Behavioral trade-offs and multitasking by elk in relation to predation risk from Mexican gray wolves

Non-consumptive effects of predation can alter foraging time, stress levels, and habitat use by prey, potentially resulting in reduced fitness. However, prey can mitigate the non-consumptive effects of predation by increasing vigilance, chewing and vigilance synchronization (i.e., multitasking), and spatiotemporal avoidance of predators. We quantified the effects of the Mexican wolf (Canis lupus baileyi) predation risk on elk (Cervus canadensis) behavior in the southwestern United States. We conducted behavioral observations on adult female elk and developed predation risk indices using Mexican wolf GPS collar data, locations of elk killed by Mexican wolves, and landscape covariates. We compared a priori models to determine the best predictors of adult female behavior and multitasking, separately. Metrics that quantified both spatial and temporal predation risk were top predictors in both datasets. Adult female vigilance was positively associated with increased predation risk. Increased predation risk had little effect on the probability of foraging, but resulted in decreased time spent resting. In a post hoc analysis, the effect of predation risk on foraging and resting differed across diurnal periods. During midday when wolf activity was relatively low, the probability of foraging increased while resting decreased, in areas with high spatial predation risk. During crepuscular periods when elk and wolves were most active, increased predation risk was associated with increased vigilance and slight decreases in foraging. Our results suggest elk are temporally avoiding predation risk from Mexican wolves by trading resting for foraging, a trade-off often not evaluated in behavioral studies. The probability of multitasking increased with predation risk, suggesting that adult female elk may be offsetting the non-consumptive effects of risk on feeding time. These results highlight potentially important but often excluded behaviors and trade-offs prey species may use to reduce the indirect effects of predation and contribute additional context to our understanding of predator-prey dynamics.

Methods
See methods section in manuscript and supplementary material file for details.

捕食非消耗效应（non-consumptive effects of predation）可改变猎物的取食时长、应激水平与栖息地利用方式，进而可能降低其适合度。不过，猎物可通过提升警戒行为、同步咀嚼与警戒（即多重任务处理）以及时空上规避捕食者，来缓解捕食非消耗效应的影响。本研究针对美国西南部区域内墨西哥狼（Canis lupus baileyi）的捕食风险对加拿大马鹿（Cervus canadensis）行为的影响展开量化分析。研究人员对成年雌性加拿大马鹿进行行为观察，并基于墨西哥狼GPS项圈（GPS collar）数据、被墨西哥狼捕食的马鹿位置数据以及景观协变量，构建了捕食风险指数。随后分别对比先验模型（a priori models），以确定成年雌性马鹿行为与多重任务处理的最优预测因子。同时量化时空捕食风险的指标在两类数据集的分析中均为最优预测因子。成年雌性马鹿的警戒行为与捕食风险升高呈显著正相关。捕食风险升高对取食概率的影响较弱，但会导致马鹿的休息时长减少。事后分析（post hoc analysis）显示，捕食风险对取食与休息行为的影响随昼夜时段存在显著差异：在狼活动相对较低的正午时段，空间捕食风险较高的区域内，马鹿的取食概率上升而休息时长下降；在马鹿与狼活动最为频繁的晨昏（crepuscular）时段，捕食风险升高与警戒行为增强、取食行为小幅减少相关。研究结果表明，加拿大马鹿通过以休息换取食的策略，在时间维度上规避墨西哥狼的捕食风险——这类行为权衡在现有行为学研究中常被忽视。多重任务处理的发生概率随捕食风险升高而上升，提示成年雌性加拿大马鹿或可通过该策略抵消捕食风险对取食时长带来的非消耗效应。本研究结果凸显了猎物物种用以降低捕食间接影响的一类潜在关键却常被忽略的行为与权衡策略，为我们深入理解捕食者-猎物动态（predator-prey dynamics）关系提供了额外的研究视角。

方法
详见论文正文方法部分及补充材料文件。