Theodore Lee Grabarz, Ph.D., is a 2023 graduate of the Ph.D. Program in Environmental Studies at Antioch University, New England
- James Jordan, PhD, Committee Chair
- Lisabeth Willey, PhD, Committee Member
- Antonios Pappantoniou, PhD, Committee Member
habitat quality, stress response, glucocorticoids, habitat quality stress index, immune-competence, proximate fitness, American Crow
All organisms occur within spatial and temporal environments to maximize proximate fitness (health) and thus life history outcomes. Previous work has examined the temporal and behavioral aspects of proximate fitness on life history outcomes particularly regarding highly perturbed environments (i.e., climate and land use change, resource extraction, agricultural erosion, etc.). My work focuses on the less examined spatial aspect of these perturbed environments. More specifically, this dissertation examines habitat selection and quality as the basis for understanding stress response (negative and positive feedback mechanisms) to environmental stressors within the larger context of regional or gamma (ɣ) biodiversity. Through the lens of environmental endocrinology, I examine patterns of glucocorticoid (GC) hormone differentiation spatially. I do this to understand how biotic and anthropogenic environmental stressors affect stress response in the American Crow (AMCR). This stress response could have an impact on human disease origins. I examined 13 sites throughout the State of Connecticut between 2019 and 2021, from very rural to very urbanized. I collected 153 opportunistic fecal samples of AMCR, then used radio immunoassay to characterize and quantify the samples as GC hormones, a key chemical constituent that reflects stress response in avian subjects. I then used a geographic information system (GIS) to plot various catchments for each sample centroid as notional representations of AMCR territories. I then overlayed 15 landcover types as biotic and anthropogenic environmental stressors (ESs). I used ordinary least squares linear regression for my initial analyses to evaluate the degree of validity of the ES–GC relationship at discrete locations where samples were taken and subsequently within varying sized territorial catchments. Finally, I reinterpreted a single constrained gravity model for the development of a habitat quality stress index (HQSI) to understand more dynamically how stress response is affected by movement around AMCR territories. Originally based on Newton’s law of universal gravitation I believe this is the first use of such a model in evaluating stress response via fecal GCs in an ecological setting across a spatial landscape. A major takeaway from these findings is that the historically understood linearly composed landscape gradient has a much greater extracellular or episodic or granular location-specific nature. Examining GIS raster imagery for instance, yields dramatic differentiation of land cover types over very small areas (<0.1 km2) that indicates stress being applied in a highly stochastic manner. This coupled with the dramatic variation in GC levels around roost areas shows AMCR likely traveling significant distances over and through locations with various levels of environmental stressors to arrive at their roost sites each evening. Stress is mediated most effectively when there is consistency or linearity in its application, facilitating a rapid return to equilibrium. The extracellular nature of landcover examined showed a dramatic differentiation that stress response is unable to adjust toover time, without having a pathological response. This results in the extension or lengthening of the negative feedback response culminating in disequilibrium of a positive feedback response, and thereby reduction in proximate fitness and immunological resistance. AMCR, more so than many other taxa, is a highly social and adaptable avian species due to its higher level of cognition and neuroplastic nature (rapid flexibility and adaptation of response via its sophisticated central nervous system [CNS]). The AMCR populations in the roosts I observed thus favor urban locations. However, AMCR’s endocrine system adapts more slowly than their CNS (brain) to higher stress environments. Social cohesion thus outweighs homeostatic balance. In effect we would say that they are too smart for their own good!
Grabarz, T. L. (2023). The Use of a Habitat Quality Stress Index to Evaluate Stress as an Analog for Proximate Fitness in the American Crow Within a Matrix of Landcover Characteristics to Assess Its Potential Contribution to Disease Etiologies. https://aura.antioch.edu/etds/997
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