Although parasites represent an important component of ecosystems, few field and theoretical studies have addressed the structure of parasites in food webs. We evaluate the structure of parasitic links in an extensive salt marsh food web, with a new model distinguishing parasitic links from non-parasitic links among free-living species. The proposed model is an extension of the niche model for food web structure, motivated by the potential role of size (and related metabolic rates) in structuring food webs. The proposed extension captures several properties observed in the data, including patterns of clustering and nestedness, better than does a random model. By relaxing specific assumptions, we demonstrate that two essential elements of the proposed model are the similarity of a parasite’s hosts and the increasing degree of parasite specialization, along a one-dimensional niche axis. Thus, inverting one of the basic rules of the original model, the one determining consumers’ generality appears critical. Our results support the role of size as one of the organizing principles underlying niche space and food web topology. They also strengthen the evidence for the non-random structure of parasitic links in food webs and open the door to addressing questions concerning the consequences and origins of this structure.

中文翻译：

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带有寄生虫的食物网的逆生境模型。

尽管寄生虫是生态系统的重要组成部分，但很少有田野和理论研究针对食物网中的寄生虫结构进行研究。我们评估了一个广泛的盐沼食物网中寄生链接的结构，并建立了一个新模型来区分寄生链接和自由生活物种之间的非寄生链接。所提出的模型是食物网结构利基模型的扩展，受尺寸（和相关代谢率）在构造食物网中的潜在作用所驱动。与随机模型相比，拟议的扩展捕获了数据中观察到的多个属性，包括聚类和嵌套模式。通过放宽特定假设，我们证明了所提出模型的两个基本要素是寄生虫宿主的相似性和沿着一维利基轴的寄生虫专化程度的提高。因此，颠倒原始模型的基本规则之一，决定消费者普遍性的规则就显得至关重要。我们的研究结果支持了尺寸作为利基空间和食物网拓扑结构背后的组织原则之一的作用。他们还加强了食物网中寄生链接的非随机结构的证据，并为解决有关这种结构的后果和起源的问题打开了大门。我们的研究结果支持了尺寸作为利基空间和食物网拓扑结构背后的组织原则之一的作用。他们还加强了食物网中寄生链接的非随机结构的证据，并为解决有关这种结构的后果和起源的问题打开了大门。我们的研究结果支持了尺寸作为利基空间和食物网拓扑结构背后的组织原则之一的作用。他们还加强了食物网中寄生链接的非随机结构的证据，并为解决有关这种结构的后果和起源的问题打开了大门。