Baxter Peter W J, Sabo John L, Wilcox Chris, McCarthy Michael A, Possingham Hugh P
School of Botany, University of Melbourne, Parkville, VIC 3010, Australia.
Conserv Biol. 2008 Feb;22(1):89-98. doi: 10.1111/j.1523-1739.2007.00850.x.
predators can have pronounced effects on naïve prey species; thus, predator control is often essential for conservation of threatened native species. Complete eradication of the predator, although desirable, may be elusive in budget-limited situations, whereas predator suppression is more feasible and may still achieve conservation goals. We used a stochastic predator-prey model based on a Lotka-Volterra system to investigate the cost-effectiveness of predator control to achieve prey conservation. We compared five control strategies: immediate eradication, removal of a constant number of predators (fixed-number control), removal of a constant proportion of predators (fixed-rate control), removal of predators that exceed a predetermined threshold (upper-trigger harvest), and removal of predators whenever their population falls below a lower predetermined threshold (lower-trigger harvest). We looked at the performance of these strategies when managers could always remove the full number of predators targeted by each strategy, subject to budget availability. Under this assumption immediate eradication reduced the threat to the prey population the most. We then examined the effect of reduced management success in meeting removal targets, assuming removal is more difficult at low predator densities. In this case there was a pronounced reduction in performance of the immediate eradication, fixed-number, and lower-trigger strategies. Although immediate eradication still yielded the highest expected minimum prey population size, upper-trigger harvest yielded the lowest probability of prey extinction and the greatest return on investment (as measured by improvement in expected minimum population size per amount spent). Upper-trigger harvest was relatively successful because it operated when predator density was highest, which is when predator removal targets can be more easily met and the effect of predators on the prey is most damaging. This suggests that controlling predators only when they are most abundant is the "best" strategy when financial resources are limited and eradication is unlikely.
捕食者会对未经历过捕食压力的猎物物种产生显著影响；因此，为保护受威胁的本地物种，控制捕食者往往至关重要。彻底根除捕食者虽然理想，但在预算有限的情况下可能难以实现，而抑制捕食者数量则更可行，且仍可能实现保护目标。我们使用基于洛特卡 - 沃尔泰拉系统的随机捕食者 - 猎物模型，来研究捕食者控制实现猎物保护的成本效益。我们比较了五种控制策略：立即根除、移除固定数量的捕食者（固定数量控制）、移除固定比例的捕食者（固定比率控制）、移除超过预定阈值的捕食者（上限触发捕捞）以及每当捕食者数量降至较低预定阈值以下时移除捕食者（下限触发捕捞）。我们考察了在管理人员总能按预算移除每种策略所针对的全部捕食者数量的情况下，这些策略的表现。在此假设下，立即根除对猎物种群的威胁降低最多。然后，我们假设在低捕食者密度下移除捕食者更困难，研究了管理成功率降低对实现移除目标的影响。在这种情况下，立即根除、固定数量和下限触发策略的表现显著下降。尽管立即根除仍产生了最高的预期最小猎物种群规模，但上限触发捕捞产生了最低的猎物灭绝概率和最大的投资回报率（以每花费金额所带来的预期最小种群规模的改善来衡量）。上限触发捕捞相对成功，因为它在捕食者密度最高时起作用，此时更容易实现捕食者移除目标，且捕食者对猎物的影响最为严重。这表明，当财政资源有限且不太可能根除捕食者时，仅在捕食者数量最多时对其进行控制是“最佳”策略。
