The relevance of ecoregions and mountainous environments in the diversity and endemism of land gastropods

Abstract

Twenty-five sub-ecoregions make Argentina from southern South America a favored area to study the mutual correspondence between environments and biodiversity. Unfortunately, efforts devoted to study these environments are unbalanced, with the subtropical dry forests less studied than the tropical and subtropical humid ones. Since the limits of ecoregions are based on vegetation criteria, land gastropods represent an independent source of information to test the relevance of sub-ecoregions in different aspects of biodiversity. We ask if land gastropods mirror these traditional diversity patterns when their distributions are framed in the context of sub-ecoregions. Additionally, we want to test if short-range endemic species (SRE) are randomly scattered across the sub-ecoregions. We first built an updated taxonomic checklist and mapped all the valid records compiled to date. Taxonomic richness, taxonomic diversity, and beta-diversity between sub-ecoregions were calculated. We obtained a hierarchical grouping of sub-ecoregions and the respective list of species that significantly support each cluster. We also developed two new analytical resources: a radial plot for showing the species composition of clusters resolved at three taxonomic levels, and a mixed coefficient of distributional size useful to identify SRE from sparse point records. This dimensionless measure of spatial range combines information of both the convex hull area and the length of the minimum spanning tree connecting point localities of presence. The Southern Andean Yungas and Dry Chaco are the species-level richest ecoregions. Although the Paranaense Forest harbors half of the number of species found in the Chaco Serrano, it reaches the highest score of taxonomic diversity because of the eclectic nature of their genera. SRE species are not randomly distributed across the sub-ecoregions, but they broadly overlap with the orographic Peripampasic arc extended over Chaco Serrano and Yungas Forests. SREs are highly dependent on the physical nature of the landscape.