Stream insects and gastropods in the island of Gran Canaria (Spain)

The current status of the stream-living insects and gastropods of the islan d of Gran Canaria in the Atlantic Canary Islands is documented. Data from s emiquantitative kick samples taken in 11 streams are supplemented by non-st andardized collecting in the same and ten additional streams. The kick samp les included some 9,000 specimens of 98 taxa, and in total 123 taxa were re corded from the studied streams in 1994 and 1995. The stream fauna was domi nated by Diptera with some 80 taxa, followed by Coleoptera with 37 species known from the island. The kick samples yielded 11-36 species per stream an d visit, whereas up to 48 species were scored when all collecting methods w ere included. Local diversity given as Fisher's alpha ranged from 3.2 to 10 .3. Clustering showed only weak spatial patterns and resulted in much highe r similarities among localities when based on the semiquantitative samples than when based on presence/absence including records from all collecting m ethods. Species distributions among localities were not significantly neste d. The faunal similarity with the adjacent island of Tenerife is striking. Six of the Tenerife species are seemingly absent from Gran Canaria, whereas Gran Canaria has 13 species not found in Tenerife. Most of the 22 aquatic insect species in Gran Canaria only known from older records, prefer lentic habitats not included in our study. All except one of the five species end emic to Gran Canaria are considered extinct or on the edge of extinction. I ncreased future extinction rates are predicted as a response of the extreme habitat loss, with only three permanent streams known on the island today.