Colonization of Islands by Carnivorous and Herbivorous Heteroptera and Coleoptera: Effects of Island Area, Plant Species Richness, and 'Extinction' Rates

Abstract

Heteroptera appear to have been more successful than Coleoptera as colonizers of the Canary and Galapagos Islands. Carnivorous and herbivorous Heteroptera on four Mediterranean islands, the Madeira-Canary Islands, the Galapagos Islands, and the California Channel Islands occur in proportions similar to those on the nearby main- land. This differs from the pattern in Coleoptera, in which carnivores are generally superior to herbivores as island colonizers. Species richness of carnivorous Heteroptera, unlike that of Coleoptera and herbivorous Heteroptera, is significantly correlated with island area in the Canary Islands. Species richness of heteropteran herbivores in- creases more rapidly with plant species richness in the Ca- naries than is so for Coleoptera. It is hypothesized that phytophagous Heteroptera are less vulnerable than Coleop- tera to the chemical defences of plants and more disposed to become facultative predators. Consequently, differences in dietary specialization, and thus colonizing ability, between herbivores and carnivores may be less pronounced in Heter- optera than in Coleoptera. The prediction that carnivorous Coleoptera, by virtue of their polyphagy, are less liable than herbivores to extinction is tested by comparing collections made 100 years apart. It is supported on Madeira, but not no Porto Santo where fewer species occur. Recapture rates are ambiguously related to extinction, however, and it is likely that forest destruction by man has accelerated species loss, especially of phytophagous species.