Over-representation of rare species at high diversity sites: insight from the seven forms of rarity on species richness patterns
Journal Article
Overview
abstract
Abstract; Biodiversity is closely linked to rarity. The seven forms of rarity (the interaction of range size, local abundance, and habitat specialization) have informed much work on rarity, and each component is integral to a hypothesized mechanism maintaining or generating diversity. Besides studies of individual components, the seven forms of rarity have typically been considered at large scales, but these forms could also have important implications for differing species richness at local scales. Here, we examined the compositions of the seven forms of rarity across sites in two mountain ranges in Colorado and three taxonomic groups: ants, carrion beetles, and small mammals. We classified species into the seven forms of rarity by mountain range. Then we explored patterns of species counts in each form across sites by species richness, using null models and simulations for comparison. In both mountain ranges, ant species rare or common in all three components were significantly overrepresented, but carrion beetles and small mammals did not differ from expectation. When compared with the mountain range scale, most sites showed significant overrepresentation of common species, and none showed significant overrepresentation of rare species. However, rare species accumulated faster than common species with increasing species richness. Thus, consistently across all three taxa and both mountain ranges, we detected a disproportionate representation of rare species at sites with high richness. This pattern indicates accumulating multi-form rarity as a potential biodiversity mechanism. Whatever the specific role, rarity in multiple forms deserves deeper consideration for conservation prioritization as a potential biodiversity mechanism.
