Eric Williams

Ecology, Paleoecology, and Biogeography


With the rate of future climate change expected to be more rapid than any event observed since the late Quaternary, it is essential that we understand how species will respond and react to estimated changes in climate. Understanding how species have responded to changes in the Earth’s climate is essential if we are to correctly predict and develop effective conservation methods for species in the future. My current research focuses on understanding how past climate change has affected species, so that we can use these observed responses to better inform our predictions of how species may respond to future climate change.

Estimating Species Range Shifts as a Response to Past and Future Climate Change:

Species have been shown to exhibit a vast array of responses to climate change. Of the possible responses, range shifts have been examined in great detail using both modern and fossil data. These data show that in general, species exhibit individualistic responses to climate change as they track their climatic niche across the landscape. This individualistic response is hypothesized to be driven by the individual climatic tolerances of a species. If this is the case then species should shift their ranges according to the rate of climate change and the distance in which they are capable of dispersing. My research estimates the patterns of species range shifts in North American mammals in response to past and future climate change using species distribution models. My work examines how the velocity of climate change and a species dispersal ability determines the extent in which a species will shift its range in response to climate change.

Processes Driving Community Assembly Patterns in Small Mammals of Northern California:

The importance of neutral (i.e. ecological drift) and non-neutral (i.e. climate filtering and biotic interactions) processes on the composition of communities is often debated. The relative importance of different processes can vary depending on the scale of the study, species pool size, and the nature of climate or habitat change experienced by a community. However, it is difficult to predict which processes are important under specific scenarios, making it difficult to determine how species will assemble into communities as they respond to future climate change. My research assesses the relative importance of climate and functional similarity in facilitating the assembly of small mammals from a fossil deposit located in Northern California, which spans the previous 17,500 years. Here I construct species distribution models to generate climate-based predictions of community composition in all time periods throughout the fossil deposit and compare the predicted community to the fossil community in each of the time periods; matches and mismatches are attributed to climate, interactions, or other processes. I then examine the possibility of biotic interactions in determining the community composition at the fossil location. By determining the community trait values and comparing that to individual species I can determine the possibility of competition occurring in the system and its importance in shaping the composition of a community during a time period.

Changes in Small Mammal Phylogenetic Diversity as a Response to Climate Change:

Global biodiversity is expected to change at unprecedented rates over the next 100 years, largely suggested to be the result of anthropogenic climate change. Therefore, understanding how biodiversity changes in response to climate change is important if we are to mitigate and minimize biodiversity loss in the coming future. Classic measures of biodiversity include measures of species richness, taxonomic ratios, and diversity indices. These measures, however, classify all species as equal ecological units, contributing the same amount of diversity to an ecosystem or community, and does not take into consideration a species evolutionary history or ecological differences. This can make it difficult to determine the exact mechanisms that are responsible for observed differences in community structure and diversity. However, there is a recent diversity metric, phylogenetic diversity, which does incorporate the evolutionary history and ecological differences of a species by analyzing a species contribution to the diversity of a community or ecosystem, based on its phylogenetic relationship with all other species in the community. Phylogenetic diversity provides a mechanism to determine species that contribute high levels of diversity, which may be important targets for conservation efforts. However, if we are to understand which species need to be conserved to minimize diversity loss to future climate change, we must understand how phylogenetic diversity changes with climate change. Therefore, my work examines how phylogenetic diversity changes in response to climate change events over the last 18,000 years.  The results from this study aims to fill in knowledge gaps of how phylogenetic diversity changes with climate over long time scales, and can potentially be used to determine how phylogenetic diversity will change in response to future climate change.

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