Tracking Urbanization's Impact on Bird Functional Diversity Over Time

Abstract

Introduction: Urbanization drives major changes in the natural environment and its role in bird diversity decline has been the focus of extensive research. Most studies assess the effects of anthropogenic stressors on biodiversity using a space-for-time substitution, examining urbanization levels across a gradient from rural to highly urbanized environments. In contrast, this study investigates how different levels of urbanization change affect bird diversity through time. My goal is to determine whether a temporal approach yields results similar to or different from those found in space-for-time substitution studies. Methods: The study region includes Indiana, Ohio, and Kentucky, encompassing the metropolitan areas of Indianapolis, Columbus, Cincinnati, and Louisville. Using eBird data, I first developed Species Distribution Models (SDM) to generate predictions of bird presences and absences for 134 species in two time periods: 2013 and 2023. Using these predictions, I then assessed bird diversity using four metrics: species richness, functional richness, functional evenness, and functional divergence. The latter three metrics were derived by analyzing the trait space, an n-dimensional representation of species' traits that influence how species interact with and shape their environment. All avian diversity metrics were obtained for each year for each 3kmx3km site across the study region. I used NLCD impervious surface data to quantify change in urbanization. Change in avian diversity was then modeled as a function of change in impervious surfaces. Results: Model results indicated that functional richness decreases with increasing levels of urbanization. Specifically, sites with medium and high levels of urbanization change saw the most dramatic declines in avian functional diversity. In contrast, I found that increasing urbanization led to increases in species richness. Specifically, sites characterized by medium change in urbanization have seen larger increases in species richness compared to sites characterized by no change, low change, or high change in urbanization. Finally, sites with high levels of urbanization had an increase in functional evenness and functional divergence compared to sites with no change in urbanization. Conclusions: Findings of declining functional richness and increasing species richness with increasing temporal change in urbanization corroborate findings from previous space-for-time substitution studies that focused on spatial urban gradients. These replicated patterns provide justification for using the space-for-time substitution as a proxy for temporal change in urban development and thus for assessing the effects of urbanization on avian diversity change. By reinforcing the findings of previous studies, my work broadens our understanding of urbanization’s impact on biodiversity and provides a blueprint for urban developers and conservation managers to ensure that adequate habitat for birds is preserved during urban development.No embargoAcademic Major: Data Analytic