Bird taxonomic and functional diversity, group- and species-level effects on a gradient of weevil-caused damage in eucalypt plantations

Abstract

The relative contribution of bird communities to insect pest control has been seldom estimated using trait-based functional diversity indices, in opposition to the general usage of taxonomic indices simply based on the presence and abundance of species. Moreover, few studies attempted to quantify the explicit contribution of functional groups or species of birds to the control of insect pests. We investigated eucalypt plantations under a gradient of defoliation caused by the eucalyptus weevil Gonipterus platensis to assess how avian insectivory links with (1) taxonomic and (2) functional diversity indices, and with (3) groups and (4) species of functional insectivores. In agreement with our hypothesis, weevil-caused damage was negatively correlated to avian insectivory in the four studied approaches. Taxonomic diversity indices consistently presented a negative correlation with weevil-caused damage, but, contrary to our expectation, functional diversity indices were defective predictors of weevil-caused damage in eucalypt stands. Results were further explicit in the analyses conducted with groups and species of functional insectivores, wherein significant lower levels of weevil-caused damage in eucalypt stands were mainly associated with the higher abundance of canopy foragers, even though ground- and understory-gleaning species also provided competitive models at the species-level. This study establishes the importance of using multivariate trait-based approaches to understand how functional diversity drives ecosystem services, as it is here demonstrated for avian insectivory in eucalypt plantations. Top-down trophic control of the eucalyptus weevil by birds can reduce damage in areas where functional insectivorous birds aggregate.