Understanding species and community responses to past and future climate change
Successful conservation depends on a solid understanding of how climate change and biological interactions regulate biodiversity across both space and time, so that the distribution of species, communities, and ecosystems can be accurately predicted in responses to future climate change. Because species tend to respond to environmental changes in an idiosyncratic manner, it is difficult to generalize and predict biodiversity patterns for the future. The main goal of this dissertation is to increase our understanding of the effects that climate change had on species and communities in the past so that we can use the observed and estimated responses (from models and empirical data) to better inform our predictions of how species and communities may respond to climate change in the future. To complete this goal, I first examined the patterns of mammalian range shifts during the late Quaternary and estimated how the velocity of climate change and the dispersal ability of a species affects the magnitude of species range shifts in response to climate change. Findings from this research show that the broad pattern of species range shifts are poleward, but overall, species respond to climate change with a multidirectional response. Species are also projected to shift their ranges at a much faster rate in the future when compared to estimated past range shifts. The factors estimated to increase past rates of range shift are the velocity of temperature and precipitation change, while species traits appear to determine shift rates in the future. I next examined the factors associated with the assembly of small mammal communities since the Last Glacial Maximum and determined if those factors changed over time in relation to climate change. Using species distribution models and the fossil record, I determined if small mammal communities preserved in a fossil deposit in northern California at various time periods in the past assembled as a function of environmental filtering or competition. Results suggest that climate (environmental filtering) plays a large role in determining the species composition of a community in any given time period, but under certain scenarios competition could be an additional determinant for the integration of single species into the community. Lastly, I examined how mammalian communities in North America are expected to change in the future as a response to anthropogenic climate change. I examined this question using stacked species distribution models and projected these models into two future time periods and under two different representative concentration pathways. Results from this study suggests that large areas of the southeastern US and the deserts of the southwest will lose species, on average, while the Rocky Mountains and the interior portion of Canada will gain species. I also determined that large areas of Canada are expected to harbor novel mammalian communities as species respond individualistically to climate change. Overall, by examining the factors that drive specie range shifts, examining processes important to community assembly patterns, and estimating species responses to future climate change, I have generated findings that are valuable for efforts to develop conservation strategies around the globe. Research from this dissertation is also one of first examinations of the development of novel mammalian communities in North America as a response to future climate change over a large spatial scale, and the results from this study will be important in providing conservation managers with areas of potential diversity loss and change in the coming future.