Metacommunity theory predicts that habitat fragmentation should reduce food chain length and food web complexity. Generalist predators’ diets integrated over time should reflect fragmentation’s changes to food webs. We tested how the trophic niche of a generalist predator, the funnel-web spider Atrax sutherlandi, changed with fragmentation in a large-scale, long-term habitat fragmentation experiment, the Wog Wog Habitat Fragmentation Experiment (Australia). We hypothesized that we would observe reduced trophic positions (estimated by δ15N) and isotopic niche areas (from a δ13C-δ15N biplot) in populations of A. sutherlandi from native eucalypt forest fragments and pine plantation matrix compared to continuous eucalypt forest. We collected A. sutherlandi from pitfall traps at Wog Wog and analyzed individuals for δ13C and δ15N.
Results/Conclusions
We found that fragmentation did not reduce δ15N or isotopic niche area of A. sutherlandi. Individuals in the matrix and fragments were on average 1.6 ‰ and 0.62‰ higher in δ15N, respectively, than individuals in controls. Contrary to expectations, stable isotopic niches were largest in the matrix (2.86 ‰2), followed by fragments (1.60 ‰2), and smallest in the continuous forest (1.25‰2). Thus, contrary to predictions from theory, habitat fragmentation appeared to increase the trophic position and trophic breadth of the generalist predator, A. sutherlandi. We speculate that these changes may instead be driven by variation in leaf litter depth.