Spatial heterogeneity of carabid beetle dispersion in uniform forests on the Åland islands, SW Finland

Abstract

We studied the spatial occurrence of carabid beetles in four uniform forest areas on the Aland Islands, SW Finland. In each of the forest areas we took samples in five sampling sites with fifteen pitfall traps. The spatial dispersion of carabids was examined on both the community and the species level and in three spatial scales: (1) among the traps in each sampling site, (2) among the sampling sites within each forest area, and (3) among the forest areas. An ordination analysis did not reveal any systematic differences in the floristic characteristics among the sites. Within the sampling sites, Trechus secalis showed an aggregated dispersion pattern in six out of 12 sites analyzed. The two other species analyzed (Pterostichus melanarius, P. niger) both differed from random dispersion in one site. Out of the six species studied only T. secalis showed an aggregated dispersion pattern among the sites in every forest area. A one-way analysis of variance indicated that none of the abundant species had an aggregated dispersion among the forest areas. In small spatial scales, aggregated dispersion pattern of forest carabids seems to be the rule, but the pattern has no obvious explanation in habitat variability.