Vertical stratification of seed-dispersing vertebrate communities and their interactions with plants in tropical forests.

Abstract

Vertical stratification (VS) is a widespread phenomenon in plant and animal communities in forests and a key factor for structuring their species richness and biodiversity, particularly in tropical forests. The organisms composing forest communities adjust and shape the complex three-dimensional structure of their environment and inhabit a large variety of niches along the vertical gradient of the forest. Even though the degree of VS varies among different vertebrate groups, patterns of compositional stratification can be observed across taxa. Communities of birds, bats, primates, and non-flying small mammals are vertically stratified in terms of abundance, species richness, diversity, and community composition. Frugivorous members of these taxa play important roles as seed dispersers and forage on fruit resources that, in turn, vary in quantity and nutritional value along the vertical gradient. As a consequence, plant-seed disperser interaction networks differ among strata, which is manifested in differences in interaction frequencies and the degree of mutual specialization. In general, the canopy stratum is composed of strong links and generalized associations, while the lower strata comprise weaker links and more specialized interactions. Investigating the VS of communities can provide us with a better understanding of species habitat restrictions, resource use, spatial movement, and species interactions. Especially in the face of global change, this knowledge will be important as these characteristics can imply different responses of species and taxa at a fine spatial scale.