Split distance: a key landscape metric shaping amphibian populations and communities in forest fragments. Issue 11 (11th June 2014) - Lion, Marília Bruzzi
Abstract Aim Habitat split isolates forest fragments where terrestrial adults of many amphibian species live from aquatic‐breeding sites where their larvae develop, causing population declines and shifts in community structure. In contrast to most fragmentation theoretical frameworks which point to the relevance of fragment area and isolation, a recent theoretical model predicts that split distance, defined as the shortest distance between a forest fragment edge and the nearby stream, should affect negatively the abundance and occurrence probability of populations in forest fragments and, consequently, their total abundance and species richness. The model further predicts that the quality of the matrix between the two habitats, called split matrix, will modulate such responses. Here, we provide the first test of these theoretical predictions. Location Atlantic Forest, Brazil. Methods Split distance was estimated for all fragments of the Brazilian Atlantic Forest, a highly disturbed biodiversity hotspot. Then, we selected 23 forest fragments, within a 1166‐km2 landscape, in a design that insured orthogonality between split distance (0–2000 m) and fragment size (1.7–30 ha). Split matrix quality (SMQ) and proximity, a measure of the availability of forest around the focal fragment, were estimated and controlled for in the analyses. Using multiple regression analyses with control for spatial autocorrelation, and AIC multimodel inference, we evaluated the relative importance of split distance, SMQ, fragment size and proximity to determine amphibian community and population attributes. Results Most Atlantic Forest fragments were affected by habitat split. Consistent with the theoretical predictions, species richness, abundance and the occurrence probability of many species declined with split distance and increased with SMQ, even when controlling for fragment size and isolation. Main conclusions Split distance can be used as a surrogate for conservation value of forest fragments for aquatic‐breeding amphibians in landscape planning and restoration enterprises.