Individual specialization among generalist predators: Testing the assumptions of selective predator removal programs intended to enhance endangered prey populations

Background/Question/Methods

Selective removal of “problem” predators is sometimes proposed as a means to enhance endangered prey populations. Justification for these lethal control programs rests on two key assumptions: 1) only a specialized subset of the predator population is responsible for the conflict, and 2) that the conflict will cease after those individuals are removed. Many of these cases require prompt action and are of great public interest (e.g., Galapagos sharks/Hawaiian monk seals, mountain lions/bighorn sheep, California sea lions/salmon). It is important to evaluate the factors influencing management success in these cases. In particular, to what degree does violating the aforementioned assumptions influence the long-term success of management as it relates to increasing the size of an endangered prey population? A theoretical agent-based model was developed in Netlogo 5.0.2 to test the effectiveness of selective removal programs in scenarios that differ in three key ways: 1) the degree to which individual predators specialize on endangered prey; 2) the mode by which individuals become specialized; and 3) the accuracy of lethal removal efforts.

Results/Conclusions

Preliminary results suggest that the most important factor for management success is the accuracy of removal efforts. When managers accurately identify and remove predators that are repeatedly consuming endangered prey, there is a significant increase in the endangered prey population. In contrast, there are marked declines in the endangered prey population across all scenarios involving imperfect management in which randomly encountered predators are removed without knowing whether they have been consistently consuming endangered prey. The degree to which predators specialize on endangered prey (i.e., their willingness to supplement their diet with alternative prey) is only important in cases when removal is accurate and predators specialize in endangered prey after multiple successful encounters with them. Contrary to expectations, the mode of predator specialization (i.e., whether the predator becomes specialized via genetic inheritance, learning from experience, or random chance) does not significantly influence management success in the context of this analysis. Further model development and analyses are warranted; however, these interim results suggest that the success of selective predator removal programs intended to enhance endangered prey populations is more dependent on accurate identification of problem individuals than the degree and mode of their specialization in endangered prey.