UMD Biology Seminar
Feb. 27, 2015
Dr. Nate Nibblelink, Asst. Professor, University of Georgia
Title: Cascades and Connectivity: The Influence of Spatial Scale on Understanding Ecosystem Processes
Abstract: Spatial ecology addresses how space effects ecological phenomena. In this talk, I will highlight how research in my lab takes advantage of a variety of spatial models to examine how spatial relationships (with special attention to scale) can affect ecological patterns and processes primarily using examples from two forest ecosystems. First, gray wolf (Canis lupus) recovery in the Great Lakes region is anticipated to generate a top-down trophic cascade by altering white-tailed deer density, habitat selection, and foraging behavior. To detect the signal of top-down effects, we sampled understory vegetation in white cedar wetlands in Wisconsin across a gradient of wolf occupancy. Sampling at multiple scales revealed that measurement scale affected our ability to detect relationships between wolf occupancy and species richness of forbs (1-100 m2), and shrubs (10 - 1000 m2). Further, models of local and landscape variables known to affect understory community diversity were much stronger when a wolf occupancy variable was included than when it was not. Evaluated collectively, our results provide little support for either bottom-up or non-trophic hypotheses, but are consistent with wolves triggering a top-down trophic cascade. Second, ecosystem connectivity via transport of nutrients across boundaries can impact ecosystem function and community diversity. Piscivory by coastal river otters (Lontracanadensis), and their use of latrine sites in coastal forests in Prince William Sound (PWS), AK, provide a pathway for nutrient transport between sea and land. Otter use of latrines has been linked to changes in density of understory plants and increases in leaf area index and tree diameter. Understanding dynamics of latrine site use is therefore key to predicting coastal forest change due to declines in schooling fish populations in PWS. Isolating the spatial scale of measured variables was critical for detecting and predicting latrine site selection by otters. Boundary convexity (between sea and land) measured using a 100m moving window was the strongest variable influencing otter latrine site selection. Using the latrine selection model and a suite of additional otter behaviors, we used a spatially-explicit individual-based model (IBM) to explore how nutrient transport processes may respond to changing forage fish populations.