The influence of treefall gaps on the distribution of web-building and ground hunter spiders in an Atlantic Forest remnant, northeastern Brazil

In tropical forests, treefall gaps differ in several environmental parameters from the adjacent mature forest. These differences affect vegetation structure and composition that, in turn, influence the distribution of animal species. This paper compares assemblages of two groups of spiders (web builders and ground hunters) found in mature forests and treefall gaps in an Atlantic Forest remnant near Recife, Brazil. Spiders were sampled monthly by using pitfall traps and hand-searching (looking up and looking down) methods from June to November 2000. A total of 529 adult individuals distributed among 57 species were captured in pitfall traps whereas a total of 1467 individuals distributed among 117 species were captured by using the hand-searching method. The number of individuals and species did not differ between mature forest and treefall gaps in both sampling methods. More exclusive species were found in mature forest than in treefall gaps in hand-searching samples whereas an opposite result was found in pitfall samples. Habitat preferences were evaluated for those species represented by more than six specimens. Habitat preferences were significantly more marked among species sampled by hand-searching than by pitfall traps. The mosaic formed by mature forest and treefall gaps seems to influence the distribution of spider species within areas covered by tropical forests, but this conclusion should be evaluated more carefully in other tropical forest sites and by using a more diversified set of sampling procedures.