Taxon-dependent diversity response along a temperate elevation gradient covered by grassland

Abstract

Elevational gradients constitute excellent systems for understanding the mechanisms that generate and maintain global biodiversity patterns. Climatic gradients associated with elevation show strong influence on species distribution in mountains. The study of mountains covered by the same habitat type is an ideal scenario to compare alternatives to the energy hypotheses. Our aim was to investigate how changes in climatic conditions along the elevational gradient drive α- and β-diversity of four taxa in a mountain system located within a grassland biome. We sampled ants, spiders, birds and plants, and measured climatic variables at six elevational bands (with 10 sampling sites each) established between 470 and 1,000 masl on a mountain from the Ventania Mountain System, Argentina. Species richness per site and β-diversity (turnover and nestedness) between the lowest band and upper sites were estimated. For most taxa, species richness declined at high elevations and energy, through temperature, was the major driver of species richness for ants, plants and birds, prevailing over productivity and water availability. The major β-diversity component was turnover for plants, spiders and birds, and nestedness for ants. The unique environmental conditions of the upper bands could favour the occurrence of specialist and endemic species.

Keywords: Ants; Birds; Climatic driver; Energy hypothesis; Mountain; Multi-taxa; Nestedness; Plants; Spiders; Turnover.

Figure 1. Environmental variables along the elevational gradient of Ventana Mountain.

Lines indicate the general linear model (GLM), with a 95% confidence interval. Dots indicate the average values for each elevation band. Temperature = average temperature, main water in soil, SAVI = average SAVI index, mean annual temperature and annual precipitation.

Figure 2. Species richness of the studied taxa (i.e. ants, spiders, birds and plants) along the elevational gradient of Ventana Mountain.

Lines indicate the generalized linear model (GLM) for each taxon, with a 95% confidence interval. Dots indicate the species richness at each sampling site. Points were jittered to avoid overlap.

Figure 3. Taxonomic dissimilarity and its components between the lowest altitudinal band and each sampling site of the upper bands.

Lines indicate the generalized linear model (GLM) for each taxon, using beta distribution with a 95% confidence interval. The x-axis indicates the elevation (masl) of each upper band.