Altered trophic interactions in a warming environment: insights into the population dynamics of eruptive herbivores

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Although the direct and indirect influences of climate change on herbivorous insects are expected to be variable and complex, the most commonly documented result of warming to date has been shifts in their distribution. Elucidation of altered trophic interactions associated with distributional changes and habitat invasion by an alien insect herbivore can provide important insights into fundamental ecological processes. For species prone to dramatic population fluctuations and widespread outbreaks, comparisons of trophic interactions in novel and native habitats make it possible to identify key factors influencing their population dynamics, and quantify the selective pressures shaping their evolution.      As a consequence of a warming environment the mountain pine beetle (Coleoptera: Curculionidae: Scolytinae) has undergone a dramatic range expansion into regions dominated by novel host populations and species. Using this insect herbivore as a model system, the proposed research seeks to quantify the trophic interactions and population dynamics of an eruptive forest insect in native versus recently invaded forests. More specifically, comparative studies will quantify the relative contribution of (i) host-tree defenses, (ii) interspecific competitive interactions, and (iii) interactions with natural enemies to the generation mortality and dynamics of mountain pine beetle in native lodgepole pine (Pinus contorta var. latifolia) habitats versus newly colonized, and putatively evolutionarily naïve, lodgepole pine, jack pine (Pinus banksiana) and lodgepole x jack pine hybrid habitats.      The recent range expansion by the mountain pine beetle comprises the first example in North America of significant habitat invasion by an indigenous eruptive herbivore. Using 6 interrelated research projects that will enable the training of 3 PhD and 3 MSc candidates, and up to 24 undergraduates (2 BSc theses, 12 field assistants, 10 lab assistants), this research will provide critical insights into the dynamics of herbivorous insect populations, the evolution of insect-plant interactions, and the processes of habitat invasion by eruptive species.