SYMP 19-4
The ghost of Gause: Most habitat fragmentation effects are positive
Research dating back to the mid-1900’s suggested positive effects of habitat 'subdivision' on persistence of species and communities. But this work was subsequently eclipsed by four decades of patch-scale research, emanating from the island biogeography paradigm. Extrapolation of patch-scale results to infer landscape-scale effects led to the nearly universal assumption, counter to the earlier work, that habitat fragmentation (independent of habitat loss) reduces biodiversity. This extrapolation produced decades of dubious conservation policy. Empirical work in landscape ecology avoids the patch-to-landscape extrapolation; the landscape, not the patch, is the unit of replication, so the scale of study is matched to the scale of inference. Here, I review landscape-scale studies of effects of habitat fragmentation per se, i.e. effects of habitat subdivision while controlling for effects of habitat amount.
Results/Conclusions
The majority of documented fragmentation effects are positive, suggesting that earlier work was on the right track. Explanations for positive fragmentation effects are myriad, including reduced intra- and inter-species competition, stabilization of predator-prey and host-parasite interactions, spreading of risk, increased landscape complementation, positive edge effects, higher habitat diversity, and higher landscape connectivity. The results of my review imply that conservation policies should aim to maximize the habitat area conserved but, for a given area conserved, priority should not be placed on habitat contiguity.