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Dr. Erin Zylstra, Michigan State University
February 20 @ 3:00 pm - 4:15 pm MST
Seminar Title: Using Hierarchical Models to Understand Dynamics of Wildlife Populations: Characterizing Survival and Occupancy of a Desert Amphibian
Abstract: Characterizing variation in the distribution and demography of species is fundamental to addressing an array of ecological questions. Our ability to make these types of inferences depends on data from field-based surveys, which are challenging to collect when species are rare or difficult to observe. Recent advancements in quantitative ecology enable researchers to ask novel questions about population dynamics, to account for imperfect surveys, and to leverage data from diverse sources, including long-term monitoring programs and large-scale volunteer-based efforts. To illustrate how hierarchical models can provide valuable insights on dynamics of threatened species with data collected over multiple temporal and spatial scales, I will highlight a collaborative project focused on lowland leopard frogs (Lithobates yavapaiensis) in Arizona. We used 22 years of survey data to develop a spatially-explicit dynamic occupancy model that allowed us to assess how climate and wildfires influenced the distributional dynamics of leopard frog metapopulations. To increase our mechanistic understanding of how demographic processes contributed to extinction events, we used capture-recapture data to explore associations between adult mortality and hydrologic conditions. We found that survival rates were positively associated with surface-water availability and persistence was higher at sites with perennial water. Drought decreased both the number of potential dispersers and the probability that dispersing individuals were able to colonize unoccupied sites. Similar applications of hierarchical models can help ecologists understand better the ecology of a wide array of species, and the increasing availability of broad-scale and long-term datasets will continue to expand the scope and complexity of questions that they can address.