A Robust Measure of Food Web Intervality and the Dimension of Niche Space
Daniel B. Stouffer, Northwestern University, 2145 Sheridan Road, Room E136, Evanston, IL 60208 and Luis A. N. Amaral, Chemical and Biological Engineering, Northwestern University, 2145 Sheridan Rd, TECH E136, Evanston, IL 60208.
We propose a mathematically robust measure for food web intervality. Intervality of a food web---the complex network of trophic interactions between species in an ecosystem---is related to the number of trophic dimensions characterizing the possible niches found within a community. We aim to determine the minimum number of variables required to describe the factors that influence the trophic organization of the species in a community. We find that empirical food webs are not interval by the strictest sense of the definition. However, upon comparison to suitable null hypotheses, we conclude that empirical food webs exhibit a strong bias toward contiguity of prey. Though a very computationally difficult problem, we demonstrate that much ecological information can be captured within a small number of dimensions. Our conclusion that species and their diets can be so closely mapped to a single dimension represents a tremendous insight that can, for example, guide us on how best to go about developing dynamic ecosystem models.