Rudolf Volker H W
Department of Ecology and Evolutionary Biology, Rice University, Houston, TX 77005, USA.
Ecology. 2008 Jun;89(6):1650-60. doi: 10.1890/07-0709.1.
Direct and indirect interactions between two prey species can strongly alter the dynamics of predator-prey systems. Most predators are cannibalistic, and as a consequence, even systems with only one predator and one prey include two prey types: conspecifics and heterospecifics. The effects of the complex direct and indirect interactions that emerge in such cannibalistic systems are still poorly understood. This study examined how the indirect interaction between conspecific and heterospecific prey affects cannibalism and predation rates and how the direct interactions between both species indirectly alter the effect of the cannibalistic predator. I tested for these effects using larvae of the stream salamanders Eurycea cirrigera (prey) and Pseudotriton ruber (cannibalistic predator) by manipulating the relative densities of the conspecific and heterospecific prey in the presence and absence of the predator in experimental streams. The rates of cannibalism and heterospecific predation were proportional to the respective densities and negatively correlated, indicating a positive indirect interaction between conspecific and heterospecific prey, similar to "apparent mutualism." Direct interactions between prey species did not alter the effect of the predator. Although both types of prey showed a similar 30% reduction in night activity and switch in microhabitat use in response to the presence of the predator, cannibalism rates were three times higher than heterospecific predation rates irrespective of the relative densities of the two types of prey. Cumulative predation risks differed even more due to the 48% lower growth rate of conspecific prey. Detailed laboratory experiments suggest that the 3:1 difference in cannibalism and predation rate was due to the higher efficiency of heterospecific prey in escaping immediate attacks. However, no difference was observed when the predator was a closely related salamander species, Gyrinophilus porphyriticus, indicating that this difference is species specific. This demonstrates that cannibalism can result in the coupling of predator and prey mortality rates that strongly determines the dynamics of predator-prey systems.
两种猎物物种之间的直接和间接相互作用能够强烈改变捕食者 - 猎物系统的动态。大多数捕食者具有同类相食的习性，因此，即使是只有一种捕食者和一种猎物的系统也包含两种猎物类型：同种个体和异种个体。在这种同类相食的系统中出现的复杂直接和间接相互作用的影响仍然知之甚少。本研究考察了同种猎物和异种猎物之间的间接相互作用如何影响同类相食率和捕食率，以及这两种猎物之间的直接相互作用如何间接改变同类相食性捕食者的效应。我通过在实验溪流中，在有捕食者和无捕食者的情况下，操纵同种猎物和异种猎物的相对密度，使用溪流蝾螈Eurycea cirrigera（猎物）和Pseudotriton ruber（同类相食性捕食者）的幼体来测试这些效应。同类相食率和异种捕食率与各自的密度成正比且呈负相关，表明同种猎物和异种猎物之间存在正的间接相互作用，类似于“表观互利共生”。猎物物种之间的直接相互作用并未改变捕食者的效应。尽管两种猎物在捕食者存在时夜间活动都有类似30%的减少，并且微生境使用发生转变，但无论两种猎物的相对密度如何，同类相食率都比异种捕食率高三倍。由于同种猎物的生长速率低48%，累积捕食风险差异更大。详细的实验室实验表明，同类相食率和捕食率3:1的差异是由于异种猎物在躲避即时攻击方面效率更高。然而，当捕食者是亲缘关系密切的蝾螈物种Gyrinophilus porphyriticus时，未观察到差异，这表明这种差异具有物种特异性。这表明同类相食会导致捕食者和猎物死亡率的耦合，这强烈决定了捕食者 - 猎物系统的动态。
