Within-corridor heterogeneity is more important than corridor design for maintaining butterfly functional and taxonomic diversity

Local and landscape features influence the spatial distribution of biodiversity. At the landscape scale, heterogeneity has compositional and configurational components that can be measured at different resolutions of conservation planning. We assess the importance of local and landscape features measured at different planning resolutions for maintaining taxonomic and functional butterfly diversity. In remnant conservation corridors that dissect alien tree plantations, butterflies were sampled along a gradient of successional stages, from open and recently burned grasslands to closed-canopy woody habitats. Changes in local vegetation structure were represented by measures of canopy cover. At the landscape scale, compositional and configurational heterogeneity were measured at two resolutions: a simple binary classification of suitable habitat versus unsuitable transformed habitat, and a classification that accounts for the different successional stages within corridors (i.e. within-corridor heterogeneity). Butterfly assemblages were characterized using taxonomic (Simpson's diversity index) and functional indices (Rao's quadratic entropy). The relationship between environmental filters and species traits was further assessed using multivariate modelling. Taxonomic diversity did not reflect functional diversity, as the latter showed differential trait specific responses to local vegetation structure. For both functional and taxonomic diversity, local and landscape variables representing within-corridor heterogeneity were more important than landscape variables measured at the coarser planning resolution. Butterfly diversity showed a negative relationship with increasing edge density between grassy and woody habitats. Synthesis and applications. To promote the taxonomic and functional dimensions of biodiversity, management should aim to maintain both open- and closed-canopy habitats within corridors. These habitats should be contiguous, and corridors as wide as possible, to increase the patch size of contiguous habitat while reducing the proportion of edge.