Spillover of terrestrial arthropod species and beta diversity in perennial crops relative to spatial scale of land-use intensity.
Abstract
Arthropod diversity in agricultural areas is influenced by land-use intensity (LUI) at both local and landscape scales. In agricultural systems, non-crop habitats are important for promoting in-field arthropod diversity, although in perennial orchard systems, boundary contrast (i.e. structural differences between crop and non-crop habitats) may impede spillover of arthropods from non-crop areas. We focus on ground-dwelling arthropods sampled within orchards in the Kogelberg Biosphere Reserve, South Africa, that do not show a strong association with this habitat type (i.e. 'non-cultural' species), and assess the influence of local (in-field scale; FLUI) and landscape scale LUI (LLUI), boundary contrast, cover-crop management, and population effects on species richness, assemblage variation within orchards, and the dissimilarity between assemblages in crop and non-crop habitats (i.e. 'cross-edge dissimilarity'). Higher LLUI (lower amounts of non-crop habitat) was associated with higher in-field species richness but also higher cross-edge dissimilarity (i.e. these habitats were more distinct in certain landscapes). FLUI was important for non-cultural species, especially non-cultural predators and detritivores, for which higher levels of fertilization reduced in-field species richness. Reduced contrast enhanced in-field species richness, but there was limited evidence that this enhanced spillover from non-crop habitats. Synthesis and applications. In production systems with high border contrast and highly productive crop habitats, higher landscape scale land-use intensity can enhance in-field diversity. By supporting a subset of the assemblage able to thrive in both crop and non-crop habitats, this is contributing to community divergence. To promote farmland diversity, we advocate the reduction of agrochemical inputs, production diversification at the landscapes scale, and the incorporation of a network of non-crop corridors and stepping-stone habitats to maintain connectivity and resilience across the landscape.