The probabilistic niche model reveals the niche structure and role of body size in a complex food web

Abstract

The niche model has been widely used to model the structure of complex food webs, and yet the ecological meaning of thesingle niche dimension has not been explored. In the niche model, each species has three traits, niche position, diet positionand feeding range. Here, a new probabilistic niche model, which allows the maximum likelihood set of trait values to beestimated for each species, is applied to the food web of the Benguela fishery. We also developed the allometric nichemodel, in which body size is used as the niche dimension. About 80% of the links in the empirical data are predicted by theprobabilistic niche model, a significant improvement over recent models. As in the niche model, species are uniformlydistributed on the niche axis. Feeding ranges are exponentially distributed, but diet positions are not uniformly distributedbelow the predator. Species traits are strongly correlated with body size, but the allometric niche model performssignificantly worse than the probabilistic niche model. The best-fit parameter set provides a significantly better model of thestructure of the Benguela food web than was previously available. The methodology allows the identification of a numberof taxa that stand out as outliers either in the model's poor performance at predicting their predators or prey or in theirparameter values. While important, body size alone does not explain the structure of the one-dimensional niche. © 2010 Williams et al.