ANTHROPOGENIC INFLUENCES ON BOTTOM-UP AND TOP-DOWN REGULATION OF ANIMAL DISTRIBUTIONS, POPULATIONS, AND BEHAVIORS IN URBAN ENVIRONMENTS

Abstract

Animal populations are simultaneously governed by both bottom-up (e.g., habitat availability) and top-down (e.g., predation) regulation. While ecologists historically sought to differentiate the roles of bottom-up and top-down regulation on ecosystems, the two are not so easily defined in urban ecosystems due to the immense influence humans have on ecological processes in cities. In Chapter One, I present this argument from a philosophical perspective and comment on how this philosophy has shaped my worldview. In Chapter Two, I examine the legacy of historical park planning on urban bird assemblages using archived municipal maps and historical bird data. My analysis found a positive correlation between percent park area and both species richness and functional richness of birds. Additionally, I found the effect size of park area was larger than the effect of certain life history traits thought to facilitate urban exploitation. These results indicate that landscape features and life history traits are equally responsible for the success of synurbic species. Chapter Three explores the effect of urbanization on animal behavior by analyzing anti-predator behavior of white-tailed deer (Odocoileus virginianus) in relation to ambient light, noise, and human activity. Despite negligible predation risk in my study area, deer expressed higher vigilance behavior in dark and noisy conditions, and increased their foraging group size during noisy conditions. These results suggest that anti-predator behaviors are a response to the perception of predation risk rather than a response to the actual presence of predators. Although predation of deer is rare in urban ecosystems, predation of smaller wildlife species by mesopredators, such as non-native domestic cats (Felis catus) is common. Chapter Four examines the potential for predation and zoonotic disease transmission between cats and eight native mammals by estimating the spatial and temporal overlap between species. I found that cat distribution was largely driven by anthropogenic features, whereas native wildlife was generally deterred by anthropogenic features and instead occupied forested areas. I also found that cats, as a species, were active on the landscape during the full 24-hour cycle. As a result, while spatial overlap between cats and wildlife varied across the study area, temporal overlap was possible anywhere cats and wildlife co-occurred. Chapter Five expands on Chapter Four and investigates predation directly by using observations of cats carrying prey documented by motion-activated cameras. I found that predation by cats was higher in areas where supplemental cat food was prevalent, but declined near forested areas. Additionally, my results indicate that cats within 250 meters of a forest edge predominantly preyed on native wildlife, whereas cats generally preyed on non-native rats (Rattus norvegicus) when greater than 250 meters from a forest edge. Each chapter provides applied recommendations to the management and conservation of urban wildlife, but together, my work demonstrates the entanglement of bottom-up, top-down, and anthropogenic forces in urban ecosystems. In light of these findings, I advocate for a more nuanced understanding of ecosystem regulation through a socio-ecological lens.