Bat and bird exclusion but not shade cover influence arthropod abundance and cocoa leaf consumption in agroforestry landscape in northeast Brazil

Abstract

Bats and birds play important roles as arthropod predators in top-down control. Both groups are represented by a large number of species in agroforests, but are likely to respond negatively to management intensification. This study investigates the potential role of bats and birds on arthropod pest control in shaded cacao plantations through a field experiment. We tested if bat and/or bird exclusion from cacao trees leads to higher arthropod abundance and leaf damage, and conducted the experiment in high and low shade plantations. Our results suggest a complex food web, with at least four trophic levels, connecting top predators to primary producers in cacao agroforests. Bird exclusion increased leaf damage while bat exclusion increased total arthropod and plant-sucking insect relative abundance. Simultaneous bird and bat exclusion increased spider relative abundance, triggering a mesopredator release, which negatively affected herbivore activity and reduced leaf damage. Shade level did not significantly influence observed top-down effects. This finding, coupled with previous knowledge on bat and bird diversity in agroforestry landscapes in southern Bahia, suggests that landscape-scale effects may be more relevant than local shade management for maintaining diverse bird and bat assemblages. Agroforestry systems harbour natural biological control functions played by bats and birds. Because these are highly mobile organisms, large-scale implementation of wildlife-friendly landscapes is likely to be more important for this than local shade management within agroforests.