UCLA

Temperature is one of the key sources of abiotic variation that affects all communities. Mounting evidence of climate warming makes it doubly important that we understand how perturbations to organisms' typical thermal environment influence population dynamics. My research examines the effects of temperature at individual and population levels on the cowpea seed beetle, Callosobruchus maculatus. Through the integration of mathematical theory and manipulative experiments, my research seeks to address this key gap in our knowledge.

First, I characterized the temperature response of fitness and the fundamental thermal niche (FTN) of C. maculatus. I quantified the thermal reaction norms of birth, maturation, and mortality. Through measurements of genetic variation in reaction norms I determined which components of the FTN facilitate vs. constrain its evolution. I found that maturation rate exhibits the least amount of genetic variation, suggesting that it might be a limiting factor in the evolution of the FTN. Using the FTN, I predicted temperature suitability under various climate scenarios. I found that C. maculatus would extend its range with warming climate.

Next, I studied the effects of temperature and competition in adult C. maculatus. I quantified the temperature response of competition on the per capita birth and growth rates. I found that both rates decline with increase in adult density and that competition exhibits a left-skewed response to temperature. This indicates that the responses of C. maculatus populations will differ at low versus high temperature extremes, leaving populations prone to stochastic extinctions.

Finally, I studied the effects of temperature and competition on juvenile C. maculatus. I quantified the temperature responses of maturation and juvenile mortality rates as a function of larvae present in host seeds. I found that maturation rate remains constant while juvenile mortality has a positive association with larval density. Furthermore, the temperature response of intraspecific competition on juvenile mortality is left-skewed, indicating a synergistic effect of temperature and competition.

Taken together, this work represents a step forward in understanding ectotherm species’ responses under warming. The novel aspect of this research is that it addresses fundamental questions that also have applied significance in food security.