Plant-animal interactions in the Caatinga: Overview and perspectives

Abstract

Interactions between plants and animals are extremely diverse and operate as both evolutionary and ecological forces for angiosperms, insects, and many groups of vertebrates. In this chapter we present a brief overview of plant-animal interactions in the Caatinga, describe some interaction responses to human disturbances, and address future scientific agenda. Despite climatic restrictions, plant pollination in Caatinga is very specialized, involving 13 different systems and a high percentage of pollination by vertebrates. Abiotic seed dispersal prevails, but the Caatinga is a global hotspot for myrmecochory, with more than 100 woody species depending on ants for seed dispersal; saurochory is also a distinctive dispersal mode in the Caatinga. Extrafloral nectary-bearing plants also represent a conspicuous feature of the Caatinga flora (15% of woody species and 40% of individuals at the local scale), with protection against herbivores provided by a diverse ant community. Finally, leaf-cutting ants (LCAs) and exotic goats represent the most voracious herbivores (the LCA herbivory rate is 20% of leaves in their foraging areas). It has already been demonstrated that human disturbances can reduce the diversity of pollination systems and high-quality ant dispersal services in the Caatinga. On the other hand, LCA colony density usually increases along roads and other human-disturbed habitats, with increments in the herbivory rate due to the proliferation of palatable plants (e.g., native Euphorbiaceae and weeds). As climate and land use changes proceed, a substantial proportion of the Caatinga plant-animal interactions are likely to be disrupted or even become extinct, with unanticipated impacts on biodiversity persistence and sustainability in this biologically unique region.