Parasites affect food web structure primarily through increased diversity and complexity.
Parasites affect food web structure primarily through increased diversity and complexity.
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DOI：
10.1371/journal.pbio.1001579
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发表时间：
2013
期刊：
影响因子：
9.8
通讯作者：
Zander CD
中科院分区：
文献类型：
--
作者：
Dunne JA;Lafferty KD;Dobson AP;Hechinger RF;Kuris AM;Martinez ND;McLaughlin JP;Mouritsen KN;Poulin R;Reise K;Stouffer DB;Thieltges DW;Williams RJ;Zander CD
寄生虫主要通过改变多样性和复杂性来影响食物网结构。然而，与自由生活的物种相比，它们的生活史特征导致更复杂的摄食生态位和改变的图案。对食物网结构的比较研究揭示了营养组织的共性，产生了简单的模型，并允许评估物种损失的鲁棒性。这些研究主要集中在自由生活的物种。最近的研究表明，包含寄生虫会改变结构。我们评估这种网络结构的变化是否是由寄生虫的独特作用和特征引起的，或者是由多样性和复杂性的变化引起的。我们分析了七个高分辨率的食物网，包括后生动物寄生虫的数据。我们的分析表明，添加寄生虫通常会增加链接密度和连通性（复杂性的简单措施），特别是当包括伴随链接（从捕食者到其猎物的寄生虫的链接）。然而，我们澄清了先前的说法，寄生虫“主宰”食物网链接。虽然寄生虫可以参与大多数环节，在大多数情况下，经典的捕食环节超过经典的寄生环节。关于网络结构，观察到的度分布变化，14个常用的研究指标，和链接概率是一致的规模相关的结构变化与多样性和复杂性的变化。因此，寄生虫和自由生活的物种对结构的这些方面具有类似的影响。然而，有两个变化表明了寄生虫的独特作用。首先，添加寄生虫和伴随的链接强烈改变了三个类群之间的相互作用的大多数图案的频率，反映了寄生虫作为其宿主的捕食者的资源的角色，由与宿主的营养亲密度驱动。第二，与自由生活的消费者相比，许多寄生虫的摄食生态位看起来更宽，更不连续，这可能反映了复杂的生命周期和较小的体型。这项研究提供了新的见解一般与独特的影响，寄生虫对食物网结构，扩展了食物网理论的一般性，给出了一个更严格的框架，评估任何物种对营养组织的影响，确定目前的食物网模型的局限性，并为未来的结构和动力学模型提供了方向。食物网是物种之间相互捕食的网络。虽然寄生虫在物种多样性中占很大比例，但它们在食物网数据和分析中的代表性通常不足。之前对包含寄生虫的少数数据集的分析表明，它们的包含改变了网络结构。然而，目前还不清楚这些变化是寄生虫发挥的独特作用的结果，还是由于任何类型的物种加入食物网时会发生的多样性和复杂性的变化。在这项研究中，我们分析了七个高分辨率的沿海河口或海洋寄生虫食物网的网络结构的许多方面。在大多数情况下，我们发现，在分析中包括寄生虫会导致食物网结构的一般变化，这将是预期的增加多样性和复杂性。然而，就食物网中特定的链接模式（“图案”）和摄食生态位的宽度和连续性而言，寄生虫确实会以独特的特征改变结构，特别是它们与宿主的亲密身体关系，复杂的生命周期和较小的体型。因此，这项研究解开独特的寄生虫对食物网组织的一般影响，提供更好地了解寄生虫和自由生活的物种在其作为消费者和资源的角色之间的相似性和差异。
Parasites primarily affect food web structure through changes to diversity and complexity. However, compared to free-living species, their life-history traits lead to more complex feeding niches and altered motifs. Comparative research on food web structure has revealed generalities in trophic organization, produced simple models, and allowed assessment of robustness to species loss. These studies have mostly focused on free-living species. Recent research has suggested that inclusion of parasites alters structure. We assess whether such changes in network structure result from unique roles and traits of parasites or from changes to diversity and complexity. We analyzed seven highly resolved food webs that include metazoan parasite data. Our analyses show that adding parasites usually increases link density and connectance (simple measures of complexity), particularly when including concomitant links (links from predators to parasites of their prey). However, we clarify prior claims that parasites “dominate” food web links. Although parasites can be involved in a majority of links, in most cases classic predation links outnumber classic parasitism links. Regarding network structure, observed changes in degree distributions, 14 commonly studied metrics, and link probabilities are consistent with scale-dependent changes in structure associated with changes in diversity and complexity. Parasite and free-living species thus have similar effects on these aspects of structure. However, two changes point to unique roles of parasites. First, adding parasites and concomitant links strongly alters the frequency of most motifs of interactions among three taxa, reflecting parasites' roles as resources for predators of their hosts, driven by trophic intimacy with their hosts. Second, compared to free-living consumers, many parasites' feeding niches appear broader and less contiguous, which may reflect complex life cycles and small body sizes. This study provides new insights about generic versus unique impacts of parasites on food web structure, extends the generality of food web theory, gives a more rigorous framework for assessing the impact of any species on trophic organization, identifies limitations of current food web models, and provides direction for future structural and dynamical models. Food webs are networks of feeding interactions among species. Although parasites comprise a large proportion of species diversity, they have generally been underrepresented in food web data and analyses. Previous analyses of the few datasets that contain parasites have indicated that their inclusion alters network structure. However, it is unclear whether those alterations were a result of unique roles that parasites play, or resulted from the changes in diversity and complexity that would happen when any type of species is added to a food web. In this study, we analyzed many aspects of the network structure of seven highly resolved coastal estuary or marine food webs with parasites. In most cases, we found that including parasites in the analysis results in generic changes to food web structure that would be expected with increased diversity and complexity. However, in terms of specific patterns of links in the food web (“motifs”) and the breadth and contiguity of feeding niches, parasites do appear to alter structure in ways that result from unique traits—in particular, their close physical intimacy with their hosts, their complex life cycles, and their small body sizes. Thus, this study disentangles unique from generic effects of parasites on food web organization, providing better understanding of similarities and differences between parasites and free-living species in their roles as consumers and resources.
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