UBC Theses and Dissertations
Novel biological interactions influence the persistence potential of invasive mountain pine beetle (Dendroctonus ponderosae) in the Canadian Boreal Forest Pokorny, Stanley Wolf
Favorable climatic conditions at historical range boundaries have allowed several insect species with eruptive population dynamics to invade adjacent habitats, sometimes causing severe impacts on forest health. However, the potential for recurrent outbreaks in novel habitats is uncertain because the reproductive fitness exhibited during outbreaks is temporary. Persistence in recently invaded habitats depends on the ability of the invasive species to persist at sub-outbreak or endemic population densities. I investigated the potential for mountain pine beetle (Dendroctonus ponderosae) to persist in its expanded outbreak range by quantifying interactions that are critical for survival of endemic populations. In lodgepole pine (Pinus contorta var. latifolia), epidemic-phase mountain pine beetles (hereafter ‘epidemic-phase beetles’) attack vigorous trees and endemic populations (hereafter ‘endemic-phase beetles’) preferentially colonize moribund trees. Although endemic- phase beetles exhibited this behavior in both habitats, the endemic niche in lodgepole pine was much more suitable than in jack pine (Pinus banksiana) habitats. Endemic susceptible trees were scarce in jack pine as compared to lodgepole pine stands (1-5/ha vs 6-13/ha, respectively), and susceptible host abundance was correlated with stand density index (SDI), a measure of inter-tree competition. Endemic susceptible jack pines were commonly occupied by woodboring beetles (Cerambycidae and Buprestidae), 25-60% of trees in a stand, and dissected bolts harvested from such trees exhibited high phloem consumption, mean = 58%, compared to trees occupied solely by secondary bark beetles, mean = 3%. I further showed that woodborer larvae attracted woodpeckers to forage on endemic susceptible trees, suggesting that woodpeckers in invaded habitats may have stronger impacts on the survival of endemic-phase beetles compared to the native range. I show that: 1) mountain pine beetles can differentiate between vigorous and defensively compromised trees in lodgepole and jack pine stands, 2) jack pine habitats are resource poor and have elevated competition for phloem compared to lodgepole pine habitats, and 3) niche overlap with woodborers in jack pine increases the risk of mortality by woodpeckers adapted to exploiting woodborers as food. Due to the reduced endemic niche, post-epidemic populations are unlikely to persist in sufficient densities to facilitate future eruptions in western boreal jack pine forests.
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