Contribution of common vs. rare species to species diversity patterns in conservation corridors

Abstract

Abstract Understanding how common vs. rare species contribute to species richness patterns, and are differentially affected by landscape features, is essential for effective conservation monitoring and planning. Using common vs. rare dung beetles and ants, we test how species rarity shapes richness patterns across a timber plantation mosaic with remnant natural grassland conservation corridors as a mitigation measure. We then determine how environmental and spatial factors shape assemblage composition of common and rare grassland species, and how matrix-derived species influence these patterns. For each taxon, species were ranked from common-to-rare, and from rare-to-common. This ranking gave sequences of species richness patterns for increasing numbers of species. Along each stage of these two sequences, species richness of the sub-assemblage was correlated with that of the whole assemblage. This was repeated with matrix-derived species excluded. Deconstructing the species response matrices according to species traits, variation in composition of common vs. rare grassland specialists, as well as in matrix-derived species, were related to environmental (natural environmental heterogeneity and habitat quality) and spatial factors. For both taxa, common species reflected overall species richness patterns better than rare species. Matrix-derived species reduced the contribution of rare species to species richness patterns of dung beetles. Environmental variables were relatively more important for rare species than for common species composition, especially rare ants. We found that in a fragmented landscape: 1) common species reflect overall species richness patterns better than rare species, 2) overall species richness patterns do not reflect those of rare species, 3) the relative influence of regional- and local-scale factors are determined by an organism’s scale of life function, 4) rare species are especially affected by habitat quality, 5) knowledge of ecological processes governing communities in landscape mosaics are crucial for conserving grassland species diversity within these corridors.