Dissertation

Kadowaki (2010) Wood-decaying fungi and beetles: a multi-lateral approach to studying fungus-insect communities. The University of Auckland. Download here (Open Access)

Abstract: Fungus-insect interactions permeate through the intricate tapestry of terrestrial ecosystems, but remain a persisting mystery in ecology. The wood-decaying basidiomycete Ganoderma produces perennial sporocarps (fruiting bodies) that provide food (spores) and habitat (hymenial surface) for three endemic beetles; Zearagytodes maculifer (Leiodidae) and two Holopsis species (Corylophidae) that occur in sympatry in the Waitakere Ranges, Auckland, New Zealand. Ganoderma spore release from individual sporocarps undergoes density fluctuations of two orders of magnitude that are neither clearly associated with temperature and humidity nor spatially synchronous. Such resource dynamics did not exert a strong effect on spore-feeding beetles since they use a minute percentage of spores discharged from the hymenial surface and are therefore not resource-limited. Competition at sporocarp patches is pervasive in the beetle community, as beetles range over a restricted area on the hymenial surface to feed and are likely to be space-limited. The three spore-feeding beetles display different host specificity, spore consumption patterns, dispersal behaviour, and seasonality. Remarkably, the two Holopsis species differ in their ontogenetic niches. The long rostrum of Holopsis sp. 1 gives it competitive superiority. All these factors combined to create a complex competitive network among the three species, but competitive coexistence is likely to occur as Z. maculifer and Holopsis sp. 2 evade competition with Holopsis sp. 1 via different colonisation strategies across sporocarp patches. There was no evidence for a fungus-insect mutualism: Z. maculifer does not disperse Ganoderma spores as passage through the beetle gut destroyed the spores and virtually none germinated. Altogether, the unique lifestyles of spore-feeding beetles ―living on the surface in long-lasting, exposed habitats dictate much of this tiny but extraordinary ecosystem of the fungus-insect community, characterized by the structuring forces of weak fungus-insect interactions and strong insect competition.

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