School of Forest Resources, University of Washington, Box 352100, Seattle, WA, 98103, USA.
Oecologia. 2012 Apr;168(4):977-88. doi: 10.1007/s00442-011-2158-y. Epub 2011 Oct 19.
There has long been interest in the influence of predators on prey populations, although most predator-prey studies have focused on prey species that are targets of directed predator searching. Conversely, few have addressed depredation that occurs after incidental encounters with predators. We tested two predictions stemming from the hypothesis that nest predation on two sympatric freshwater turtle species whose nests are differentially prone to opportunistic detection-painted turtles (Chrysemys picta) and snapping turtles (Chelydra serpentina)-is incidental: (1) predation rates should be density independent, and (2) individual predators should not alter their foraging behavior after encountering nests. After monitoring nest survival and predator behavior following nest depredation over 2 years, we confirmed that predation by raccoons (Procyon lotor), the primary nest predators in our study area, matched both predictions. Furthermore, cryptic C. picta nests were victimized with lower frequency than more detectable C. serpentina nests, and nests of both species were more vulnerable in human-modified areas where opportunistic nest discovery is facilitated. Despite apparently being incidental, predation on nests of both species was intensive (57% for painted turtles, 84% for snapping turtles), and most depredations occurred within 1 day of nest establishment. By implication, predation need not be directed to affect prey demography, and factors influencing prey crypsis are drivers of the impact of incidental predation on prey. Our results also imply that efforts to conserve imperiled turtle populations in human-modified landscapes should include restoration of undisturbed conditions that are less likely to expose nests to incidental predators.
长期以来，人们一直关注捕食者对猎物种群的影响，尽管大多数捕食者-猎物研究都集中在那些成为定向捕食者搜索目标的猎物物种上。相反，很少有研究涉及到与捕食者偶然相遇后发生的捕食行为。我们测试了两个源于以下假设的预测：即在两种同域淡水龟中，巢捕食发生在偶然相遇之后，而这两种龟的巢分别更容易被机会主义探测到——彩龟（Chrysemys picta）和蛇颈龟（Chelydra serpentina）——这是偶然的：（1）捕食率应该与密度无关，（2）个体捕食者在遇到巢后不应改变其觅食行为。在监测巢存活率和捕食者行为后，我们确认了在 2 年的巢捕食后，浣熊（Procyon lotor）作为我们研究区域的主要巢捕食者，符合这两个预测。此外，与更易察觉的 C. serpentina 巢相比，隐蔽的 C. picta 巢受害频率较低，而两种物种的巢在人为干扰的地区更容易受到机会主义的巢发现的影响，因此更容易受到影响。尽管捕食似乎是偶然的，但对两种物种的巢的捕食都是密集的（彩龟 57%，蛇颈龟 84%），并且大多数捕食行为都发生在巢建立后的 1 天内。因此，捕食不必是定向的，也会影响猎物的种群动态，而影响猎物隐蔽性的因素是偶然捕食对猎物的影响的驱动因素。我们的研究结果还表明，在人为干扰的景观中保护濒危龟类种群的努力，应该包括恢复那些不太可能将巢穴暴露给偶然捕食者的未受干扰的条件。
