Small Islands, Small Ponds, Small Communities—Water Beetles and Water Boatmen in the Faroe Islands

SIMPLE SUMMARY: The Faroe Islands in the North Atlantic consist of several small islands, and numerous small freshwater ponds can be found on most of them. These ponds are inhabited by species-poor aquatic communities. Faroese ponds are thus simple systems which lend themselves well to studying diversity of water insects and their interactions with the environment, which ultimately contributes to our understanding of patterns of biodiversity. In this study, we systematically collected water beetles and water boatmen from 57 ponds on the islands Streymoy and Eysturoy to obtain information on species distributions, diversity, and community composition, as well as their relationship with habitat characteristics. We found six small species of Dytiscidae and Haliplidae (Coleoptera) and two species of Corixidae (Heteroptera). There was a higher species diversity in shallower ponds, and community composition differed according to pond size. Geographical location and isolation between ponds did not influence diversity and community composition. We thus conclude that the distribution of water beetles and water boatmen in the Faroes is explained by habitat characteristics, specifically size and depth of the pond. ABSTRACT: Water beetles of the families Dytiscidae and Haliplidae (Coleoptera) as well as water boatmen (Heteroptera: Corixidae) are well-studied groups in Northern Europe. In the Faroe Islands, their diversity is much lower than in the British Isles and Fennoscandia. Here, we first describe the communities of water beetles and water boatmen in Faroese ponds and, secondly, assess whether community compositions are driven by habitat characteristics or dispersal abilities of species. To this end, we sampled 57 ponds, ranging between <50 m(2) and >50,000 m(2). Environmental variables such as pond size, temperature, pH, and depth were measured, and distance to nearest neighboring pond was calculated as a measure of isolation. The sampling yielded 1522 individuals of eight species, with species richness of the ponds ranging between zero and six. Pond size (shoreline length) did explain differences in community composition, whereas water depth explained differences in diversity indices with lower diversity in deeper ponds. We found species-specific relations between abundance and shoreline length, e.g., H. fulvus and H. palustris being restricted to larger ponds. Lastly, water beetle and water boatmen communities in Faroese ponds are discussed in the light of island biogeography and species distributions in the North Atlantic islands.