Individual host selection decisions and population-level responses in a time- and energy-limited forager, Dendroctonus ponderosae Hopkins

My thesis explores the link between habitat selection decisions made at the individual level and the resulting population-level distributions, using a combination of field, laboratory, and theoretical studies in mountain pine beetle (MPB), Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae: Scolytinae). Settlement decisions in MPB depend on complex interactions among the size and nutritional quality of the host tree, its defensive capabilities, beetle attack densities, and beetles’ energy reserves. Limited somatic energy reserves and time available for dispersal and habitat search impose restrictions on individuals’ settlement decisions, and can have substantial effects on the resulting population distributions. I characterized the variation in individual somatic condition and timing of emergence in a field population of beetles and tested the effect of somatic condition on beetles’ habitat settlement decisions. I derived, from first principles, a dynamic state variable model of inter-stand dispersal and tree selection by individual beetles. The model and experimental results showed that considerable individual variation exists and that settlement decisions are modulated both by the beetle’s lipid reserves and tree nutritional quality. This model provided the foundation for a spatial dynamic game model of beetle attack on multiple host tree species. I examined how the predicted evolutionarily stable strategies differ for beetles utilizing different pine species, and examined the resulting population distributions on these different tree species. Finally, using beetle dispersal estimates obtained from the dynamic game model, I explored the spread of an engineered genetic control element through MPB populations and describe how such control may be effective to suppress beetle outbreaks. I discuss the utility of considering individual variation together with state- and condition-dependent behaviours in assessing population-level phenomena.