Setting thresholds for pest control: how does pest density affect resourceviability?

Conservation in New Zealand is largely focused on reducing the impact intro duced mammals have on the abundance of indigenous species. Conservation man agers have a range of strategies they can employ to control these pests, bu t the combination that maximises conservation gains depends on the protecti on each strategy affords, and the scale at which it can be applied. Given a limited budget, the use of threshold pest densities to initiate pest contr ol can increase control effectiveness by reducing opportunity costs. Howeve r. complex trophic relationships between pests and resources mean that thre sholds which minimise the costs of controlling pests without reducing the v iability of threatened populations to unacceptable levels will often be dif ficult to identify. Here we review three general consumer-resource models i n the context of pest control. (1) the damage function based on the functio nal response of pests to resource abundance, (2) density dependent predator -prey models, and (3) interactive models. Damage functions can be used to s et threshold pest densities that achieve tactical but not strategic conserv ation outcomes. Density dependent predator-prey models can be used to set t hreshold pest densities that have strategic consequences for resource conse rvation, but are limited in their scope where pest or resource abundance is influenced by density independent environmental perturbation. Interactive models can be used to identify thresholds for imposition of pest control th at are responsive to pest density. resource abundance and prevailing enviro nmental conditions. We advocate this modelling framework as a basis for set ting control thresholds for pests in New Zealand. (C) 2001 Elsevier Science Ltd. All rights reserved.