Global warming and human hunting at the end of the Pleistocene led to the extinction of most of the mammalian fauna larger than 44 kg. While the causes of the extinction event are debated and of intense interest, the effect of the ensuing community changes on species that survived the extinction has not been well investigated. Yet knowledge about effects on survivors will be immensely valuable to predictions of future biodiversity. Thus, instead of studying the Pleistocene extinction solely from the perspective of why species went extinct, PIs are keen to investigate how, or in fact, whether, surviving species were affected by the extinction event. PIs therefore propose to use the rich but untapped Quaternary fossil resources of Shasta County, California, to investigate the response of the mammal species that survived the Pleistocene-Holocene transition event. Their primary goal is to determine community, species, and population response of survivors to the Pleistocene-Holocene transition and to sort out whether the response was due to megafaunal extinction, climatic change or both. To document the nature of late Quaternary disturbance events and impacts on the biota, they will use an interdisciplinary approach, based on tracing changes in morphometrics, isotopes, genetics, and community composition of fossil mammals. This will be facilitated by (i) excavations and analyses of newly discovered and known fossil sites; (ii) obtaining secure stratigraphic control with multiple radiocarbon dates and other geochronologic and stratigraphic techniques; (iii) conducting genetic analyses aimed at detecting signs of population subdivision, density changes and local extirpation; (iv) comparison of pre- and post-extinction communities in terms of taxonomic composition, total species richness, species richness within various size and trophic categories, abundance and evenness of species; (v) tracing phenotypic changes in populations; and (vi) using ancient DNA with phylochronologic techniques to directly recognize genetic structuring of fossil populations. All of the biotic changes will be interpreted within the framework of the extensive extinction and climatic changes that are documented in their study area and globally.
