Competition and Coexistence In a Multi-partner Mutualism: Interactions Between two Fungal Symbionts of the Mountain Pine Beetle In Beetle-attacked Trees |
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Authors: | K P Bleiker D L Six |
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Institution: | (1) Department of Ecosystem and Conservation Science, University of Montana, Missoula, MT 59801, USA;(2) Present address: Pacific Forestry Centre, Canadian Forest Service, 506 West Burnside Rd., Victoria, British Columbia, V8Z 1M5, Canada |
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Abstract: | Despite overlap in niches, two fungal symbionts of the mountain pine beetle (Dendroctonus ponderosae), Grosmannia clavigera and Ophiostoma montium, appear to coexist with one another and their bark beetle host in the phloem of trees. We sampled the percent of phloem colonized
by fungi four times over 1 year to investigate the nature of the interaction between these two fungi and to determine how
changing conditions in the tree (e.g., moisture) affect the interaction. Both fungi colonized phloem at similar rates; however,
G. clavigera colonized a disproportionately larger amount of phloem than O. montium considering their relative prevalence in the beetle population. High phloem moisture appeared to inhibit fungal growth shortly
after beetle attack; however, by 1 year, low phloem moisture likely inhibited fungal growth and survival. There was no inverse
relationship between the percent of phloem colonized by G. clavigera only and O. montium only, which would indicate competition between the species. However, the percent of phloem colonized by G. clavigera and O. montium together decreased after 1 year, while the percent of phloem from which no fungi were isolated increased. A reduction in
living fungi in the phloem at this time may have significant impacts on both beetles and fungi. These results indicate that
exploitation competition occurred after a year when the two fungi colonized the phloem together, but we found no evidence
of strong interference competition. Each species also maintained an exclusive area, which may promote coexistence of species
with similar resource use. |
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