Texas A&M University, Department of Life Sciences, 6300 Ocean Drive, Unit 5800, Corpus Christi, Texas 78412, USA.
Ecology. 2010 May;91(5):1391-400. doi: 10.1890/09-0017.1.
Predators often have large effects on community structure, but these effects can be minimized in habitats subjected to intense physical stress. For example, predators exert large effects on rocky intertidal communities on wave-protected shores but are usually absent from wave-swept shores where hydrodynamic forces prevent them from foraging effectively. The physical environment also can affect predation levels when stressors are not severe enough to be physically risky. In these situations, environmental conditions may constrain a predator's ability to locate prey and alleviate predation pressure. Yet, stress models of community structure have rarely considered the implications of such sensory or behavioral stressors, particularly when the sensory abilities of both predators and prey are affected by the same types of environmental conditions. Ecologists may classify certain environmental conditions as refuges if they impede predator foraging, but these conditions may not actually decrease predation levels if they simultaneously increase prey vulnerability to consumers. Using blue crabs (Callinectes sapidus) and hard clams (Mercenaria mercenaria) as a model system, we investigated the relationship between predation intensity and environmental stress in the form of hydrodynamics (i.e., flow velocity and turbulence). Blue crabs and hard clams are less responsive to each other in faster, more turbulent flows, but studies exploring how flow modulates the outcomes of crab-clam interactions in the field are lacking. We manipulated turbulence within field sites and compared predation levels within and between sites that differed in flow velocity and turbulence. Our results suggest that blue crabs are most effective foragers in flows with intermediate velocities and turbulence levels. Although these conditions are not ideal for blue crabs, lab studies indicate that they also compromise the ability of clams to detect and react to approaching crabs and, thereby, increase clam vulnerability to predators. Our results suggest that environmental stresses on perception (sensory stressors) may not cause a steady decay in predation rates when they simultaneously affect the behaviors of both predators and prey. Moreover, the relative contribution of lethal vs. nonlethal predator effects in communities also may be influenced by environmental forces that enhance the predator-avoidance abilities of prey or the foraging efficiency of predators.
捕食者通常对群落结构有很大的影响，但在受到强烈物理压力的生境中，这些影响可以最小化。例如，在受波浪保护的海岸上的岩石潮间带群落中，捕食者会产生很大的影响，但在波浪冲刷的海岸上，由于水动力阻止它们有效地觅食，捕食者通常不存在。当压力源不足以造成身体风险时，物理环境也会影响捕食水平。在这些情况下，环境条件可能会限制捕食者寻找猎物的能力，并减轻捕食压力。然而，群落结构的应激模型很少考虑到这种感官或行为应激源的影响，特别是当捕食者和猎物的感官能力都受到相同类型的环境条件影响时。生态学家如果捕食者的觅食受到阻碍，可能会将某些环境条件归类为避难所，但如果这些条件同时增加了猎物对消费者的脆弱性，它们实际上并不会降低捕食水平。我们使用蓝蟹（Callinectes sapidus）和硬壳蛤（Mercenaria mercenaria）作为模型系统，研究了捕食强度与水动力（即流速和湍流）形式的环境压力之间的关系。在更快、更湍流的水流中，蓝蟹和硬壳蛤对彼此的反应较小，但缺乏研究探索水流如何调节现场蟹蛤相互作用的结果。我们在现场站点内操纵湍流，并比较了流速和湍流不同的站点内和站点间的捕食水平。我们的结果表明，蓝蟹在流速和湍流水平中等的水流中是最有效的觅食者。尽管这些条件对蓝蟹不利，但实验室研究表明，它们也会损害蛤类检测和对接近的蟹类做出反应的能力，从而增加蛤类对捕食者的脆弱性。我们的结果表明，当环境对感知的压力（感官压力源）同时影响捕食者和猎物的行为时，它们可能不会导致捕食率的稳定下降。此外，增强猎物逃避捕食者能力或捕食者觅食效率的环境力量也可能影响社区中致死与非致死捕食者效应的相对贡献。
