Open canopy increases the species richness of fungus weevils in Madagascar forests

Abstract

Tropical forests have high biodiversity. Nevertheless limited information is available about the species richness of fungus weevils in the family Anthribidae in disturbed and undisturbed tropical forests. Anthribids are saproxylic, i.e., they depend on dead wood.Our aim was to investigate the relationships between the species richness of anthribids and environmental and other independent variables in the equatorial tropical forests of Madagascar.We used beating and sweep nets to collect adult anthribids in 62 forest sites over three consecutive years (2015–2017). We then used generalized linear models (GLM) to determine the relationships between anthribid species richness and the following independent variables: stage of the forest; canopy openness; largest deadwood size-category; number of size-categories present; wood decay stage; the presence of a flight corridor; elevation; number of times a site was sampled; and sampling year.Among the 202 anthribid species collected, > 50% were new (not described). Species richness was positively and closely related to openness and was independent of forest stage (old-growth vs. secondary); the number of new species detected, however, was higher in old-growth forests than in secondary forests. Species richness was also positively related to the quantity and quality of deadwood.Much of anthribids biodiversity is hidden and many new species may never be discovered if old-growth forests are logged. The openings in the canopy should be created to maintain suitable habitats for the occurrence of anthribids, but this does not usually require management. Canopies with openings occur naturally in old-growth forests and are commonly created in secondary forests by cutting. Leaving branches and twigs of various should help maintain the species richness of anthribids and probably of other organisms.