Environmental filtering both indirectly and directly drives the Dry Tropical Forest species composition and functional composition

Abstract

Soil is a relevant driver of taxonomic, functional and phylogenetic composition at local scales. However, the mechanisms by which the soil act in these components or how these components interact with each other are not elucidated. Herein, we propose to understand the role of soil (environmental filtering) on the turnover of taxonomic and phylogenetic components and their role in determining the functional composition of Seasonally Dry Tropical Forest (SDTF) communities. We sampled all the arboreal individuals with Diameter at Breast Height equal to or higher than 3 cm and collected soil variables of 25 units from five SDTF fragments located in the Brazilian Caatinga Domain. These data enabled us to obtain the taxonomic, functional and phylogenetic composition of each plot, which were then analyzed by Structural Equation Models jointly with the soil variables. Our results suggest that the soil conditions select specific phylogenetic lineages from a regional species pool according to the adaptive potential, which affects the distribution and abundance of species (taxonomic composition). However, it was not possible to establish a direct relationship between the phylogenetic composition and the taxonomic composition, possibly due to the use of labile functional traits in the analysis. We also found that soil acts directly on the functional composition, leading to a differential success of individuals which would represent a direct and indirect effect of taxonomic composition on the functional composition. Thus, we found community aspects result from different ecological mechanisms which act in a continuous and progressive way between functional, phylogenetic and taxonomic composition.