Differences in Insect Abundance and Diversity Between Wetter and Drier Sites During a Tropical Dry Season

Abstract

During the dry season in Costa Rica, sweep samples were taken of forest understory insects in three adjacent habitats of increasing moistness (Guanacaste Province: Areas I through III) and in another habitat under a much wetter precipitation regime (Limon Province; Area IV). These samples were then compared with respect to numbers of individuals, numbers of species, size frequencies, weight, developmental stages, species diversity, trophic levels, taxonomic composition and species exclusiveness. The absolute numbers of species increased from Areas I through IV; the numbers of individuals, frequency of small insects, dry weight, individuals per species and percent parasitic species increased from Areas I through III. The several indices of species diversity calculated for the samples only show partial agreement in relative values and trends. The data clearly demonstrate that adjacent tropical communities can have greatly different insect components. The possible effects of the differences between the insect communities of Areas I to III on vertebrate predators and plants are discussed. When compared with temperate data on insect communities there are indications that the four tropical communities examined have a much greater number of species and possibly a greater internal uniqueness than similar temperature communities.