Date of Award
Spring 2023
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Ecology and Evolutionary Biology
First Advisor
Jetz, Walter
Abstract
The ecological niche is a central concept for understanding how species will respond to climate and land-use change. Although ecologists traditionally assess niches at the species level, emerging research shows that niche variation below the species level, for example, among individuals and populations, affects many ecological processes, such as population growth rates, community assembly, and ecosystem dynamics. Thus, niche variation may be integral to accurately forecasting biodiversity responses to global change. However, it is largely unknown whether individuals vary in their environmental niches (i.e., niches with axes for environmental conditions such as habitat or land cover) or whether this variation is present across broad geographic areas. Climate and land use change directly impact conditions underlying environmental niches, so understanding environmental niche variation may be critical for predicting how populations will respond to these changes. This dissertation investigates the prevalence and form of individual and population environmental niche variation across continental scales and assesses factors affecting the breadth of environmental conditions individuals and populations use. To assess niche variation, I use movements of 726 GPS-tracked white storks (Ciconia ciconia) from populations across the latitudinal extent of the species' breeding range. To manage over 58 million movement locations, I built an integrated informatics system (called ‘mosey’) that interoperates with Movebank and Google Earth Engine to associate movements to remotely sensed environmental conditions at fine spatio-temporal grains. Using a recently developed method, I represent niches as hypervolumes, which allows the assessment of niche geometric relationships, including specialization and configuration. Chapters one and two show that individual environmental niches are highly specialized–i.e., individual environmental use is a subset of the population’s. I propose a framework based on niche breadth and overlap that moves beyond describing specialization to resolving niche geometric configuration. The results consistently show that individual niches within populations have a nested configuration (i.e., larger niches encompass smaller niches), a pattern that repeats for population niches across the species range. These results suggest that all storks have similar core environmental requirements and that niche variation arises because individuals differ in their niche breadths. Chapter three extends theory on dietary niche variation and classic models of animals foraging on patchy landscapes to propose two hypotheses for landscape-scale drivers of niche breadth. The results support both hypotheses: (1) higher landscape productivity decreases individual niche breadth, and (2) greater habitat heterogeneity increases it. In addition, this chapter presents a unique time series of fine-grained density estimates to assess how conspecific density mediates the effect of these landscape-scale drivers. This analysis indicates that population density mediated the effect of productivity and habitat heterogeneity on niche breadth. This result is potentially due to emergent social behavior at high population densities, suggesting that niche models may need to account for population density or social behavior to capture environmental relationships. Chapter four addresses conceptual challenges in individual ecology. Building upon recent literature, I developed an individual niche definition based on the organism's life cycle. Next, I propose a framework around this definition that unites isolated subfields, including home range estimation, habitat selection, animal personality, and individual specialization. In conclusion, niches assessed below the species level promise a more mechanistic pathway for understanding how individual environmental requirements shape responses to habitat loss, underlie climate-induced range shifts, or describe how species will be asymmetrically affected across their range. This dissertation provides evidence that individuals vary in their environmental niches and describes the geometric form of this variation. It identifies drivers of the breadth of individual and population environmental use and advances a conceptual individual niche definition and unifying framework that suggests synergistic benefits among individual ecology subfields. The research in this dissertation will advance an individual-based agenda for understanding, monitoring, and conserving biodiversity in the face of unprecedented environmental change.
Recommended Citation
Carlson, Ben S., "The Individual Environmental Niche: Drivers, Specialization, and Geometric Configuration" (2023). Yale Graduate School of Arts and Sciences Dissertations. 1303.
https://elischolar.library.yale.edu/gsas_dissertations/1303
