Ground spider communities in experimentally disturbed Mediterranean woodland habitats

Abstract

The protected Mediterranean woodland habitats in Israel are undergoing tree encroachment, resulting in loss of open patches with herbaceous vegetation. We suggested that this process results in a ground spider community dominated by shade-loving species. At three Mediterranean woodland sites located along a rainfall gradient, we examined the effects on the ground-spider community of experimental removal of the woody vegetation in 1000 m2 plots by cutting and overall plant biomass reduction by grazing and browsing by livestock. Pitfall traps were placed in replicated plots of four treatments (control, cutting, grazing/browsing, and cutting together with grazing/browsing) and in two different habitat patch types (open, woody). ANOVA and multivariate analyses were performed on family abundance by treatment and habitat patch type. Tree-cutting reduced the number of families in plots at two of the three sites. Grazing did not have a significant effect on the number of families or on the ground spider community composition. The spider community of cut-woody patches was more similar to that of open patches than to that of uncut woody patches. Most spider families separated along an axis of open versus woody patches, with woody habitat families predominating at all sites. Families typical of open habitats were positively associated with cut-woody patches as well. The overall effect on ground spider diversity of such manipulations may depend on the scale of habitat changes.

Keywords

• diversity
• family composition
• ordination
• patchiness
• similarity