TESTING PATTERNS OF CO-OCCURRENCE AMONG PLANT AND MAMMAL SPECIES IN COMMUNITY ASSEMBLAGES 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, but how does this play out over geological time? 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. We analyzed the strength of species associations, in replicated plant and mammal communities from ~300 Ma to the present. We found 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. Despite this difference, we found significant similarities in the factors affecting these patterns of co-occurrence. We evaluated co-occurrences to determine the role of habitat and other environmental factors in shaping both significant species associations and segregations. In general, habitat characteristics are important in explaining spatial patterns of species co-occurrence in both mammals and plants across time. This suggests that habitat requirements and similar responses of species to abiotic factors are driving patterns of community assembly across long time spans. Biodiversity per se thus may be less important in stabilizing ecosystems than species’ successful adaptation to suites of abiotic environmental parameters.