Mouillot David, Krasnov Boris R, Poulin Robert
UMR CNRS-UM2-IFREMER 5119 Ecosystemes Lagunaires, University of Montpellier 2, CC093, 34095 Montpellier, Cedex 5, France.
Ecology. 2008 Jul;89(7):2043-51. doi: 10.1890/07-1241.1.
The finding of invariant structures in species interaction webs is of central importance for ecology, with the greatest challenge remaining the elucidation of the processes governing these universal web patterns. Here we quantify the degree of intervality of seven fish-metazoan and 33 mammal-flea webs, i.e., the number of irreducible gaps in parasite diets along the host spectrum, and then challenge the idea that some invariant structures may emerge in host-parasite webs. Using a null model of random links between parasite and host species we find that empirical host-parasite webs exhibit a strong bias toward contiguity of parasite diet, i.e., toward intervality. Going one step further, we demonstrate that a null model with phylogenetic constraints on host-parasite links produced webs very similar to empirical ones, particularly when phylogenetic constraints occur at the family level, that is, when two hosts from the same family are more likely to be infected than two random hosts. In addition, we propose a new standardized measure of intervality which describes a novel "facet" of natural networks as it is independent of connectance or web size. We suggest using this measure as a surrogate of web maturity or saturation as phylogenetic constraints can drive webs toward intervality.
在物种相互作用网络中发现不变结构对生态学至关重要，而最大的挑战仍然是阐明支配这些普遍网络模式的过程。在这里，我们量化了七个鱼类 - 后生动物网络和33个哺乳动物 - 跳蚤网络的间隔程度，即寄生虫饮食沿宿主谱系中不可约间隙的数量，然后对宿主 - 寄生虫网络中可能出现一些不变结构的观点提出质疑。使用寄生虫和宿主物种之间随机链接的零模型，我们发现经验性宿主 - 寄生虫网络对寄生虫饮食的连续性表现出强烈偏向，即对间隔性的偏向。更进一步，我们证明了对宿主 - 寄生虫链接施加系统发育约束的零模型产生的网络与经验网络非常相似，特别是当系统发育约束发生在科级水平时，也就是说，来自同一家族的两个宿主比两个随机宿主更有可能被感染。此外，我们提出了一种新的间隔性标准化度量，它描述了自然网络的一个新“方面”，因为它独立于连通性或网络大小。我们建议使用这种度量作为网络成熟度或饱和度的替代指标，因为系统发育约束可以使网络趋向于间隔性。
