水生生态系统食物网复杂性与多样性的关系

探索食物网的复杂结构是生态学的中心问题之一。基于构建的黄河口海草床食物网并耦合实际食物网的数据集,整理了包含河口、湖泊、海洋和河流四种水生生态系统类型的48个实际食物网案例。以食物网的节点数反映食物网多样性,物种之间的营养链接数、链接密度和连通度来表示食物网的复杂性,采用营养缩尺模型描述水生生态系统食物网的复杂性特征与节点数的普适性规律。结果表明：所涉及的48个水生生态系统食物网的多样性和复杂性跨度较大,其中,节点数的分布范围为4-124,链接数为3-1830,链接密度为0.75-15.71,连通度为0.06-0.25。不同类型水生生态系统间的连通度存在显著性差异（P=0.01）,节点数、链接数、链接密度不存在显著性差异。各类型生态系统的食物网链接数、链接密度均随节点数的增加而增加（R²=0.92,P<0.001和R²=0.82,P<0.001）。湖泊生态系统的连通度随节点数的变化不明显,围绕在0.20附近;而其他3种类型生态系统的食物网连通度随节点数的增加而降低（R²=0.06-0.41,P<0.001）。对全球尺度的水生食物网多样性和复杂性的定量化研究对于提升对食物网的复杂结构的科学认识,从系统尺度探究多样性和复杂性的关系提供数据支撑。

Relationship between complexity and diversity in aquatic food webs

Food webs are at the heart of understanding the biological structure and functioning of ecosystems. Exploring the complex structure of food webs is one of the central issues in ecological studies. Previous studies have developed two hypotheses, i.e. link-species scaling law and constant connectance. The link-species scaling law assumes that food webs with varying diversity have the same linkage density. The constant connectance hypothesis states that food webs have constant connectance though their diversity varies. Given the inconsistency between the two hypotheses, it is critical to explore the correlation between food web complexity and diversity. Based on the constructed food web structure of a seagrass bed in the Yellow River Estuary and a well-studied actual food web dataset "TroModels", we totally collected 48 food web cases comprising estuarine, lacustrine, marine, and riverine aquatic ecosystems. In this study, the food web complexity was represented by three metrics, i.e. the number of links, linkage density, and connectance, and the number of nodes in the food web indicated its diversity. We used the trophic scaling model to describe the relationships between food web diversity and complexity in various aquatic ecosystems. Our results showed that the food web diversity and complexity of the 48 aquatic food webs varied, in which the number of nodes ranged from 4 to 124, the number of links ranged from 3 to 1830, the linkage density ranged from 0.75 to 15.71, and the connectance ranged from 0.06 to 0.25. The food web connectance differed significantly among different aquatic ecosystems (P=0.01), but there were no significant differences in the number of nodes, the number of links, and the linkage density of food webs among different aquatic ecosystems. Both of the number of links and the linkage density increased with the increasing of the number of nodes (R²=0.92, P<0.001 and R²=0.82, P<0.001, respectively), and there were no obvious correlations among different aquatic ecosystems. In addition, the food web connectance decreased with the increasing of the number of nodes (R²=0.06-0.41, P<0.001) except that the connectance of the lacustrine food webs showed nearly constant value (about 0.20) with the increasing of number of nodes. The quantitative analysis of aquatic food webs on a global scale in terms of food web diversity and complexity provides support for scientific understanding of the complex structure of food webs and the exploration of the relationship between diversity and complexity at the system scale.