Patch-scale edge effects do not indicate landscape-scale fragmentation effects

Abstract

Negative landscape-scale fragmentation effects are often inferred from negative patch-scale edge effects. I tested this cross-scale extrapolation using two evaluations. First, I searched for studies that estimated the direction of both a patch-scale edge effect and a landscape-scale fragmentation effect. The directions were concordant and discordant in 55% and 45% of cases, respectively. Second, I extracted from the literature a sample of landscape-scale fragmentation effects on individual species. Then, for each species I searched for studies from which I could calculate the slope of its patch-scale edge effect. Species showing negative patch-scale edge effects were nearly equally likely to show negative or positive landscape-scale fragmentation effects, and likewise for species showing positive patch-scale edge effects. The results mean that the efficacy of policies related to habitat fragmentation cannot be inferred from observed patch-scale edge effects. Such policies require landscape-scale evidence, comparing species' responses in landscapes with different levels of fragmentation.