Environmental Harshness Decreases ant β-Diversity Between Salt Marsh and Neighboring Upland Environments

Abstract

Understanding how wetland organisms interact with neighbor habitats along environmental gradients is important to recognize wetland integrity and its connectivity at landscape-level. We evaluated whether assemblage characteristics (e.g. α-diversity) of marsh-ants are associated with geographic changes in environmental conditions, and if these factors are associated with marsh-upland dissimilarity in ant species composition (β-diversity). Ant-samples were collected both in the marsh and in the neighboring upland habitat at 5-sites along the South-west Atlantic (SWA) coastline (36°S to 40°S), encompassing two-distinct biogeographic regions. Generalized Linear Models showed that at the marsh scale, ant occurrence increased with maximum temperature and Spartina densiflora cover, but decreased with total-plant cover. Ant richness increased with salinity, S. densiflora cover and marsh area; and ant α-diversity increased with S. densiflora cover and decreased with total marsh plant cover and plant height. Composition of ant assemblages differed between the marsh and the upland habitat depending on the site, and β-diversity decreased with precipitation, salinity, tidal amplitude and α-diversity of the herbaceous stratum. Then, the abundance and α-diversity of ants varied along SWA marshes in relation to changes in local environmental factors and the regional landscape. Moreover, changes in species characteristics across coastal-landscape seem to interact with environmental gradients, resulting in reduced β-diversity values with increasing environmental harshness. Thus, our results suggest that the link of geographic changes in the physical environment with the changes in species traits drives the variation in marsh-upland dissimilarity across the space.