Montana Cooperative Wildlife Research Unit, University of Montana, Missoula, Montana, 59812, USA.
U.S. Geological Survey, Montana Cooperative Wildlife Research Unit, University of Montana, Missoula, Montana, 59812, USA.
Ecology. 2017 Jul;98(7):1829-1838. doi: 10.1002/ecy.1860. Epub 2017 Jun 8.
Increased perceived predation risk can cause behavioral and physiological responses to reduce direct predation mortality, but these responses can also cause demographic costs through reduced reproductive output. Such indirect costs of predation risk have received increased attention in recent years, but the relative importance of direct vs. indirect predation costs to population growth (λ) across species remains unclear. We measured direct nest predation rates as well as indirect benefits (i.e., reduced predation rates) and costs (i.e., decreased reproductive output) arising from parental responses to perceived offspring predation risk for 10 songbird species breeding along natural gradients in nest predation risk. We show that reductions in seasonal fecundity from behavioral responses to perceived predation risk represent significant demographic costs for six of the 10 species. However, demographic costs from these indirect predation effects on seasonal fecundity comprised only 12% of cumulative predation costs averaged across species. In contrast, costs from direct predation mortality comprised 88% of cumulative predation costs averaged across species. Demographic costs from direct offspring predation were relatively more important for species with higher within-season residual-reproductive value (i.e., multiple-brooded species) than for species with lower residual-reproductive value (i.e., single-brooded species). Costs from indirect predation effects were significant across single- but not multiple-brooded species. Ultimately, demographic costs from behavioral responses to offspring predation risk differed among species as a function of their life-history strategies. Yet direct predation mortality generally wielded a stronger influence than indirect effects on seasonal fecundity and projected λ across species.
感知到的捕食风险增加会导致行为和生理反应，以降低直接捕食死亡率，但这些反应也会通过降低繁殖量而导致种群数量减少。近年来，捕食风险的这种间接成本受到了越来越多的关注，但直接与间接捕食成本对物种种群增长（λ）的相对重要性仍不清楚。我们测量了 10 种沿巢捕食风险自然梯度繁殖的鸣禽的直接巢捕食率，以及由于亲鸟对感知到的后代捕食风险的反应而产生的间接利益（即降低的捕食率）和成本（即繁殖量减少）。我们表明，六种物种中的六种由于对感知到的捕食风险的行为反应而导致季节性繁殖力下降，这代表了重大的种群数量减少成本。然而，这些间接捕食效应对季节性繁殖力的影响造成的种群数量减少成本仅占跨物种平均累积捕食成本的 12%。相比之下，来自直接捕食死亡率的成本占跨物种平均累积捕食成本的 88%。来自直接后代捕食的种群数量减少成本对于具有较高季节性剩余繁殖价值的物种（即多次繁殖物种）相对更为重要，而对于具有较低剩余繁殖价值的物种（即单次繁殖物种）则相对不重要。间接捕食效应的成本在单次繁殖物种中是显著的，但在多次繁殖物种中则不显著。最终，由于其生活史策略的不同，对后代捕食风险的行为反应造成的种群数量减少成本在物种之间存在差异。然而，直接捕食死亡率通常比间接影响对跨物种的季节性繁殖力和预测的λ具有更强的影响。
