Effects of Natural Forest Fragmentation on a Hawaiian Spider Community

Thekipuka system, anetworkof forest fragments surroundedby lavaßowson the island of Hawaii, offers an opportunity to study the natural, long-term fragmentation of a native ecosystem. We examined the impacts of habitat edges upon the community structure of nocturnally active native spiders, primarily in the genus Tetragnatha.Wemeasured plant and spider species distributions across the edges of four small fragments and one large continuously forested area that were surrounded by a lava ßow in 1855. Results indicated that an 20m edge ecotone surrounds core forest habitat. Spider community structure changed across the edge, with a decrease in total species richness and diversity at the forest/lava boundary, and a change in the dominant taxon from native Tetragnatha (Tetragnathidae) to native Cyclosa (Araneidae). Severe habitat restrictions were found for some spider species. In addition, nearly all of the spiders captured were endemic species, and the few introduced species were limited to the younger and more open lava ßows. Our results suggest that species responses to edges can vary, and that core habitat specialists may decline in fragmented conditions.