Middle Pleistocene Glacial-Interglacial Transitions and Their Effect on Mammalian Community Reorganization in Colorado

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This project will finish collecting and will analyze a superb sequence of middle Pleistocene fossil-mammal faunas from Porcupine Cave, located high in the Colorado Rocky Mountains. The fossils and other relevant data will be used to: (1) Identify how high-elevation (2900 m) mammalian communities were reorganized through glacial-interglacial transitions between - 400,000 and 800,000 years ago. (2) Quantify, through computerized imaging and statistical techniques, the climatic signal contained in the biogeographic distribution and spatial morphologic variation of selected extant species that also are present in the fossil faunas. (3) Test five hypotheses about the interaction between climate and mammalian communities. The hypotheses are formulated especially to test whether changes in seasonality are important in triggering major community reorganizations, which is the cornerstone of the coevolutionary disequilibrium model. Testing the hypotheses will rely on comparing the faunal data with independent predictors of past climate, notably oxygen- and carbon-isotope curves (and their attendant implications for global ice volume, temperature, and CO2 levels) and model-generated estimates of seasonality and other climatic parameters. This research is important in identifying how oscillations in specific climatic parameters provoke changes in mammal communities in the absence of human impact. Such information currently is unavailable -- human influence cannot be ruled out of even late Pleistocene commu n ity changes -- and will be extremely useful in predicting what might happen to modern "protected" ecosystems over tens to hundreds of years. Additional significance lies in (1) providing an exceptionally rich sample of the fossil fauna for a time and place where little is known, which in turn yields paleoecologic, evolutionary, and paleoclimatic insights; and (2) refining and developing quantitative techniques for extracting the climatic signal from biogeographic ranges and morphologic variation of mammal species that are present in numerous fossil sites of the American West.