Queen's University Belfast, Belfast BT9 7BL, UK.
Proc Biol Sci. 2011 Jun 7;278(1712):1617-25. doi: 10.1098/rspb.2010.1483. Epub 2010 Nov 10.
A central question in community ecology is how the number of trophic links relates to community species richness. For simple dynamical food-web models, link density (the ratio of links to species) is bounded from above as the number of species increases; but empirical data suggest that it increases without bounds. We found a new empirical upper bound on link density in large marine communities with emphasis on fish and squid, using novel methods that avoid known sources of bias in traditional approaches. Bounds are expressed in terms of the diet-partitioning function (DPF): the average number of resources contributing more than a fraction f to a consumer's diet, as a function of f. All observed DPF follow a functional form closely related to a power law, with power-law exponents independent of species richness at the measurement accuracy. Results imply universal upper bounds on link density across the oceans. However, the inherently scale-free nature of power-law diet partitioning suggests that the DPF itself is a better defined characterization of network structure than link density.
一个中心问题在群落生态学是如何营养链接的数量与社区物种丰富度有关。对于简单的动力食物网模型，链接密度（链接与物种的比例）是有界的，随着物种数量的增加;但经验数据表明，它是无界的。我们发现了一个新的经验上限的链接密度在大型海洋社区的重点是鱼类和鱿鱼，使用新的方法，避免了在传统方法中的已知来源的偏差。界限表示在饮食分割函数（DPF）：平均数量的资源贡献超过了消费者的饮食，作为一个函数的 f 分数。所有观察到的 DPF 遵循一个密切相关的功能形式的幂律，幂律指数与物种丰富度在测量精度上是独立的。结果表明，海洋中普遍存在着链接密度的上限。然而，幂律饮食分割的固有无标度性质表明，DPF 本身是网络结构的一个更好的定义特征，而不是链接密度。
