Grassland in South Africa. Credit: WWF.
Edges occur where two habitat types meet, such as a conservation corridor and the lands that surround them. At this interface, biotic and abiotic processes differ from those habitats on either side. These effects spill out away from the edge, moving towards the interior. Species that are sensitive to edges and rely on the interior do best the further you move away from an edge, while other species are edge specialists and rely on edges for habitat.
Because of their irregular shapes and linear nature, conservation corridors make it so multiple edges often come in close proximity to one another. Scaling up from a single corridor, the effects of multiple edges can be explored at a landscape scale. When edges are close to one another, such as when there are several narrow corridors in a landscape, there may not be sufficient habitat for interior species. The effects of these edges may interact as well, and have greater influences on species than a single edge.
To test whether the effect of edges is heightened when multiple edges are close to one another, a new study sampled arthropods in a series of grassland corridors and protected lands in South Africa. A total of 19 corridors, ranging from 135 to 735 meters wide, were sampled using transects.
The Crimson Tip (Colotis danae) is a small butterfly found in South Africa. Credit: Bernard DuPont
Wider corridors resulted in increased species richness, though this pattern did not hold for all species. Within a single corridor, the pattern was driven by species that prefer interior habitats; wider corridors have more interior habitat available, and species that rely on the interior of corridors were those affected by corridor width. At the landscape scale, distance to the nearest edge was more important than the width of the corridor, and this pattern was driven by edge specialist species that live in these transitional habitats.
The authors argue that conservation efforts should focus on preservation of wider corridors, except when a narrow corridor is necessary to connect two high-value habitats to one another. These findings have implications for how we design corridors for smaller species like arthropods, especially those that might have to complete several life cycles to make their way through a single corridor.
Resources:
van Schalkwyk, J., Pryke, J.S., Samways, M.J., and Gaigher, R. 2020. Corridor width determines strength of edge influence on arthropods in conservation corridors. Landscape Ecology 35: 1175–1185.
How do you build a corridor for invertebrates? (February 2020)
