Abstract

Virtually all animals are predators, prey or both. Today, there is compelling evidence that predation often limits prey populations and increasing interest has been focused on measures for decreasing predation pressures through predator control. This is true both for game management, where the aim is to increase the opportunity for culling game populations, and in conservation, where the aim is increasing the viability of endangered populations.

The scientific literature on predator control was reviewed and 46 experimental studies fit the search criteria. There was a clear significant effect of predator control on prey populations, such that predator control usually led to increasing breeding success and population numbers. This was true both for mammals and birds, unless prey numbers already were so high that competition limited prey populations. The results were in agreement with previous reviews of the literature, mainly dealing with older empirical studies. Overall, there is a convincing body of evidence on the positive effects of predation control on prey populations.

The positive effects were, however, in many cases relatively short-lived, unless predator control remained in place, due to immigration of predators. Furthermore, predation control targeting single species resulted in other predators increasing their predation pressure in several cases, thus preventing positive effects on prey numbers. Control of top predators may even increase predation pressures through so called ‘meso-predator release’, which may occur when top predators also prey on smaller predators. For instance, control programs aimed at reducing red foxes have led to increasing numbers of feral cats and as a consequence increasing predation pressures on small mammals.

Predation pressures may be reduced by removing predators or by reducing predator effectiveness. Changing the habitat in order to provide cover can in many cases be more cost effective than reducing predator numbers, which can be time consuming and requires continuous or repeated efforts in order to be effective. The positive effects of direct predation control, i.e. removing predators, and improving the habitat are, however, in many cases additive. Thus, combining such measures is likely to benefit prey populations more than implementing either form of measure by itself. Successful predator control in many cases requires careful planning, combining measures and controlling a significant part of the predator guild. Predator control should be seen as a flexible measure, where it is necessary to review the effects on predators and prey as one goes along; it may often be necessary to adapt the methods, effort or focus. This is especially true in conservation work, where it may be crucial to achieve the goal quickly in order to prevent extinction of the prey population.

The question of whether predator control should be implemented relies on ethical, rather than biological, considerations. It is, however, necessary to have a biological understanding of the consequences of predator control in order to make the decision. It is important to make a distinction between biological and ethical issues when deciding on appropriate measures. Furthermore, it is important to realise that the ethical considerations may be identical, or similar, for very different measures. Increasing the amount of cover in order to reduce predation pressure, and removing predators by shooting or catching them, ultimately strives to achieve the same goal: benefitting a prey population by reducing the success of a predator. Only the proximate mechanisms for achieving the goal differ. Indirect predation control methods, i.e. reducing the efficiency of the predators, may entail ethical problems of their own, as compared to direct predator control. For instance, predator young may starve when the success rate of the predator decreases.

Predator control provides a powerful measure for benefitting prey populations when used correctly, both in game management and conservation. In order to be effective it should be regarded as a flexible tool best combined with other measures, such as improving the habitat for prey populations.

Keywords

predation; predatorkontroll; viltförvaltning; naturvård; rovdjur

Published in

Viltforum
2008, number: 2008:1
ISBN: 978-91-977510-0-1
Publisher: Svenska jägareförbundet

UKÄ Subject classification

Fish and Wildlife Management


Permanent link to this page (URI)

https://res.slu.se/id/publ/116068