Sites and species contribution to the β-diversity of Odonata assemblages in Haiti: Implications for conservation

Abstract

Understanding the ecological determinants of assemblage diversity in freshwater insects is of crucial importance for conservation biology and environmental management. This is particularly true in Haiti, where severe and ongoing environmental degradation of aquatic ecosystems is a major threat to the local invertebrate fauna. Here, using Odonates assemblages sampled from 67 waterbodies belonging to 14 different Haitian watersheds, we assessed species uniqueness (U) from both rarity based on spatial occupancy and taxonomic species distinctness (TSD), and species contribution to total β diversity (SCBD). We assessed between-site variation in species richness (SR), relative taxonomic distinctness (RTD), mean species uniqueness per site (Mean U), and the contribution of individual sites to total β diversity (LCBD), based on presence-absence data. We then examined the relationships between these variables and the physico-chemical characteristics of the sites. In total, we recorded 49 different odonate species (including two endemic species of conservation interest), belonging to 40 genera and 7 families, with a relatively high percentage (69.4%) of rare species (i.e. occurring in 10% or less of sampled water bodies). TSD was negatively correlated with spatial occupancy, while U was significantly higher in Zygopeteran species compared to Anisopteran species. SR varied among the 67 sites, ranging from 2 to 17 species, while SCBD was positively correlated with site occupancy. Differences in assemblage composition between sites were mainly due to species replacement, while only a few sites had assemblages consisting of a subset of larger assemblages found at other sites. The observed positive correlation between dissimilarity and geographic distance between sites further suggests that the turnover of species may take place over some ecological gradient and/or might be explained by species ecological requirements and limited ability to disperse. LCBD and Mean U increased with increasing altitude and decreasing temperature and conductivity, whereas SR and RTD did not. All variables were independent of pH. Overall, SR and RTD were higher in lotic than in lentic sites, and in sites with natural riparian vegetation compared to sites with anthropogenic or mixed riparian vegetation. Mean U provided a relevant index for site selection for odonates conservation in Haiti, whereas β diversity appeared to be of limited interest for this purpose. Globally, our results advocate the importance of conserving a wide diversity of waterbodies to protect Odonate diversity in Haïti, and particularly in forested areas at > 1000 m altitude.