Interspecific relations in forest floor coleopteron assemblages: Niche overlap and guild structure

Summary In six different environments of the Towada-Hachimantai National Park, the forest floor coleopterons were sampled by means of pitfall traps with five different baits. Their niche breadths and niche overlaps were assessed for the electivity of habitat, bait, and habitat × bait, and compared with those expected from neutral models constructed randomly. The niche breadths in the observed assemblages were smaller than those expected from the neutral model, while the niche overlaps were more widely distributed than those expected from the neutral model. Mean overlaps between species neighbors in niche space, cluster analyses, and ordinations of species revealed a guild for habitat, bait and habitat × bait. Lawlor’s (1979) gamma matrices concerning the habitat electivity show that the rates of mutualism resulted from indirect interspecific competitions are significantly smaller in the guild than in the whole assemblage. This suggests that the interspecific competition among the guild members is mitigated or even converted into mutualism by joining of the species which do not belong to the guild. The rates of mutualism were also significantly larger in the resource state of two dimensions (habitat × bait) than in that of either one. Therefore, if niche overlaps are measured on the basis of resource state of multi-dimensions, the rates of mutualism may increase further.