Nonrandom extinction patterns can modulate pest control service decline.

Changes in biodiversity will mediate the consequences of agricultural intensification and expansion for ecosystem services. Regulating services, like pollination and pest control, generally decline with species loss. In nature, however, relationships between service provision and species richness are not always strong, partially because anthropogenic disturbances purge species from communities in nonrandom orders. The same traits that make for effective service providers may also confer resistance or sensitivity to anthropogenic disturbances, which may either temper or accelerate declines in service provision with species loss. We modeled a community of predators interacting with insect pest prey, and identified the contexts in which pest control provision was most sensitive to species loss. We found pest populations increased rapidly when functionally unique and dietary-generalist predators were lost first, with up to 20% lower pest control provision than random loss. In general, pest abundance increased most in the scenarios that freed more pest species from predation. Species loss also decreased the likelihood that the most effective service providers were present. In communities composed of species with identical traits, predators were equally effective service providers and, when competing predators went extinct, remaining community members assumed their functional roles. In more realistic trait-diverse communities, predators differed in pest control efficacy, and remaining predators could not fully compensate for the loss of their competitors, causing steeper declines in pest control provision with predator species loss. These results highlight diet breadth in particular as a key predictor of service provision, as it affects both the way species respond to and alter their environments. More generally, our model provides testable hypotheses for predicting how nonrandom species loss alters relationships between biodiversity and pest control provision.