Diversity and microhabitat specificity of saproxylic beetles in a Costa Rican rainforest

Tropical forests play critical roles in storing atmospheric carbon, even after trees die. Senescing wood is initially colonized by primary saproxylic insects, and if they prefer different microhabitats, it could impact subsequent nutrient cycling. This exploratory study investigates the diversity and microhabitat specificity of two saproxylic feeding guilds in two beetle families (mycophagous Curculionidae, xylophagous Curculionidae, and xylophagous Cerambycidae). Beetles were reared from 41 trees in nine species, with bait branches exposed at canopy and ground stratum, in a mosaic of old-growth and secondary forest on the Osa Peninsula, Costa Rica. iNext was used to estimate sample coverage and diversity. Network analyses revealed the interactions of species with host plant, stratum, and forest successional stage. Specialization indices are presented for individual beetle species, and overall network selectivity. The bait branches yielded 12,310 individuals in 140 species. Both xylophagous groups were more diverse than the mycophagous curculionids. Although mycophagous curculionids collectively emerged from fewer host species, the two xylophagous groups had higher host plant specialization values. There was a tendency for curculionids to be more influenced by stratum than cerambycids, with xylophagous curculionids unexpectedly abundant in the canopy. Forest successional stage did not appear to be an important driver of community structure. Primary saproxylic beetles depend on dead wood that is patchily distributed in space and time, and this patchiness is increased by host selectivity. They are therefore vulnerable to forest loss, and modifications in community structure could affect forest nutrient cycling.