although we find no support for the hypothesis we present, in light of the current limits of parameterization, our results indicate that we are also unable to falsify it. We conclude that the matter of causation and the conclusions of previous Late Pleistocene extinction models remain far less certain than many have assumed.