Landscape characteristics influence pest control services in macadamia orchards and shape bird and bat assemblages

Abstract

Biological pest control is a vital ecosystem service in agriculture, with birds and bats acting as key natural predators of crop pests. However, their relative contributions and how these vary with landscape characteristics remain unclear. We examined the roles of birds and bats in pest control in intensively managed macadamia orchards in South Africa. Using visual and acoustic monitoring, nut quality assessments, and predator exclusion experiments, we examined their influence on insect damage and the effect of landscape characteristics (i.e., cover of natural habitat, altitude, and orchard edges) on predator diversity, composition, and pest control. Excluding birds and bats increased insect damage to nuts from 6.2% to 10.7% (a 70% relative increase). Bat activity reduced damage, with stronger effects in areas with less cover of natural habitat. In contrast, bird abundance did not affect insect damage. Despite these benefits, predator exclusion did not impact yield. Instead, yield followed a unimodal relationship with cover of natural habitat, peaking at 60% and remaining substantially elevated even in landscapes with higher habitat cover. Bird and bat species richness remained high across orchards. Bird community composition varied between orchard edges and centers: forest species were more common at edges, while open-habitat species dominated centers. Bat diversity increased with natural habitat cover but was unaffected by other landscape characteristics. Our findings underscore the importance of natural habitats for biological pest control in agricultural landscapes. By promoting richness and activity of complementary functional predator groups, natural habitats can improve crop quality by indirectly reducing insect damage and thus contribute considerably to agricultural productivity.