Habitat occupancy of carabid beetles on small islands and the adjacent Aland mainland, SW Finland

Abstract

The occurrence of the species over the habitats was roughly similar on the islands and on the mainland. An ordination analysis showed that the carabid assemblages tend to be more similar within islands than between them. This can probably be attributed to the movement of individuals from one habitat patch to another, which tends to even out dif ferences in species composition between patches. Due to the small size of the patches on the islands, most carabid species are able to cover the distances between neighbouring patches. Only two of the thirteen abundant species were more numerous on the islands than on the mainland. Eight species were more abundant on the mainland, and three were equally abundant on the islands and on the mainland. The island-mainland distribution patterns were similar to those found in one habitat type only in a previous study. There are no obvious explanations for these patterns, but habitat effects, differences in dispersal ability and interspecific interactions are suggested.