Rarity patterns and conservation priorities in Cactaceae species from the Southern Central Andes: a case study from the Calchaquíes Valleys, Salta, Argentina

Abstract

In this study, 34 Cactaceae species from the Calchaquíes Valleys, Argentina, were studied to determine 1) species rarity level, 2) proportion of rare species among taxonomic and ecological groups and, 3) whether rareness is consistently distributed throughout the species geographical ranges. We used a model where rarity is defined by the geographic range and the local population size to define species rarity. Rareness was not concentrated in any particular taxonomic or ecological group of Cactaceae; however 28 species were rare at some level. In most species, rarity varied across the geographical range, only five species remained consistently rare in all the surveyed populations. Six species qualified as extremely rare, all from the Cactoideae subfamily, four endemic to the southernmost Central Andes and differing in their growth forms. Only two of the 34 studied species, appeared as both extremely and consistently rare across its distribution. Determining rarity levels is useful for identifying species that may be in danger and/or in need for further studies. Rarity, used as an indicator of species vulnerability, allowed us, to identify Cactaceae species that are more vulnerable to anthropogenic or natural disturbance, compared with common species. Many of the Cactaceae species identified here as rare were mentioned by IUCN at intermediate categories of extinction. Our approach seems then to yield useful results and rareness in the present context appears to be related with vulnerability to extinction within the southernmost Central Andes.