Sweep Samples of Tropical Foliage Insects: Effects of Seasons, Vegetation Types, Elevation, Time of Day, and Insularity

Abstract

Detailed data (numbers of species, numbers of individuals, measures of species diversity, evenness, dry weight) are presented on the adult beetles, adult bugs, or all arthropods, in sweep samples from Costa Rican secondary vegetation and primary forest understory during night and day, over a 3,340—m elevational transect, during the wet and dry seasons, and from Caribbean Island secondary vegetation. Adult bugs were found to be reduced much more severely than adult beetles in moving from secondary vegetation to primary forest understory. The number of species and individuals of insects is severely reduced in this transition, though the reduction in number of species is probably an artifact of inadequate samples from the forest understory. There is a strong movement of insects into moist refugia during the dry season, and a strong reduction in numbers of species and individuals during the dry season in areas with a severe dry season. In areas with a very mild dry season, the numbers and species of insects appear to rise during the dry season. There is very low overlap in insect species composition between secondary vegetation and the adjacent forest understory. The numbers of insects and species above intermediate elevations show a general decrease, and intermediate elevations appear to have the highest insect density. This is believed due to a higher harvestable productivity from the plant community at intermediate elevations owing to lowered plant maintenance costs on cool nights.The insect community changes little from day to night, except during the dry season in areas that have a severe dry season. Here there is a dramatic increase in individuals and numbers of species at night, in dry sites with nearby moist refugia. It appears that a high proportion of the insect community passes the dry season as active adults in reproductive diapause. The islands have dramatically reduced numbers of individuals as well as species of insects in both the wet and dry seasons. Part of the large insectivorous lizard community supported by these depauperate islands may be due to the lizards turning vegetarian. In order to digest vegetable matter, lizards probably have to bask in the sun; this exposes them to predators, but lizard predators are absent from the islands.