Mammalian beta diversity in the Great Basin, western USA: palaeontological data suggest deep origin of modern macroecological structure

Aim Recent work indicates that desert assemblages have elevated beta ( β ) diversity (between-locality turnover of species composition). This study compares β diversities between the Great Basin and the Great Plains of the western USA over the last 17 Myr. Today, the Great Basin is a topographically diverse desert scrubland to woodland and the Great Plains are low-relief temperate grassland, but 17 Ma they were more similar in topography, climate and land cover. A georeferenced database of mammal occurrences, complied from several sources, is used to test two hypotheses for the elevation of Great Basin β diversity: (1) that tectonic change of the topography has driven increased habitat packing in highand low-elevation habitats, and (2) that climatic cycling in the Pleistocene has driven faunas from neighbouring provinces to overlap in the region. Location The Great Basin of the USA, centred on Nevada, and the central Great Plains of the USA, centred on Nebraska. Methods Mammalian faunal lists compiled from published records and the records of many museums, available online, were partitioned into time-slices ranging from the recent to 17 Myr old. Beta diversity was calculated for each time-slice in two ways: multiplicative β diversity using first-order jackknife richness, and additive beta diversity using Simpson’s evenness. Results Beta diversity is elevated in Nevada relative to Nebraska today. Beta diversity has been higher in the Great Basin since the Pleistocene and possibly since the late Early Hemphillian ( c . 7 Ma). Beta diversity in the Late Barstovian ( c . 13.5 Ma) of the Great Plains was higher even than β diversity in the Great Basin of today. Main conclusions The elevated β diversity in the Hemphillian supports the tectonic change hypothesis. The patterns of β diversity in the Recent, Pleistocene and Hemphillian all suggest that local-scale processes are important. The β diversity of the Late Barstovian Great Plains supports other studies indicating increased primary productivity or species packing.