Environmental and Life Sciences, Trent University, Peterborough, Ontario, Canada.
PLoS One. 2013 Dec 9;8(12):e82344. doi: 10.1371/journal.pone.0082344. eCollection 2013.
Prey can invest in a variety of defensive traits when balancing risk of predation against that of starvation. What remains unknown is the relative costs of different defensive traits and how prey reconcile investment into these traits when energetically limited. We tested the simple allocation model of prey defense, which predicts an additive effect of increasing predation risk and resource availability, resulting in the full deployment of defensive traits under conditions of high risk and resource saturation. We collected morphometric, developmental, and behavioural data in an experiment using dragonfly larvae (predator) and Northern leopard frog tadpoles (prey) subject to variable levels of food availability and predation risk. Larvae exposed to food restriction showed limited response to predation risk; larvae at food saturation altered behaviour, development, and growth in response to predation risk. Responses to risk varied through time, suggesting ontogeny may affect the deployment of particular defensive traits. The observed negative correlation between body size and activity level for food-restricted prey--and the absence of a similar response among adequately-fed prey--suggests that a trade-off exists between behavioural and growth responses when energy budgets are limited. Our research is the first to demonstrate how investment into these defensive traits is mediated along gradients of both predation risk and resource availability over time. The interactions we demonstrate between resource availability and risk level on deployment of inducible defenses provide evidence that both internal condition and extrinsic risk factors play a critical role in the production of inducible defenses over time.
当权衡捕食风险与饥饿风险时，猎物可以投资于各种防御特征。目前尚不清楚的是，不同防御特征的相对成本是多少，以及当能量有限时，猎物如何协调对这些特征的投资。我们测试了猎物防御的简单分配模型，该模型预测捕食风险和资源可用性的增加会产生累加效应，从而在高风险和资源饱和的条件下充分部署防御特征。我们在使用蜻蜓幼虫（捕食者）和北方豹蛙蝌蚪（猎物）的实验中收集了形态、发育和行为数据，这些实验受到食物供应和捕食风险的不同水平的影响。暴露于食物限制的幼虫对捕食风险的反应有限；在食物饱和的幼虫中，行为、发育和生长会根据捕食风险做出改变。风险的反应随时间而变化，这表明个体发育可能会影响特定防御特征的部署。对于食物受限的猎物，我们观察到身体大小和活动水平之间的负相关关系——而在食物充足的猎物中则没有类似的反应——这表明在能量预算有限的情况下，行为和生长反应之间存在权衡。我们的研究首次表明，随着时间的推移，这些防御特征是如何沿着捕食风险和资源可用性的梯度进行投资的。我们在资源可用性和风险水平之间的相互作用，对可诱导防御的部署提供了证据，即内部条件和外在风险因素在可诱导防御的产生中都起着关键作用。
