Data from: Effects of spatial scale of sampling on food web structure

This study asks whether the spatial scale of sampling alters structural properties of food webs and whether any differences are attributable to changes in species richness and connectance with scale. Understanding how different aspects of sampling effort affect ecological network structure is important for both fundamental ecological knowledge and the application of network analysis in conservation and management. Using a highly resolved food web for the marine intertidal ecosystem of the Sanak Archipelago in the Eastern Aleutian Islands, Alaska, we assess how commonly studied properties of network structure differ for 281 versions of the food web sampled at five levels of spatial scale representing six orders of magnitude in area spread across the archipelago. Species (S) and link (L) richness both increased by approximately one order of magnitude across the five spatial scales. Links per species (L/S) more than doubled, while connectance (C) decreased by approximately two-thirds. Fourteen commonly studied properties of network structure varied systematically with spatial scale of sampling, some increasing and others decreasing. While ecological network properties varied systematically with sampling extent, analyses using the niche model and a power-law scaling relationship indicate that for many properties, this apparent sensitivity is attributable to the increasing S and decreasing C of webs with increasing spatial scale. As long as effects of S and C are accounted for, areal sampling bias does not have a special impact on our understanding of many aspects of network structure. However, attention does need be paid to some properties such as the fraction of species in loops, which increases more than expected with greater spatial scales of sampling.本研究旨在探究两个核心问题：采样的空间尺度是否会改变食物网（food web）的结构属性，以及此类结构差异是否可归因于物种丰富度（species richness）与连接度（connectance）随空间尺度发生的变化。明晰采样投入（sampling effort）的不同维度如何影响生态网络（ecological network）结构，无论是对于基础生态学研究，还是将网络分析（network analysis）应用于保护与管理实践均具有重要意义。 本研究以阿拉斯加州阿留申群岛东部萨纳克群岛（Sanak Archipelago）潮间带海洋生态系统的高分辨率食物网（highly resolved food web）为研究对象，针对覆盖该群岛面积跨越6个数量级的5级空间尺度（spatial scale），构建了281个经采样得到的食物网版本，并评估了常见网络结构属性在这些版本间的差异。 在5个空间尺度下，物种丰富度（S）与连接丰富度（L）均提升了约一个数量级；每物种连接数（L/S）提升了一倍以上，而连接度（C）则下降了约三分之二。14种常见网络结构属性均随采样空间尺度呈现系统性变化，部分属性随尺度扩大而升高，部分则随之降低。 尽管生态网络属性随采样范围呈现系统性变化，但借助生态位模型（niche model）与幂律缩放关系（power-law scaling relationship）开展的分析表明，对于多数属性而言，这种表观敏感性可归因于随着空间尺度扩大，食物网的物种丰富度不断提升而连接度持续下降。只要将物种丰富度与连接度的影响纳入考量，区域采样偏差（areal sampling bias）并不会对我们理解多数网络结构维度产生特殊干扰。 但仍需关注部分特殊属性，例如食物网环内物种占比（fraction of species in loops），其随采样空间尺度扩大的增幅超出预期。