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Abstract：
Human activities degrade and fragment coastal marine habitats, reducing their structural complexity and making habitat edges a prevalent seascape feature. Though habitat edges frequently are implicated in reduced faunal survival and biodiversity, results of experiments on edge effects have been inconsistent, calling for a mechanistic approach to the study of edges that explicitly includes indirect and interactive effects of habitat alteration at multiple scales across biogeographic gradients. We used an experimental network spanning 17 eelgrass (Zostera marina) sites across the Atlantic and Pacific oceans and the Mediterranean Sea to determine (1) if eelgrass edges consistently increase faunal predation risk, (2) whether edge effects on predation risk are altered by habitat degradation (shoot thinning), and (3) whether variation in the strength of edge effects among sites can be explained by biogeographical variability in covarying eelgrass habitat features. Contrary to expectations, at most sites, predation risk for tethered crustaceans (crabs or shrimps) was lower along patch edges than in patch interiors, regardless of the extent of habitat degradation. However, the extent to which edges reduced predation risk, compared to the patch interior, was correlated with the extent to which edges supported higher eelgrass structural complexity and prey biomass compared to patch interiors. This suggests an indirect component to edge effects in which the impact of edge proximity on predation risk is mediated by the effect of edges on other key biotic factors. Our results suggest that studies on edge effects should consider structural characteristics of patch edges, which may vary geographically, and multiple ways that humans degrade habitats.
摘要：
人类活动退化和破坏沿海海洋栖息地，减少其结构复杂性，并使栖息地边缘成为普遍的海景特征。尽管栖息地边缘经常与动物生存和生物多样性的减少有关，关于边缘效应的实验结果不一致，呼吁采用机械方法来研究边缘，明确地包括跨生物地理梯度的多个尺度上的栖息地改变的间接和交互影响。我们使用了一个横跨大西洋和太平洋以及地中海的17个鳗草（Zosteramarina）站点的实验网络，以确定（1）鳗草边缘是否持续增加动物捕食风险，(2)栖息地退化(枝条变薄)是否改变了捕食风险的边缘效应，（3）站点之间边缘效应强度的变化是否可以通过协变eelgrass生境特征的生物地理变异性来解释。与预期相反,在大多数网站，系留甲壳类动物（螃蟹或虾）的捕食风险沿斑块边缘低于斑块内部，无论栖息地退化的程度如何。然而,边缘降低捕食风险的程度，与贴片内部相比，与斑块内部相比，边缘支持更高的鳗草结构复杂性和猎物生物量的程度相关。这表明边缘效应的间接组成部分，其中边缘接近对捕食风险的影响是由边缘对其他关键生物因素的影响介导的。我们的结果表明，对边缘效应的研究应考虑斑块边缘的结构特征，可能在地理上有所不同，以及人类退化栖息地的多种方式。
