COMMUNITY ECOLOGICAL CONTEXT PLAYS A ROLE IN PREDICTING RESPONSES OF INDIVIDUAL SPECIES TO CLIMATE CHANGE DURING THE PALEOCENE-EOCENE THERMAL MAXIMUM

Contemporaneous suites of closely related and similarly adapted species might be expected to have similar evolutionary responses to climate change based on their similar interactions with the abiotic environment. However, much as the Red Queen hypothesis proposes that biotic interactions can influence community composition and species longevity over long timescales, changes in community ecology may also play a role in predicting the responses of individual species during climate change. The Paleocene-Eocene Thermal Maximum (PETM), a rapid (~170 ky) global warming event ~56 million years ago is an exemplary system for testing such questions because a rich flora and mammalian fauna are preserved throughout an interval in which mean annual temperature warmed by ~5-10 °C during a relatively brief onset (~13 kyr), remained high for ~115 kyr, then recovered to cooler climatic conditions over ~42 kyr. To evaluate the potential role of community ecology in climate change response, we documented patterns of morphological change in the molars of three small-bodied, insectivorous mammalian species that have been proposed to be closely related across the PETM. If patterns reflected a community-mediated, indirect response to climate change, then morphological change should be concentrated at the PETM boundaries when flora and mammalian fauna were fundamentally reorganized. In contrast, if patterns reflected a direct response to abiotic climate change, then additional change should be detectable in conjunction with documented shifts in temperature and aridity within the PETM. We found significant differences in molar crown shape across PETM boundaries, but not within the PETM, for both lineages that range through the event. When morphology is quantified in terms of molar crown area, an established proxy for body mass in mammals, only one of the three species appears to have changed significantly across the focal interval. That individualistic pattern of body size change is further consistent with communities of insectivores whose responses to climate change are indirect and community-mediated, not directly linked to abiotic climate change.