Antagonism between the fungal symbionts of bark beetles may represent a biologically significant interaction when multiple beetle species co-occur in a host tree. Since high density bark beetle populations rapidly and dramatically shift forest characteristics, patterns of competition between the obligate fungal associates of sympatric bark beetle species may have broad ecological effects. Primary and competitive resource acquisition between allopatric and sympatric isolates of mutualist fungi associated with the bark beetles Dendroctonus frontalis andDendroctonus brevicomis were investigated. Growth assays at multiple temperatures suggest that primary resource acquisition by fungi growing in the absence of competitors varies regionally, and that optimal growth rate is likely to correspond to average summertime maximum temperatures. In competition assays, interactions were asymmetric between fungi isolated from sympatric beetle populations and fungi isolated from allopatric beetle populations: sympatric isolates out-competed allopatric isolates. However, competition between fungi from beetle populations in sympatry was found to be equal. These studies are the first to investigate interactions between the mycangial fungi of multipleDendroctonus species, and the results suggest that competition is likely to occur when the mycangial fungi of multiple beetle species occur together.
Key words: Allopatric, competition, coexistence, mutualism, mutualist, mycangial fungi, sympatric.
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