The case for ‘bottom-up’ pest management

The introduction of some animal and plant pest species in New Zealand has facilitated the establishment and success of other introduced pest species. Classic examples include rodents and rabbits, which have provided prey for a number of introduced mammalian predator species. Control of these introduced predators in New Zealand has historically focussed on removing them directly by lethal means. This approach suffers from density-dependent population responses that accelerate population recovery at low population densities. I suggest adopting an ecologically-based approach to pest control that breaks the interactive linkages between invasive mammalian pests at high trophic levels and the other introduced species that they rely on as their primary food resource. Some of these primary food species are, in turn, affected by land management practices and land-use policy. Removing the primary food resource for introduced pests at high trophic levels should, in theory, weaken the density-dependent responses that reduce the impact of lethal control. This ‘bottom-up’ form of pest control has the added advantage of reducing pest impacts at lower trophic levels. A greater emphasis on bottom-up pest management that targets lower trophic levels could greatly enhance current tactical approaches that focus directly on pests at higher trophic levels. Examples of where this approach could assist management of introduced pests in New Zealand and overseas are discussed.