Biology Department, Georgetown University, Washington, D.C., 20057, USA.
Department of Biological Sciences, University of Denver, Denver, Colorado, 80208, USA.
Ecology. 2019 Jun;100(6):e02662. doi: 10.1002/ecy.2662. Epub 2019 Apr 23.
Generalist predators are thought to be less vulnerable to habitat fragmentation because they use diverse resources across larger spatial scales than specialist predators. Thus, it has been suggested that generalist predators may respond positively to habitat edges or demonstrate no edge response, because they can potentially use prey resources equally well on both sides of the habitat edge. However, most predictions about generalist predator responses to the habitat edge are based solely on prey resources, without consideration of other potential drivers. For instance, structural resources are essential for some species to build webs to capture prey or to avoid intraguild predation and cannibalism. In this study, we used both prey and structural resources to predict the response of four predator functional groups (hunting spiders, web-building spiders, aerial predators, and epigeic predators that feed on the detrital/algal food web) to a habitat edge between two salt-marsh grasses (Spartina alterniflora and Spartina patens). We found that generalist predators largely demonstrated negative responses to the habitat edge and had distinct habitat associations. Positive edge responses were only observed in one functional group (hunting spiders), and this pattern was driven by the two most abundant species. Negative responses to the habitat edge were more common among taxa and were better explained by structural resources rather than prey resources in the two habitats. Although it is generally acknowledged that specialists decline in fragmented habitats, generalists are thought to be more resilient. However, our research demonstrates that even generalists have habitat structural or food resource requirements that may limit their resilience to habitat loss and fragmentation.
一般掠食者被认为不太容易受到生境破碎化的影响，因为它们在更大的空间尺度上使用多样化的资源，而不是专门的掠食者。因此，有人认为，一般掠食者可能会对生境边缘产生积极的反应，或者没有边缘反应，因为它们有可能在生境边缘的两侧同样有效地利用猎物资源。然而，大多数关于一般掠食者对生境边缘反应的预测仅仅基于猎物资源，而没有考虑其他潜在的驱动因素。例如，结构资源对于一些物种来说是必不可少的，它们可以用这些资源来建造网来捕捉猎物，或者避免种内捕食和自相残杀。在这项研究中，我们使用猎物和结构资源来预测四个捕食者功能群（捕猎蜘蛛、织网蜘蛛、空中捕食者和以碎屑/藻类食物网为食的地上捕食者）对两种盐沼草（互花米草和大米草）之间的生境边缘的反应。我们发现，一般掠食者对生境边缘表现出很大的负面反应，并且具有明显的生境关联。只有一个功能群（捕猎蜘蛛）表现出积极的边缘反应，这种模式是由两种最丰富的物种驱动的。对生境边缘的负面反应在分类群中更为常见，并且在两个栖息地中，结构资源比猎物资源更好地解释了这种反应。虽然人们普遍认为，专门化物种在破碎化的生境中减少，但一般认为，一般化物种更有弹性。然而，我们的研究表明，即使是一般化物种也有生境结构或食物资源的需求，这可能限制它们对生境丧失和破碎化的适应能力。
