Population dynamics
Characterizing changes in the abundance and distribution of wildlife populations over time, and understanding the mechanisms that underlie these changes, are critical to inform conservation and management decisions. As part of my dissertation work, I collaborated with biologists at Saguaro National Park to better understand the effects of drought and landscape structure on metapopulation dynamics of lowland leopard frogs in arid mountain canyons of southern Arizona. Extinctions of frogs, both at local and metapopulation scales, were associated with drought-related declines in surface-water availability, particularly in canyons that had been inundated with sediment following high-elevation wildfires (Zylstra et al. 2019 Ecological Applications). As part of my postdoctoral work , I'm studying the population dynamics of monarch butterflies in eastern North America. I used data from several large-scale, volunteer-based monitoring programs to identify the relative importance of biotic and abiotic factors, including climate, forest cover, and herbicide use, in observed declines (Zylstra et al. 2021 Nature Ecology & Evolution). Now, I'm building off of that work, forecasting monarch population responses to future changes in climate on the spring and summer breeding grounds. |
Demography
Changes in abundance reflect changes in underlying demographic rates, including survival, reproduction, and recruitment. I'm particularly interested in understanding how these rates vary among individuals and over space and time as a function of climate, anthropogenic activities, and population structure. I've used capture-recapture data to characterize survival in a wide variety of taxa, including reptiles, amphibians, and raptors. For Sonoran desert tortoises, I used 22 years of data, collected across the species' range in Arizona, to better understand the effects of drought and urbanization on adult survival (Zylstra et al. 2013 Oecologia). For lowland leopard frogs, I documented low rates of survival that varied seasonally with surface-water availability based on in-situ photographs of individuals' unique spot patterns (Zylstra et al. 2019 Freshwater Biology). My colleagues and I are also using long-term capture-recapture data to evaluate density-dependent effects on survival of Cooper's hawks in an urban environment. |
Development of statistical models
Increasingly, Bayesian methods and hierarchical models are being used to draw inferences about ecological processes while accounting for imperfect detection and other sources of observation error. I'm interested in developing and extending existing models to provide reliable information for wildlife managers and agencies. Recently, my colleagues and I developed a spatially-explicit model to estimate demography and viability of wildlife populations at fine spatial scales using data from sites located throughout a larger region of interest. We used this model to better understand spatial patterns in survival, transition rates, and viability of Sonoran desert tortoise populations throughout their range in Arizona (Campbell et al. 2018 Ecological Applications). I also developed a model to describe somatic growth of vertebrates that inhabit areas with strong seasonal dynamics based on data collected commonly during capture-recapture studies. I used the model to characterize growth of canyon treefrogs, short-lived hylid frogs that inhabit mountain canyons in the southwestern U.S (Zylstra and Steidl 2020 Ecological Modelling). |