Environmental & Life Sciences Graduate Program and Department of Biology, Trent University, 1600 West Bank Dr., Peterborough, ON, K9J 7B8, Canada.
Oecologia. 2010 Jun;163(2):395-404. doi: 10.1007/s00442-010-1568-6. Epub 2010 Feb 4.
The potential role of prey refuges in stabilizing predator-prey interactions is of longstanding interest to ecologists, but mechanisms underlying a sigmoidal predator functional response remain to be fully elucidated. Authors have disagreed on whether the stabilizing effect of prey refuges is driven by prey- versus predator-centric mechanisms, but to date few studies have married predator and prey behavioural observations to distinguish between these possibilities. We used a dragonfly nymph-tadpole system to study the effect of a structural refuge (leaf litter) on the predator's functional response, and paired this with behavioural observations of both predator and prey. Our study confirmed that hyperbolic (type II) functional responses were characteristic of foraging predators when structural cover was low or absent, whereas the functional response was sigmoidal (type III) when prey were provided with sufficient refuge. Prey activity and refuge use were density independent across cover treatments, thereby eliminating a prey-centric mechanism as being the genesis for density-dependent predation. In contrast, the predator's pursuit length, capture success, and handling time were altered by the amount of structure implying that observed shifts in density-dependent predation likely were related to predator hunting efficiency. Our study advances current theory by revealing that despite fixed-proportion refuge use by prey, presence of a prey refuge can induce density-dependent predation through its effect on predator hunting strategy. Ultimately, responses of predator foraging decisions in response to changes in prey availability and search efficiency may be more important in producing density-dependent predation than the form of prey refuge use.
猎物避难所对稳定捕食者-猎物相互作用的潜在作用一直是生态学家感兴趣的话题，但捕食者功能反应的呈“S”型的机制仍有待充分阐明。作者们对猎物避难所的稳定作用是由猎物还是捕食者为中心的机制驱动存在分歧，但迄今为止，很少有研究将捕食者和猎物的行为观察结合起来，以区分这些可能性。我们使用蜻蜓若虫-蝌蚪系统来研究结构避难所（落叶）对捕食者功能反应的影响，并将其与对捕食者和猎物的行为观察相结合。我们的研究证实，当结构覆盖物较低或不存在时，捕食者的功能反应呈双曲线（II 型）特征，而当猎物提供足够的避难所时，功能反应呈“S”型（III 型）。在覆盖物处理方面，猎物的活动和避难所的使用与密度无关，从而消除了以猎物为中心的机制是密度依赖性捕食的起源。相比之下，尽管猎物以固定比例使用避难所，但捕食者的追逐长度、捕获成功率和处理时间会因结构数量的变化而改变，这表明观察到的密度依赖性捕食的变化可能与捕食者的狩猎效率有关。我们的研究通过揭示尽管猎物有固定比例的避难所使用，但猎物避难所的存在可以通过其对捕食者狩猎策略的影响来诱导密度依赖性捕食，从而推进了当前的理论。最终，捕食者觅食决策对猎物可利用性和搜索效率变化的反应可能比猎物避难所使用的形式更重要，从而产生密度依赖性捕食。
