Spatial distribution of insect guilds in a tropical montane rainforest : effects of canopy structure and numerically dominant ants.

Abstract

Insect guild abundance and species richness responses to numerically dominant ant species, seasonality, and canopy structure were analysed in a successional montane tropical rainforest. Samples were taken in wet and dry seasons at three sites that had been subject to different past land use (low, intermediate, and high disturbance) and have been protected since 1967. We took two habitat scales (isolated tree crowns and canopy segments) and three categories for numerically dominant ants (presence of only one, or more than one species, or absence of dominant ant). Our results show that the larger the crown is, the bigger the chance to find herbivores is. Total insect species abundance, sap-sucking species richness, and prey abundance were higher in the low disturbance site, where the largest crowns were found, but simpler canopies showed the greatest frequency of dominant ants, and the lowest abundance of chewing insects. Sap-sucking species were more abundant in the low disturbance site, but mostly on crowns with dominant ant species. Dominant ant abundance was higher, and leaf-chewer species abundance was lower, in the high disturbance site. At the canopy scale, sap-sucking and prey species abundance and richness were higher in the low disturbance site, where canopy heterogeneity was the greatest, whereas leaf-chewers did not respond to disturbance at all. Sap-sucking species abundance was higher in areas with a simple ant species dominance. This is the first work to show how canopy insects are concomitantly affected by numerically dominant ants and canopy structure in this Atlantic rainforest ecosystem.