Date of Graduation

5-2023

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Biology (PhD)

Degree Level

Graduate

Department

Biological Sciences

Advisor/Mentor

Adam Siepielski

Committee Member

Andrew J Alverson

Second Committee Member

Samuel B Fey

Third Committee Member

J.D. Willson

Keywords

Anthropocene;Extreme event;Global change

Abstract

Global declines of animal abundances are emblematic of the Anthropocene. Recent animal declines have increasingly involved more frequent and intense die-offs within populations, or mass mortality events (MMEs). These extreme demographic events can lead to rapid changes in biological communities, either by imperiling the affected population or influencing populations remaining within communities. To date, there is still limited information about the effects of predator MMEs on immediate ecological dynamics within communities and rapid evolutionary dynamics within remaining populations that may ensue. Moreover, few approaches exist to predict future occurrences of predator MMEs across broad spatial scales. To address these gaps, I conducted two experiments to understand how predator MMEs affect (1) tri-trophic freshwater food web dynamics, and (2) rapid adaptive evolution of consumer life history traits. Lastly, I compiled one of most comprehensive datasets of freshwater fish MMEs (3) to predict their future frequency under a warmer climate. In Chapter 1, I conducted a freshwater mesocosm experiment to understand how community dynamics were affected by two key features of predator MMEs: weakened top-down effects following the death of predators (i.e., removing predators), and a strengthened bottom-up (i.e., resource) effects via the decomposition of predator carrion. Predator MMEs led to trophic biomass responses that were best predicted by the additive effect of removing predators and adding predator carrion, as well as distinct zooplankton and, to a lesser extent, microalgae biomass dynamics compared to similar perturbations. In Chapter 2, I conducted a rapid evolution experiment to understand how two main biotic drivers that could be change in strength following the loss of fish predators affect consumer population dynamics and life history trait evolution. Specifically, some fish predators are known to exert strong selective pressures on consumer body size (size-selective predation) and other key life history traits, whereas contrasting resource levels can lead to divergent life history changes and generate opposing effects on population dynamics (e.g., increase or population density). Resource level drove population dynamics, predation type had the greatest impact on rapid adaptive evolution of life history traits, but there was only evidence for feedback between rapid trait evolution and concurrent population dynamics under size-selective predation and low resource levels. In Chapter 3, I compiled the most comprehensive databases of freshwater fish mortalities and concurrent temperature estimates across North American north temperate lakes. I then used future water and air temperature projections across lakes to predict the annual frequency of fish MMEs related to warm temperature over the 21st century. Collectively, these studies improve our basic understanding about the immediate effects of rapid predator losses on ecological dynamics within communities and evolutionary dynamics within consumer populations, as well as help establish baseline predictions of their future frequency in an increasingly volatile world.

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