Moving forward in circles: challenges and opportunities in modelling population cycles

Population cycling is a widespread phenomenon, observed across a multitude of taxa in both laboratory and natural conditions. Historically, the theory associated with population cycles was tightly linked to pairwise consumer–resource interactions and studied via deterministic models, but current empirical and theoretical research reveals a much richer basis for ecological cycles. Stochasticity and seasonality can modulate or create cyclic behaviour in non-intuitive ways, the high-dimensionality in ecological systems can profoundly influence cycling, and so can demographic structure and eco-evolutionary dynamics. An inclusive theory for population cycles, ranging from ecosystem-level to demographic modelling, grounded in observational or experimental data, is therefore necessary to better understand observed cyclical patterns. In turn, by gaining better insight into the drivers of population cycles, we can begin to understand the causes of cycle gain and loss, how biodiversity interacts with population cycling, and how to effectively manage wildly fluctuating populations, all of which are growing domains of ecological research

Evolution of swarming behavior is shaped by how predators attack

Animal grouping behaviors have been widely studied due to their implications for understanding social intelligence, collective cognition, and potential applications in engineering, artificial intelligence, and robotics. An important biological aspect of these studies is discerning which selection pressures favor the evolution of grouping behavior. In the past decade, researchers have begun using evolutionary computation to study the evolutionary effects of these selection pressures in predator-prey models. The selfish herd hypothesis states that concentrated groups arise because prey selfishly attempt to place their conspecifics between themselves and the predator, thus causing an endless cycle of movement toward the center of the group. Using an evolutionary model of a predator-prey system, we show that how predators attack is critical to the evolution of the selfish herd. Following this discovery, we show that density-dependent predation provides an abstraction of Hamilton's original formulation of ``domains of danger.'' Finally, we verify that density-dependent predation provides a sufficient selective advantage for prey to evolve the selfish herd in response to predation by coevolving predators. Thus, our work corroborates Hamilton's selfish herd hypothesis in a digital evolutionary model, refines the assumptions of the selfish herd hypothesis, and generalizes the domain of danger concept to density-dependent predation.Comment: 25 pages, 11 figures, 5 tables, including 2 Supplementary Figures. Version to appear in "Artificial Life

An Examination of the Effects of Prey Density, Mortality, Nutrients, and Foraging Tradeoffs on a System With Inducible Defenses: An Empirical and Theoretical Approach

To grasp the functioning and stability of ecosystems, it is important to understand species interactions. With many ecosystems becoming more imperiled from urbanization and anthropogenic influences it is important to understand ways in which species can adapt to rapid changes in their environment. Phenotypic plasticity is one such tool at nature’s disposal to initiate rapid change, where species with the same genetic makeup can have different expressed traits depending on their environment. Inducible defenses are one such form of phenotypic plasticity in which prey can express different levels and forms of defense depending on the threat of predation present in their environment. In this thesis, I work to determine the mechanisms by which P. aurelia balance the costs and benefits of producing defenses through the manipulation of predator and prey densities to encourage a better understanding of this form of phenotypic plasticity. Using an experimental framework, I show that prey density leads to a reduction in base morphology but may be linked to increased defense induction in this protist. At the top of the food chain predators are important in controlling prey density and increasing mortality of predators can reduce the constraints on prey growth leading to a cascading effect through a food chain. However, adaptable prey responses to predation can lead to counterintuitive reactions of the trophic levels to predator mortality. Furthermore, the death of predators plays a key role in the cycling of nutrients in a system. Energy flows up the trophic levels of a food chain through consumption, but recycling of dead biomass and excretion allows for some of those resources to be reclaimed by the lowest trophic level. In this thesis, I also investigate inducible defenses in a theoretical setting to better understand how adaptable traits may interact with nutrient recycling and foraging costs to influence responses to predator mortality and system stability. I found that nutrient recycling led to an increased negative response of predators to their own mortality while also providing an observable increase to predator density due to bottom-up. Overall, I further our understanding of inducible defenses in natural and theoretical settings