Department of Biology, Trent University, Peterborough, Ontario, K9J 7B8, Canada.
Department of Biological Sciences, University of Alberta, Edmonton, Alberta, T6G 2E9, Canada.
Ecology. 2017 Jul;98(7):1787-1796. doi: 10.1002/ecy.1828. Epub 2017 Jun 12.
To improve understanding of the complex and variable patterns of predator foraging behavior in natural systems, it is critical to determine how density-dependent predation and predator hunting success are mediated by alternate prey or predator interference. Despite considerable theory and debate seeking to place predator-prey interactions in a more realistic context, few empirical studies have quantified the role of alternate prey or intraspecific interactions on predator-prey dynamics. We assessed functional responses of two similarly sized, sympatric carnivores, lynx (Lynx canadensis) and coyotes (Canis latrans), foraging on common primary (snowshoe hares; Lepus americanus) and alternate (red squirrels; Tamiasciurus hudsonicus) prey in a natural system. Lynx exhibited a hyperbolic prey-dependent response to changes in hare density, which is characteristic of predators relying primarily on a single prey species. In contrast, the lynx-squirrel response was found to be linear ratio dependent, or inversely dependent on hare density. The coyote-hare and coyote-squirrel interactions also were linear and influenced by predator density. We explain these novel results by apparent use of spatial and temporal refuges by prey, and the likelihood that predators commonly experience interference and lack of satiation when foraging. Our study provides empirical support from a natural predator-prey system that (1) predation rate may not be limited at high prey densities when prey are small or rarely captured; (2) interference competition may influence the predator functional response; and (3) predator interference has a variable role across different prey types. Ultimately, distinct functional responses of predators to different prey types illustrates the complexity associated with predator-prey interactions in natural systems and highlights the need to investigate predator behavior and predation rate in relation to the broader ecological community.
为了更好地理解自然系统中捕食者觅食行为的复杂多变模式，关键是要确定密度依赖型捕食和捕食者狩猎成功率是如何受到替代猎物或捕食者干扰的影响。尽管有大量的理论和争论试图将捕食者-猎物相互作用置于更现实的背景下，但很少有实证研究量化替代猎物或种内相互作用对捕食者-猎物动态的作用。我们评估了两种体型相似、同域的食肉动物——猞猁（Lynx canadensis）和郊狼（Canis latrans）——在自然系统中捕食常见的主要猎物（雪兔；Lepus americanus）和替代猎物（红松鼠；Tamiasciurus hudsonicus）时的功能反应。猞猁对雪兔密度变化的依赖呈双曲线反应，这是依赖单一猎物物种的捕食者的典型特征。相比之下，猞猁-松鼠的反应是线性比例依赖的，或者与雪兔密度呈反比。郊狼-野兔和郊狼-松鼠的相互作用也是线性的，并受到捕食者密度的影响。我们通过猎物明显使用空间和时间避难所以及捕食者在觅食时经常遇到干扰和没有饱腹感的可能性来解释这些新的结果。我们的研究从自然捕食者-猎物系统中提供了实证支持，即（1）当猎物较小时或很少被捕食时，捕食率在高猎物密度下可能不受限制；（2）干扰竞争可能会影响捕食者的功能反应；（3）捕食者干扰在不同猎物类型中具有可变的作用。最终，捕食者对不同猎物类型的不同功能反应说明了自然系统中捕食者-猎物相互作用的复杂性，并强调了需要调查捕食者行为和捕食率与更广泛的生态群落的关系。
