Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, 1156 High Street, Santa Cruz, CA 95064, USA.
J R Soc Interface. 2012 Dec 7;9(77):3219-28. doi: 10.1098/rsif.2012.0481. Epub 2012 Jul 25.
Patterns of species interactions affect the dynamics of food webs. An important component of species interactions that is rarely considered with respect to food webs is the strengths of interactions, which may affect both structure and dynamics. In natural systems, these strengths are variable, and can be quantified as probability distributions. We examined how variation in strengths of interactions can be described hierarchically, and how this variation impacts the structure of species interactions in predator-prey networks, both of which are important components of ecological food webs. The stable isotope ratios of predator and prey species may be particularly useful for quantifying this variability, and we show how these data can be used to build probabilistic predator-prey networks. Moreover, the distribution of variation in strengths among interactions can be estimated from a limited number of observations. This distribution informs network structure, especially the key role of dietary specialization, which may be useful for predicting structural properties in systems that are difficult to observe. Finally, using three mammalian predator-prey networks (two African and one Canadian) quantified from stable isotope data, we show that exclusion of link-strength variability results in biased estimates of nestedness and modularity within food webs, whereas the inclusion of body size constraints only marginally increases the predictive accuracy of the isotope-based network. We find that modularity is the consequence of strong link-strengths in both African systems, while nestedness is not significantly present in any of the three predator-prey networks.
物种相互作用模式影响食物网的动态。食物网很少考虑物种相互作用的一个重要组成部分是相互作用的强度，它可能会影响结构和动态。在自然系统中，这些强度是可变的，可以用概率分布来量化。我们研究了如何分层描述相互作用强度的变化，以及这种变化如何影响捕食者-猎物网络中物种相互作用的结构，这两者都是生态食物网的重要组成部分。捕食者和猎物物种的稳定同位素比率可能特别有助于量化这种可变性，我们展示了如何使用这些数据构建概率捕食者-猎物网络。此外，还可以从有限数量的观察中估计相互作用之间强度变化的分布。这种分布可以反映网络结构，特别是饮食专业化的关键作用，这可能有助于预测难以观察的系统中的结构特性。最后，我们使用从稳定同位素数据中量化的三个哺乳动物捕食者-猎物网络（两个非洲网络和一个加拿大网络），表明排除链接强度变异性会导致食物网中嵌套性和模块性的有偏差估计，而包含体型约束仅略微提高了基于同位素的网络的预测准确性。我们发现，在两个非洲系统中，模块性是强链接强度的结果，而嵌套性在三个捕食者-猎物网络中都不存在。
