Corridors are envisioned to benefit biodiversity — re-connecting landscapes that have become fragmented, and providing safe passage for plants and animals across landscapes that are increasingly dominated by humans. Yet, corridors could cause harm to biodiversity, if as Simberloff and colleagues cautioned, corridors move harmful species (think invasives, or predators of species we are trying to conserve) or spread disturbances. On balance, research on corridors supports their beneficial effects. Yet, the one way that research has shown corridors, especially narrow corridors, can be harmful is by creating negative edge effects. A new study appearing in Ecology by Åström and Pärt show new ways that narrow corridors create negative edge effects.
In the study, a microcosm experiment of microarthopods inhabiting mosses, the authors manipulated the presence of corridors, along with the degree of disturbance and the severity of matrix habitat. They found corridors to have negative effects on one group of mites, likely because narrow corridors permitted greater influence of harsh matrix conditions within patches, or because they provided more places for mites to leave moss habitats and enter the matrix. Wider corridors would have alleviated both of these issues.
Microcosm studies like this one, when viewed across a larger group that has been conducted on systems of microarthropods or protists, have made two more general contributions to understanding the role of corridors. First, perhaps because they are more controlled and thus able to understand more complex interactions between species, microcosm experiments have shown more varied responses in their assessment of corridors than studies in larger ecosystems (Gilbert-Norton, et al. 2010). In this study, predatory species responded differently from other mites and benefited from corridors, confirming predictions that predators may be more severely affected by predators. Second, this study and other studies of microcosms have been among the few that have been able to test the effects of corridors on populations. This is ironic, as corridors are typically created in conservation to increase population persistence. In general, more studies are needed that address the population consequences of corridors.
Åström, J., and T. Pärt. 2013. Negative and matrix-dependent effects of dispersal corridors in an experimental metacommunity. Ecology 94:72-82.
Gilbert-Norton, L., R. Wilson, J. R. Stevens, K. H. Beard. 2010. A meta-analytic review of corridor effectiveness. Conservation Biology 24(3): 660-668.