Technical description: The goal of this project is to test three models of faunal change in response to biotic and abiotic forcings during the transition to the modern grassland ecosystem in the Great Plains over the last 4.5 My: the Red Queen, the Court Jester, and the Equilibrium Theory of Island Biogeography. In doing so, we will answer four specific research questions: 1) Do long-term changes in local habitat or climate control taxonomic diversity dynamics? 2) Does climate change associated with the onset of Northern Hemisphere glaciation at 2.5 Ma impact diversity dynamics or the ecological structure of communities? 3) How do catastrophic events (major ashfalls) impact diversity dynamics and ecological structure of communities? 4) How are immigrant species accommodated in the ecological structure of the contemporary community? We will analyze diversity dynamics with an existing database of species occurrences in the Meade Basin, SW Kansas in relation to reconstructions of local paleoecology, paleoenvironment, and paleoclimate. We will characterize ecological structure of communities with body sizes estimated from tooth dimensions and trophic categories reconstructed from carbon isotope compositions of tooth enamel using laser ablation isotope ratio mass spectrometry and a novel combination of morphometric analyses based on high resolution microCT scans. Interpretation of paleodiet proxies will be constrained by isotopic and morphometric analyses of modern species with known diets and habitats from existing museum collections and live trapping in grasslands around Meade, KS. Paleoenvironmental and paleoclimatic reconstructions will be based on a comprehensive suite of proxies measured on paleosol carbonates and bulk sediment samples collected in stratigraphic association with known fossil sites and major ashfalls: carbon isotope ratios of bulk organic matter, carbon and hydrogen isotope ratios of leaf wax n-alkanes, lignin phenol ratios, plant phytolith assemblages, carbonate clumped isotope paleothermometry, and paleosol elemental geochemistry and mineralogy. Paleoclimate proxies and isotopic data will be compared to output of regional scale, isotope-enabled paleoclimate simulations under various forcings. Finally, we will construct ecological niche models for modern mammal species and genera in the region and use paleoclimate model output to test how climate change may have forced range shifts and taxonomic turnover in the Meade record.
Non-technical description: Understanding the origin of modern communities is a fundamental goal of ecology, but reconstructing the history of communities that include species with stratigraphic durations on the scale of hundreds of thousands to millions of years necessarily requires data from the fossil record. Similarly, inferences about the paleoecology of past communities are most robust when informed by data from both living and fossil populations of extant species. Despite the logical connections between ecology and paleoecology, relatively few studies have bridged the gaps in the characteristic observational timescales and methodologies of these disciplines to achieve a comprehensive view of the long-term evolution of specific modern communities. The need to bridge these disciplinary gaps is increasingly pressing in the face of anthropogenic climate change and uncertainty about the magnitude and direction of responses by local communities. This project will examine the ecological, environmental, and climatic context of the origin of the modern small mammal community in the grasslands of the central USA over the last five million years. We will test the effects of both biological and non-biological factors on long-term taxonomic turnover and ecological change in a stratigraphic sequence of local communities using a combination of ecomorphology, biogeochemistry, paleoclimate modeling, and biogeography. This project will link evolution, ecology, and paleoecology with biogeochemistry to trace the emergence of a modern ecosystem over geological time.
