Author ORCID Identifier

https://orcid.org/0009-0007-9090-3404

Semester

Summer

Date of Graduation

2026

Document Type

Thesis

Degree Type

MS

College

Davis College of Agriculture, Natural Resources and Design

Department

Wildlife and Fisheries Resources

Committee Chair

Eric Hileman

Committee Member

Lisa Faust

Committee Member

Christopher Rota

Abstract

Managing at-risk species or populations requires understanding the demographic and genetic drivers of long-term population trends. The eastern massasauga rattlesnake (Sistrurus catenatus) is a federally threatened species facing multiple interacting threats across its range. Habitat loss from wetland drainage and agricultural land conversion has caused range contractions and geographic isolation of populations. Because remaining populations are often small and widely separated, most are now genetically isolated, threatening their long-term viability. Reversing these declines requires understanding population dynamics, quantifying extinction risk, identifying drivers of long-term viability, and assessing the effects of inbreeding and the potential for genetic rescue to mitigate inbreeding-driven declines. Using data from two long-term study populations of eastern massasaugas in southwest Michigan, we applied capture-recapture models to retrospectively assess population dynamics and population viability analyses (PVA) to quantify future viability in populations known to be experiencing inbreeding depression. In chapter 1, we used a robust design, time-symmetric model on long-term capture-recapture data (2011 – 2025) on adult female eastern massasaugas to estimate apparent survival, recruitment, realized population growth, and abundance. Apparent survival varied from 0.598 – 0.776 and increased with female body size. Annual per-capita recruitment rate was constant over time, at 0.319 (95% CI = 0.270 – 0.372). Model-averaged estimates of adult female abundance ranged from 42.5 – 140.7, with a model-averaged estimate of realized population growth of 1.013 (95% CI = 0.986 – 1.040), suggesting slight positive growth over the previous 15 years. Survival of adult females accounted for 68.5% (95% CI = 63.5 – 73.3%) of the variation in realized population growth. These retrospective results reveal a stable population driven primarily by adult female survival, suggesting management should prioritize minimizing adult female loss to improve persistence. In chapter 2, we used PVA to reassess the population viability after newfound evidence of inbreeding depression. We applied population-specific measures of inbreeding load to quantify the effect of inbreeding depression on population viability and modeled alternative genetic rescue scenarios to evaluate their potential to mitigate inbreeding depression. Results indicated little risk of population extinction in either focal population; however, one population showed evidence of a genetic-demographic feedback loop driven by inbreeding. Genetic rescue simulations suggested that population augmentation can offset inbreeding effects, but translocation mortality must be minimized to make augmentation more logistically feasible. Alternatively, restoring connectivity between populations, where possible, may achieve recovery with relatively few immigrants per year. Results from this study present a nuanced view of the conservation needs of our focal populations and for the species at large. Capture-recapture modeling revealed a stable population over the past 15 years despite known inbreeding depression. Looking forward, extinction risk appears low, although demographic and genetic decline is anticipated in at least one population experiencing inbreeding depression. Collectively, the results from this study will provide valuable information for future management decisions regarding the eastern massasauga throughout its range.

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