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On the brink: predicting population collapse in seasonal environments

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Title: On the brink: predicting population collapse in seasonal environments
Author: Burant, Joseph Benjamin
Department: Department of Integrative Biology
Program: Integrative Biology
Advisor: Norris, D. Ryan
Abstract: Efforts to conserve threatened species are often limited by a lack of information, including knowledge about when and where within the annual cycle threats to population persistence occur. Understanding how the timing of environmental stressors influences population dynamics is a key challenge in the conservation of species threatened by global change. Recent evidence has demonstrated how conditions in part of the annual cycle can scale up to influence the overall dynamics of seasonal populations and, ultimately, how population declines can be attributed to these season-specific effects. Despite this, it remains unclear whether these season-specific drivers of decline can be detected in times series of population abundance. In this thesis, I combine experimental and theoretical approaches, to investigate how season-specific habitat loss influences the dynamics, detection, and predictability of population collapse. In the first chapter, I used a long-term, multi-generation habitat loss experiment in populations of fruit flies (Drosophila melanogaster) with distinct breeding and non-breeding periods to investigate how season-specific habitat loss influences patterns of population collapse and changes in seasonal vital rates (reproduction and survival). This revealed that populations losing breeding versus non-breeding habitat decline in fundamentally different ways, and that the season of habitat loss can be determined using these simple demographic rates. In the second chapter, I extended a bi-seasonal Ricker model to evaluate whether season-specific signals of decline occur under a broader range of demographic conditions and rates of habitat loss. I showed that, when non-breeding habitat was lost, the strength of density dependence negatively affected time to extinction, but not when breeding habitat was lost. In the third chapter, I combined abundance time series with measurements of fitness-related traits to explore how the timing of habitat loss influenced the production of early warning indicators preceding population collapse. My analysis showed that, relative to breeding habitat loss, the predictive capacity of these indicators was greatly reduced when non-breeding habitat was lost. Collectively, my thesis research contributes to our broader understanding of where and when populations are driven to decline, and identifies simple tools aimed at addressing limitations to their conservation.
Date: 2020-12
Rights: Attribution-NonCommercial-NoDerivatives 4.0 International
Related Publications: Burant, J.B., Betini, G.S., and Norris, D.R. (2019). Simple signals indicate which period of the annual cycle drives declines in seasonal populations. Ecology Letters, 22: 2141-21150. DOI: 10.1111/ele.13393.

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