METAPOPULATIONS OF MOTHS ON ISLANDS - A TEST OF 2 CONTRASTING MODELS

1. We describe a generalized mainland-island metapopulation model whic h includes migration among the island populations. We test model predi ctions with quantitative data on more than 200 species of moths in two contrasting networks of small islands. The data include a direct meas ure of migration rate, based on trapping of moths on rocky skerries wi th no local populations of the vast majority of species. 2. We predict ed that moths which are strong fliers but uncommon on the islands have a higher incidence on scattered islands than on islands in a group, b ecause the latter 'compete' for immigrants from the mainland. In contr ast, we predicted that weakly flying species with potentially large lo cal populations on the islands occur more frequently on islands in a g roup due to enhanced colonization rate. 3. Both predicted patterns wer e observed. Island occupancy increased significantly with the number o f individuals caught on the rocky skerries, which is our measure of mi gration rate from the mainland, supporting the basic assumption that t he species occur on the islands in a balance between colonizations and extinctions. 4. These results demonstrate that the moth metapopulatio ns on islands represent a mixture of Levins's and mainland-island meta populations, and that the mixture is different for different species i n the same landscape.