Fragment Edges Benefit a Common Predator of Pollinators via Bottom-Up Effects

Defaunation following habitat fragmentation typically threatens predators at higher trophic levels, which further alter prey and plants via top-down effects. However, few studies test if fragmented habitats (e.g., forest edges) support predators through bottom-up effects. Here, we tested the effects of habitat fragmentation on multi-trophic interactions involving flowering plants, pollinators, and a common predatory spider (Atypus heterothecus). We found that spider biomass was higher at the edges of large islands than in their interiors, with no significant effect of island area or isolation. Diet analysis revealed that pollinators accounted for 70% of the spider's prey. Furthermore, prey composition differed significantly between edges and interiors, with edge habitats supporting higher prey richness, as well as greater richness and abundance of flowering plants and pollinators. The higher spider biomass was primarily driven by bottom-up effects, while top-down effects were also present but not strong enough to suppress prey biomass. Our findings suggest that conservation strategies in fragmented landscapes could improve the ecological quality of existing edge habitats, while this should be balanced against the need to protect intact interior habitats for sensitive species. By emphasizing resource-mediated trophic interactions, this study provides new insights into how ecological functions may be maintained in fragmented landscapes.