The effects of forest fragmentation on web spider communities in urban areas

Spiders are generalist arthropod predators living in all kinds of forests. Since food limitation appears to be widespread, this group may be influenced by forest fragmentation in various ways. We examined web spider communities in one continuous forest and 17 forest fragments surrounded by built-up areas in Yokohama and Tokyo, Japan. Smaller fragments had fewer species and lower density of individuals. For a given size fragment, those in Yokohama harbored more species than those in Tokyo, probably due to the lower degree of isolation from surrounding fragments in Yokohama. Large araneids were most sensitive to fragmentation in the sense of species loss, small araneids intermediate, and theridiids least sensitive. The body size of Nephila clavata, a common species in fragments, was smaller in smaller fragments. We propose that one important mechanism of species loss in web spiders is the lower abundance of large prey in small fragments. (C) 1998 Elsevier Science Ltd. All rights reserved.