Birds and bats enhance yields in Afrotropical cacao agroforests only under high shade

Abstract

Sub-Saharan Africa produces most of the Earth’s cacao. Although pests cause losses of hundreds of millions annually, the role of cacao pest suppressors remains unknown. We used an exclusion experiment to prevent access of bats and birds to cacao trees and quantified how their absence affected arthropod communities, herbivory, and crop yield. Overall, Mealybugs and other hemipteran pests were more abundant in exclosures. Under heavy shade (90%), cacao trees with vertebrate exclosures had 3.9 times fewer flowers and 3.2 times fewer large pods than control trees, corresponding to losses on average of $478 ha-1y-1. Under low shade cover (10%) however, the opposite pattern was evident: exclosures trees had 5.2 times more flowers and 3.7 times more large pods than control trees, corresponding to savings on average of $796 ha-1y-1. Our study demonstrates that the enormous potential of African bats and birds as pest suppressors is dependent on shade tree management.