A primary focus of the lab is understanding the factors shaping communities through time (see my recent paper with Steve Jackson), and in particular trying to tease apart the relative impacts of climate and species interactions on assemblages. For example, do climate change or biotic interactions more strongly influence communities and under which situations? How can we best model past and future changes to biological communities with climate change?

To examine community dynamics more fully, we using a variety of different approaches in different systems: California mammals, fossil pollen, and marine lakes (so far). This approach of looking at similar questions across different systems allows us to determine the context-dependence of our results and also keeps us on our toes!

California mammals

Building off of previous research in the northern Sierra, most of the current and future work in the lab focuses on building a network of sites that span latitudinal and altitudinal gradients and thus capture a diverse array of mammal communities across space and time. Responses to environmental change can manifest in many different ways, so no single proxy or approach is going to adequately characterize ecological or evolutionary changes. Our approach is to tackle the questions with many different tools: the fossils and assemblages themselves, molecular tools, and modeling approaches. More on this project as it develops!

• Northern California assemblages: Graduate student Eric Williams is focusing on understanding the factors responsible for mediating community assembly in California mammals. This builds on Jessica’s dissertation work with Liz Hadly at Stanford. Read more about Eric’s work here.
• La Brea small mammals: A new project in the lab is to examine small mammal assemblages from the La Brea Tar Pits and link their structure and dynamics to other elements of the ecosystem. This is a collaborative project with Jacquelyn Gill, Justin Yeakel, and the La Brea Tar Pits and Museum, and is being led at UC Merced by ES graduate student Nate Fox. More about this project here.
• Southern Sierra mammal communities: Jessica has also been exploring caves in Sequoia-Kings Canyon National Park for woodrat midden deposits. This work seeks to understand how mammal species and communities in the southern Sierra Nevada have responded to climate change over the past 21,000 years (since the Last Glacial Maximum). Have species shifted ranges, and if so, in directions consistent with climate change and their niches? Were there consistent differences in the responses of generalist vs specialist mammals? How strongly are particular species tied to climate change? Were there genetic consequences to range shifts?

Fossil pollen assemblages

Jessica’s postdoctoral research with Jack Williams at UW Madison showed that climate greatly structured turnover in fossil pollen assemblages across space and time. But it wasn’t the only factor explaining turnover, which led to two subsequent projects examining the community structure and species co-occurrence patterns.

• Which kinds of modeling approaches best project patterns of species distributions and assemblage structure across space and time? We are interested in whether different modeling approaches (stacked species distribution models vs. community level models) are more or less suitable for projecting species distributions and assemblages through time. Postdoc Kaitlin Maguire has been leading this effort.
• ETE working group: To more closely examine the role of potential species interactions in structuring fossil pollen assemblages, Jessica works with Kay Behrensmeyer, Kate Lyons, Nick Gotelli, and the rest of the ETE group at the Smithsonian NMNH. The first project detected pollen taxon-pairs that showed significant spatial associations and determined 1) whether they represented potential species interactions or could be explained by climate or dispersal limitation and 2) how stable the association was through time. This project led to an Ecography paper and, together with datasets from other systems, a synthesis to examine the generality of the patterns observed in the pollen data.

Palau marine lakes

A final project that falls under the general heading of “Community dynamics” is work that Jessica is collaborating on with Mike Dawson, Mike Beman, Julian Sachs, and Simon Haberle in Palau. We are using marine lakes in Palau as a model for island biogeography and assessing the degree to which parallel processes give rise to parallel patterns in taxonomic, functional, and genetic diversity of microbes and macrobiota. More here!

Importance of biotic interactions

To set the stage and put the present-day focus on biotic interactions into a broader context, Jessica reviewed the influence of climate change on biotic interactions, focusing on past, present, and future episodes of climatic and ecological change. This paper was done in collaboration with Phoebe Zarnetske, Matt Fitzpatrick, and Seth Finnegan– a diverse group of folks spanning the spectrum from deep-time paleo (Seth) to Cenozoic/Quaternary paleo (Jessica) to modern and future (Phoebe and Matt). One pattern that emerged was that climate change can alter biotic interactions in highly complex ways, so if we don’t incorporate them when we’re anticipating future changes, we’re missing a big piece of the puzzle.