To tree or not to tree: The role of energy limitation on host tree acceptance in a bark beetle


Background: Energy and time constraints experienced by dispersing animals often limit individual dispersal and subsequent habitat selection decisions. When substantial variation in individual dispersal capability is present, these constraints may have significant impacts on populations where condition-dependent evaluation of habitat sites interacts with state-dependent habitat selection. Latty and Reid (2010) hypothesize that internal state of the dispersers and characteristics of their habitat mediate habitat selection (‘condition matching’). Hypothesis: Individual beetles in better energetic condition are more likely to attack better-defended trees (i.e. riskier habitat). Organism: Mountain pine beetle (Dendroctonus ponderosae Hopkins). Field sites: Two field sites were used, and work at both sites coincided with the start of the beetles’ emergence and flight period. Beetles used for lipid extraction analysis were collected near Merritt, BC, Canada in 2006, and host tree acceptance experiments were performed in 2010 near Field, BC, Canada. Methods: We sampled a population of beetles to characterize the relationship between beetle size and lipid content, then examined the variation in individual somatic energy condition and date of emergence. We separately tested the effect of somatic energetic condition on habitat (host) selection decisions by experimentally manipulating beetles’ somatic energy reserves, placing them on host trees of different nutritional qualities, and measuring the latency in beetles’ host tree acceptance. Results: Most beetles emerged early. Their somatic energy condition is higher at the start of the emergence period than near the end, although there is substantial individual variation in both timing and condition upon beetle emergence. Beetles’ host selection decisions are influenced by both host tree nutritional quality and individuals’ lipid reserves. Good nutritional quality trees are accepted sooner than poor nutritional quality trees. Individuals with lower energy reserves are less selective, accepting poorer quality host trees sooner than beetles with higher energy reserves.

Evolutionary Ecology Research