Habitat conversion, extinction thresholds, and pollinator services in agroecosystems

A considerable portion of our global food supply depends critically on the coevolved relationship between flowering plant and insect pollinators. Fruiting of many agriculturally important plant species depends fully or partially on insect pollinators. Native pollinators are an important source of pollination services to many crops. Landscape conversion to agricultural use threatens many pollinator species risking loss of pollinator services and has raised concern over widespread pollination limitation in agroecosystems. Loss of native pollinators may be offset through husbandry of domesticated pollinators, but at the risk of dependence on a pollinator monoculture susceptible to disease or environment change. Understanding the effects of agricultural habitat conversion on the key link between native pollinators and crop production is an important challenge for ecology. Currently, no theory offers an examination of the specific impacts of amount and pattern of habitat conversion on pollinator species in agroecosystems. This paper studies the problem of pollinator limitation in fragmented agricultural landscapes. A pair of models is presented -- one an individual-based simulation and another composed of difference equations that mimic the behavior of the simulation model in the mean-field limit. Bifurcation analysis of the models indicates a cusp at a threshold amount of habitat loss. When pollinators are subsidized by crops, the dynamics are more complex with state-dependent rules for colonization. Some guidelines are developed for managing pollinators in agricultural landscapes.