Plant functional groups modulate the effects of landscape diversity on natural predators

Abstract

In agricultural landscapes, pests and natural predators are collectively influenced by crop structures, landscape composition, and landscape configuration. While the independent effects of these factors on pests and their natural enemies have been investigated, their interactive effects remain unclear. This study was performed in 15 heterogeneous landscapes centered on mango orchards, with surrounding habitats (forest, rubber, areca, longan, and farmland) sampled to assess their role as sources and habitats for pests and predators. We characterized the landscape composition (habitat cover and landscape diversity) and configuration (patch density). Orchards with and without understory plants were selected using paired designs within each landscape. We measured the abundances of pests (thrips) and predators (lacewings) in the orchards and their surrounding habitats. The independent and interactive effects of landscape composition, configuration, and understory plants on pests and predators were analyzed. Additionally, we explored how the functional groups of understory plants (linear-leaved and nonlinear-leaved) influenced the abundance of pests and predators. Landscape diversity, forest presence, and understory plants showed insignificant effects on thrips but significantly affected lacewing abundance. Specifically, lacewing abundance in orchards was significantly higher in landscapes with forest presence than in those without forest presence. Orchards with understory plants showed significantly higher lacewing abundance than orchards lacking such vegetation. Landscape diversity was negatively correlated with lacewing abundance; however, this effect was only observed in forested landscapes. More importantly, understory plants mitigated the adverse effects in landscapes with forests on lacewing abundance mainly because understory nonlinear-leaved plants, rather than linear-leaved plants, promoted natural predator abundance. This study provides evidence that the effects of landscape diversity are co-dependent on forest presence, plant functional groups, and species identity. We recommend preserving forest in agricultural landscapes and retaining understory nonlinear-leaved plants to collectively address the negative impacts of landscape diversity on natural predators.