Evol Ecol Res 16: 337-349 (2014)     Full PDF if your library subscribes.

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

Alex M. Chubaty1,2,3, Melanie Hart3 and Bernard D. Roitberg3

1Natural Resources Canada, Canadian Forest Service, Victoria, BC, Canada,  2Faculté de foresterie, de géographie et de géomatique, Département des sciences du bois et de la forêt, Université Laval, Québec, Canada and  3Evolutionary and Behavioural Ecology Research Group, Department of Biological Sciences, Simon Fraser University, Burnaby, BC, Canada

Correspondence: A.M. Chubaty, Natural Resources Canada, Canadian Forest Service, Pacific Forestry Centre, 506 Burnside Road W, Victoria, BC V8Z 1M5, Canada.
e-mail: achubaty@nrcan.gc.ca


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 the 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. Trees of good nutritional quality are accepted sooner than ones of poor nutritional quality. Individuals with lower energy reserves are less selective, accepting host trees of poorer quality sooner than beetles with higher energy reserves.

Keywords: dispersal, host selection, state-dependent behaviour, condition-dependent behaviour, bark beetles, Dendroctonus ponderosae.

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