Microhabitats increase the niches available to saproxylic beetles, potentially impacting nutrient recycling in senescing wood. In Neotropical rainforests, preferences are poorly known. This rearing study explores the abundance, richness, and network structure of primary saproxylic beetles. The study site was on the Osa Peninsula of Costa Rica, in a mosaic of old growth and secondary lowland rainforest. The focal beetle groups were mycophagous Curculionidae (ambrosia beetles), xylophagous Curculionidae (bark beetles and snout weevils), and Cerambycidae. Bait branches were cut from 40 trees (in eight plant species) near the beginning of the rainy season, and exposed at ground and canopy stratum for three months. Curculionids were expected to be moisture-dependent and preferentially associated with ground stratum, and xylophagous beetles were expected to be more host specific. Mycophagous curculionids were most abundant at ground stratum, but both groups of xylophagous beetles were surprisingly abundant at canopy stratum. Mycophagous curculionids less species-rich than the other groups at both strata. In Bipartite analyses, both xylophagous curculionids and cerambycids had higher levels of host plant specialization than the mycophagous curculionids. Collectively, the mycophagous beetles occupied fewer of the available niches—they were sparse at canopy stratum, and also in five of the eight potential host species. Competition did not appear to be a major factor in determining community structure: the three groups of beetles occurred in complex assemblages within a branch, with up to 17 (canopy) or 29 (ground) co-occurring species. Interactions within a branch— potentially antagonistic or beneficial— are still poorly understood.
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