A COMPARISON OF PLANT AND MAMMAL COMMUNITY STRUCTURE FROM DEEP TIME TO THE RECENT

Understanding the structure, function, and dynamics of ecological communities is a central goal of ecology. Models of extant ecosystems hold that biodiversity is a buffer that helps stabilize ecosystem processes and services. When viewed over the entire Phanerozoic, modern levels of diversity and species richness are a relatively recent phenomenon in terrestrial communities. Many Mesozoic and older communities are considerably less diverse than those of today and yet demonstrate patterns of species composition, dominance and diversity patterns, and architectures that parallel those of modern ecosystems. Here, we analyzed one measure of community structure, the strength of species associations, in replicated plant and mammal communities from ~322 Ma to the present. Preliminary results indicate striking differences in the species associations of plants and mammals: on average, 60% of the associated pairs of fossil plant taxa showed positive associations through evolutionary time, whereas only 30% of associated mammal species pairs exhibited such associations. This result is particularly striking because the plant communities included in the analysis are very different taxonomically. In contrast mammal associations are considerably more variable and less positive through time. We investigated the variability in mammal communities further by analyzing the species associations of large mammal communities in Africa across the Plio-Pleistocene. We hypothesized that climate variability would affect species associations and predicted that during times of greater climate variability and therefore more patchily distributed resources, we would find stronger positive associations because species would be restricted to these isolated patchy resources. The trend is statistically significant (Spearman’s rho = 0.825, p < 0.001) and suggests increasing provinciality (i.e., habitat tracking of increasingly patchy resources) in response to greater environmental variation. These null models suggest a fundamental difference in the community structure of plant and mammal communities.

Additional co-authors: Gene Hunt, Carlos Jaramillo, Nathan Jud, Conrad C. Labandeira, Cindy V. Looy, Angela T. Moles, Richard Potts, Hans-Dieter Sues, Rebecca C. Terry, Ethan P. White, John J. W. Williams, Scott L. Wing