THE ROLE OF FUNCTIONAL TRAITS IN MAMMALIAN COMMUNITY STRUCTURE ACROSS THE PLEISTOCENE-HOLOCENE TRANSITION

The study of communities over time allows us to evaluate the degree to which ecological processes are affected by climate change and human activity. Such knowledge is critical to predicting how species will assemble into communities in response to future climate change. Recent work documenting the co-occurrence structure of communities over the past 300,000,000 attributed a shift from aggregated (species that occur together more frequently than expected by chance) to segregated (species that occur together less frequently than expected by chance) species pairs in the mid-Holocene to human impacts. Here, we investigate the complex role of climate and species traits in the co-occurrence structure of mammals across the late Pleistocene to the modern. We find that the climate change and biodiversity loss at the terminal Pleistocene fundamentally changed species associations: extinct species were more likely to form significant pairs than surviving species, and moreover, those pairs were more likely to be positive associations. The interaction strength of pairs that contained an extinct species was different for aggregations, but not segregations suggesting that the loss of the megafauna had differential effects on the co-occurrence of surviving species. Specific species traits such as body mass or trophic interaction declined in their importance or switched from promoting aggregations to promoting segregations. We conclude that future climate change and extinction are likely to exacerbate these trends.