Species coexistence patterns in a mycophagous insect community inhabiting the wood-decaying bracket fungus Cryptoporus volvatus (Polyporaceae: Basidiomycota)

Kohmei Kadowaki

doi:10.14411/eje.2010.012

Abstract

A study of the insect community inhabiting the wood-decaying bracket fungus, Cryptoporus volvatus was used to test two hypotheses proposed to account for the competitive coexistence of species in insect communities in patchy environments, niche par- titioning and spatial mechanisms. A total of 8990 individuals belonging to 17 insect species emerged from 438 sporocarps (patches) collected from the field. Insect species richness increased and then declined with increase in the total insect biomass reared from a sporocarp, suggesting the potential importance of interspecific competition. Successional niche partitioning explained the spatial dis- tribution of the four specialist species. The aggregation model of coexistence satisfactorily explained the stable coexistence of the species. The specialist species displayed higher population persistence than the generalists. Simulation studies suggest that restricted movements of adults could override patch-level larval aggregation. The effect of such restricted movements on stabilizing coexis- tence in fungus-insect communities has not been previously appreciated. These findings suggest that spatial mechanisms play a cru- cial role in the competitive coexistence of the species in the mycophagous insect communities inhabiting bracket fungi.

Highlights

Considerable effort has gone into studying the mechanisms underlying competitive coexistence in insect communities in patchy environments (Shorrocks et al, 1979; Ives, 1991; Toda et al, 1999; Wertheim et al, 2000; Takahashi et al, 2005b)
The spatial mechanisms hypothesis posits that when different species are spatially aggregated in a number of patches, this can by chance create spatial refuges for inferior competitors
The wood-decaying annual polypore Cryptoporus volvatus (Peck) Shear (Polyporaceae: Basidiomycota) in temperate forests in central Japan is inhabited by a species-rich insect community (Sestuda, 1993, 1995)

Summary

Introduction

Considerable effort has gone into studying the mechanisms underlying competitive coexistence in insect communities in patchy environments (Shorrocks et al, 1979; Ives, 1991; Toda et al, 1999; Wertheim et al, 2000; Takahashi et al, 2005b). The niche partitioning hypothesis posits that different insect species use different resources (resource partitioning, sensu Wertheim et al, 2000), or different developmental and/or life stages of a resource (successional niche partitioning; Guevara et al, 2000; Jonsell & Nordlander, 2004; etc.), or different organs and/or parts of a given resource (Matthewman & Pielou, 1971; Hackman & Meinander, 1979). The spatial mechanisms hypothesis posits that when different species are spatially aggregated in a number of patches (e.g., fungus-dwelling insects in individual sporocarps), this can by chance create spatial refuges for inferior competitors (the so-called aggregation model of coexistence; Atkinson & Shorrocks, 1981; Ives & May, 1985). The movements of insects are restricted at the scale of “clumps of patches” (hereafter superpatches), thereby increasing the number of patchlevel spatial refuges for inferior competitors (Inouye, 1999)

Methods

Results

Conclusion