The Influence of Climate, Cattle Density and Lake Morphology on Sporormiella Abundances in Modern Lake Sediments in the U.S. Great Plains
Parker, Nancy E.
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Sporormiella, a genus of coprophilous fungus, is increasingly used as a qualitative proxy for megafaunal density. Decreased spore abundances in late-Pleistocene and Holocene sediments are thought to signal prehistoric megafaunal population declines and extinctions. However, much remains unknown regarding the dispersal, deposition, and preservation of Sporormiella, hindering interpretation. Here we investigate the effects of climate, basin characteristics, and cattle density on the representation of Sporormiella in modern lake sediments. We collected surface sediment samples from 24 lakes in a west-east transect across South Dakota, Minnesota, and Wisconsin to test whether Sporormiella abundances varied along a precipitation gradient and areas of varying grazing intensity. Pollen and spores were counted from samples taken at the margin and the deepest point of each lake. Unlike other pollen types, relative abundances and concentrations of Sporormiella spores were uncorrelated between lake-center and lake-margin samples. For lake-margin samples, Sporormiella relative abundances positively correlated with basin variables, i.e. shoreline proximity, lake depth, and lake area. The positive relationship between shoreline proximity and Sporormiella abundances differs from prior reports that Sporormiella concentrations decrease away from shoreline. For lake-center samples, Sporormiella relative abundances were negatively correlated with precipitation and positively correlated with temperature. County-scale cattle density is positively correlated with Sporormiella relative abundance for lake-margin samples in a multiple regression model with shoreline proximity as another predictor, suggesting a highly localized signal of megaherbivore density on Sporormiella. These results suggest that Sporormiella representation in lake sediments is controlled by multiple factors, including but not limited to megaherbivore density.
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