Setting thresholds for pest control: how does pest density affect resource viability?

Conservation in New Zealand is largely focused on reducing the impact introduced mammals have on the abundance of indigenous species. Conservation managers have a range of strategies they can employ to control these pests, but the combination that maximises conservation gains depends on the protection 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 control can increase control effectiveness by reducing opportunity costs. However. complex trophic relationships between pests and resources mean that thresholds which minimise the costs of controlling pests without reducing the viability of threatened populations to unacceptable levels will often be difficult to identify. Here we review three general consumer-resource models in the context of pest control. (1) the damage function based on the functional response of pests to resource abundance, (2) density dependent predator-prey models, and (3) interactive models. Damage functions can be used to set threshold pest densities that achieve tactical but not strategic conservation outcomes. Density dependent predator-prey models can be used to set threshold pest densities that have strategic consequences for resource conservation, 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 that are responsive to pest density. resource abundance and prevailing environmental conditions. We advocate this modelling framework as a basis for setting control thresholds for pests in New Zealand. (C) 2001 Elsevier Science Ltd. All rights reserved.