Tree-Cover Gradients Modulate the Taxonomic and Functional Diversity of Birds in Amazonian Cattle-Ranching Landscapes

Abstract

Cattle-ranching expansion is the major anthropogenic driver transforming forests in the Colombian Amazon. Landscapes typified by low ecological connectivity and simplified arboreal structure limit resource availability and alter avian species composition and functional-trait distributions. This study analyzed the relationship between the taxonomic and functional diversity of bird assemblages across four tree-cover categories (open (OP), semi-open (SO), semi-closed (SC), and closed (CL)) using 491 point counts from 104 cattle-ranching landscape mosaics in the northwestern Colombian Amazon. A trait matrix was compiled for 342 recorded species distributed among four trophic guilds. Margalef, Shannon, and Simpson indices, together with five functional diversity indices, were calculated, and correlation coefficients between indices were estimated by guild and cover type. The tree-cover gradient differentially influenced guild-level richness, evenness, and functionality. In open and semi-closed covers, insectivores showed greater functional richness, with traits adapted to foraging in open habitats, whereas intermediate vegetation supported higher evenness and functional complementarity in frugivores and granivores. Closed covers imposed stronger filtering on trait diversity. The results are consistent with metacommunity dynamics in which local assemblages and functional spillover sustain ecological processes at the mosaic scale. For cattle-ranching landscape management, reducing habitat contrast within the productive matrix and strengthening forest connectivity are recommended to conserve species richness and ecosystem functions.