The effect of resource depletion on the thermal response of mosquito population fitness

Abstract

1. A population′s maximal growth rate (rm) depends on the survivorship, development, and reproduction of its individuals. In ectotherms, these (functional) traits respond predictably to temperature, which provides a basis for predicting how climatic warming could affect natural populations, including disease vectors and the diseases they transmit. 2. Such predictions generally arise from mathematical models that incorporate the temperature–dependence of traits (thermal performance curves) measured under laboratory conditions. Therefore, the accuracy of these predictions depends on the relevance of lab-measured trait thermal performance curves to natural conditions. However, the joint effect of temperature and resource availability—another key limiting environmental factor in nature—on traits is largely unknown. 3. We investigated how larval competition for ecologically–realistic depleting resources affects the thermal performance of rm and its underlying life history traits in the disease vector in Aedes aegypti. We show that competition at food concentrations below a certain threshold drastically depresses rm across the entire temperature range, causes it to peak at a lower temperature, and narrows the breadth of temperatures over which rm is positive (the thermal niche breath). 4. This resource-dependence of the thermal performance curve of rm is driven primarily by the fact that competition delays development and increases juvenile mortality. This is compounded by reduced size at maturity, which in turn decreases adult lifespan and fecundity. 5. These results show that intensified larval competition in depleting resource environments can significantly affect the temperature–dependence of rm by modulating the thermal responses of underlying traits in a predictable way. This has important implications for forecasting the effects of climate change on population dynamics in the field of not just disease vectors, but holometabolous insects in general.