Neubert M G, Blumenshine S C, Duplisea D E, Jonsson T, Rashleigh B
Biology Department, MS #34, Woods Hole Oceanographic Institution, Woods Hole, MA 02543-1049, USA e-mail:
Department of Biological Sciences, Arkansas State University, State University, AR 72467, USA, , , , , , US.
Oecologia. 2000 May;123(2):241-251. doi: 10.1007/s004420051011.
The cascade model successfuly predicts many patterns in reported food webs. A key assumption of this model is the existence of a predetermined trophic hierarchy; prey are always lower in the hierarchy than their predators. At least three studies have suggested that, in animal food webs, this hierarchy can be explained to a large extent by body size relationships. A second assumption of the standard cascade model is that trophic links not prohibited by the hierarchy occur with equal probability. Using nonparametric contingency table analyses, we tested this "equiprobability hypothesis" in 16 published animal food webs for which the adult body masses of the species had been estimated. We found that when the hierarchy was based on body size, the equiprobability hypothesis was rejected in favor of an alternative, "predator-dominance" hypothesis wherein the probability of a trophic link varies with the identity of the predator. Another alternative to equiprobabilty is that the probability of a trophic link depends upon the ratio of the body sizes of the two species. Using nonparametric regression and liklihood ratio tests, we show that a size-ratio based model represents a significant improvement over the cascade model. These results suggest that models with heterogeneous predation probabilities will fit food web data better than the homogeneous cascade model. They also suggest a new way to bridge the gap between static and dynamic food web models.
级联模型成功地预测了已报道的食物网中的许多模式。该模型的一个关键假设是存在一个预先确定的营养级层次结构；猎物在层次结构中的位置总是低于它们的捕食者。至少有三项研究表明，在动物食物网中，这种层次结构在很大程度上可以通过体型关系来解释。标准级联模型的第二个假设是，未被层次结构禁止的营养联系发生的概率相等。我们使用非参数列联表分析，在16个已发表的动物食物网中检验了这个“等概率假设”，这些食物网中物种的成体体重已被估算。我们发现，当层次结构基于体型时，等概率假设被拒绝，转而支持另一种“捕食者优势”假设，即营养联系的概率随捕食者的身份而变化。等概率的另一种替代假设是，营养联系的概率取决于两个物种的体型比例。我们使用非参数回归和似然比检验表明，基于体型比例的模型比级联模型有显著改进。这些结果表明，具有异质捕食概率的模型比同质级联模型能更好地拟合食物网数据。它们还提出了一种弥合静态和动态食物网模型之间差距的新方法。
