My research focuses on elucidating the mechanisms by which individual level variation translates into population level patterns. I ask questions about the role of intraspecific life history variation in population extinction, competitive coexistence, community assembly, and local adaptation. I use complementary mathematical and statistical approaches that are both strongly tied to natural systems, creating a unified framework that integrates population and community models with frequentist and Bayesian statistical approaches.
Phenological shifts in consumer-resource dynamics
Phenological shifts, changes in the timing of life history events, are one of the clearest manifestations of climate change. We have built a predictive framework based on mechanistic thermal responses of life history traits to ask how a population's phenological pattern of abundance may change in response to climate warming (Scranton and Amarasekare, 2017). We are currently expanding this framework to model consumer resource dynamics and predict climate change driven phenological mismatches. Preliminary results indicate that the effect of temperature on the interaction dominates the resulting dynamics, mediated by the consumer's functional response, as well as both species' maturation. Dynamics under simulated scenarios of climate change indeed show that the consumer-resource interaction erases phenological shifts that would occur if the resource were in isolation: resource biomass is converted into consumer biomass as the resource grows in the spring.
Analytically quantifying the thermal niche reveals that while survival during the developmental period strongly affects the thermal limits of feasibility, attack rate and handling time create a sharp boundary at cooler temperatures where the consumer cannot survive on the resource. Simulated dynamics confirm the importance of attack rate at cooler temperatures, as slightly maladapted consumers are restricted in their activity during very hot summers, creating shifts in consumer-resource cycles earlier in the spring. The phenological shifts reappear, here as a result of the effects of temperature on the species interaction.
Complex cycles in Host-Parasitoid dynamics
We are also developing novel statistical methods and stochastic models to investigate the role of intraspecific competition in driving observed quasi-cyclic patterns in population dynamics. We model the dynamics of a parasitoid population with a system of delay differential equations and incorporate demographic stochasticity using a Gillespie algorithm. We fit the stochastic analogue of the DDE model using an approximate Bayesian computation (ABC) framework in order to estimate the form and strength of competition. We find that exploitative competition for a supplemental resource (honey) strongly drives the overall abundance of the population through its effects on adult mortality, but interference competition for host eggs modifies resource availability. The amplitude and period of the oscillations in the dynamics are driven by the interaction of the period of resource availability and the duration of the egg and larval stages of the parasitoid.