PALEONTOLOGICAL BASELINES OF DIVERSITY AND TURNOVER FROM THE MAMMALIAN FOSSIL RECORD

One of the main challenges facing conservation biologists and planners is to understand the long-term normal range of ecosystem properties and processes. Comparing modern ecosystems to their historical baselines provides a basis for assessing the scope of human impacts, alternative ecosystem states, reaction times of populations to disturbance, and possible targets for population and ecosystem restoration. The fossil record extends the written and archeological records of historical baselines into geologic time.

I present geohistorical trends in species diversity and turnover, in response to climate change, from the Cenozoic mammalian record with relevance for ecosystem changes of today. Data are from dense Miocene and Quaternary records of mammalian faunas in South Asia and North America. For mammals, paleontological baselines indicate that immigration, environmental filtering, and geographic-range shifts are normal processes. In the Miocene Siwalik record of South Asia, climate change had a major impact on faunal composition and structure with the dynamics of faunal change depending on the magnitude, direction, and duration of climate change. Large magnitudes of climate change caused major habitat transformation and substantial turnover of species. Today, habitat loss and transformation pose greater threats than invasive species for continental faunas and are the primary cause of extinction and endangerment. During glacial cycles of the Quaternary, most species of mammals experienced range shifts of several hundred km with little extinction. Geographic ranges will continue to shift in response to anthropogenic climate change. Data from modern ecosystem and the fossil record indicate that species need biodiverse habitats for dispersal and recolonization. This requirement has clear implications for the kinds of landscape-level strategies that will succeed or fail in conserving species and ecosystems.