DISTRIBUTION PATTERNS OF FRESH-WATER OSTRACODA (CRUSTACEA) IN THE CANARY-ISLANDS WITH REGARDS TO HABITAT USE AND BIOGEOGRAPHY

In this study biogeographic patterns and habitat relationships of fres hwater Ostracoda were investigated in the Canary Island archipelago. M ost data were collected from published studies, though also new data f rom Gran Canaria are presented. In all, 22 freshwater species are pres ently known to the Canaries. Six species, viz. Ilyocypris bradyi, Cypr is bispinosa, C. pubera, Herpetocypris chevreuxi, Heterocypris incongr uens, and Sarscypridopsis lanzarotensis are new to Gran Canaria, the f irst two also being new to the Canaries in general. Testing the influe nce of a number of variables on faunal richness indicated only a weak association with island area. Distances between islands also proved no t significant, and so did other properties of islands, including age, altitude and precipitation. This was in contrast to a comparison set o f data comprising aquatic beetles. Like beetles, however, ostracods di d not show a nested pattern, i.e. faunas of species-poor islands were not subsets of species-rich island faunas. By having low endemicity (e ndemic species lacking in the Canaries), the, ostracod fauna resembled island fern floras. Both groups of organisms have tiny diaspores (dia meter <0.1 mm) and are extensively parthenogenetic suggesting similar dispersal and founder mechanisms. We identified a pattern (with one ex ception), where those species with distributions extending across seve ral islands also had wider within-island distributions. Many species s howed affinities to different habitats depending on conductivity of wa ter, altitude and habitat types: whether they were permanent or tempor ary, hypogean or epigean, or characterized by running or stagnant wate rs.