FUNCTIONAL DIVERSITY OF NORTH AMERICAN CENOZOIC MAMMALS

Abstract

Understanding the structure and function of ecological communities is critical to predicting the effects of climate change and biodiversity loss. Functional diversity uses the role of species in an assemblage and is a key component of an ecosystem’s structure. Rather than using a taxonomic classification, community structure is evaluated using a species’ functional traits, which may be morphological or physiological. Metrics of functional diversity summarize variation in traits within a community. Modern ecological studies find that mammal functional diversity is correlated with climate. In contrast to global species diversity patterns, temperate regions of the globe support higher levels of functional diversity. The responses at regional scales are unpredictable and vary among regions and climatic factors. Functional diversity rises or declines and trait compositions shift. However, mammal communities today are depauperate and highly altered by human impacts. The fossil record provides a unique opportunity to ask how the functional diversity of mammal communities changes over time prior to the influence of humans. We constructed a database of mammalian communities in North America spanning the entire Cenozoic, and ask how functional diversity changes over time. We ask whether functional diversity is correlated with changes in global climate or if archaic mammal communities differed from modern mammal communities. We use four species traits; locomotion, diet, body mass and life habit. We find no correlation between δ18O levels and variation in functional diversity. Functional diversity spiked during the Eocene, a period when archaic orders began to rapidly decline and new orders were immigrating into North America. These results suggest that global climate does not exert strong controls on functional diversity of mammalian communities. Further, species invasions may trigger increased functional diversity and a period of niche exploration. Understanding how different aspects of community structure changes over time and in response to natural invasion or disturbance may lead to more effective.