title: The inverse niche model for food webs with parasites.
abstract: Although parasites represent an important component of ecosystems, few field and theoretical studies have addressed the structure of parasites in food webs. We evaluate the structure of parasitic links in an extensive salt marsh food web, with a new model distinguishing parasitic links from non-parasitic links among free-living species. The proposed model is an extension of the niche model for food web structure, motivated by the potential role of size (and related metabolic rates) in structuring food webs. The proposed extension captures several properties observed in the data, including patterns of clustering and nestedness, better than does a random model. By relaxing specific assumptions, we demonstrate that two essential elements of the proposed model are the similarity of a parasite's hosts and the increasing degree of parasite specialization, along a one-dimensional niche axis. Thus, inverting one of the basic rules of the original model, the one determining consumers' generality appears critical. Our results support the role of size as one of the organizing principles underlying niche space and food web topology. They also strengthen the evidence for the non-random structure of parasitic links in food webs and open the door to addressing questions concerning the consequences and origins of this structure.
authors.affiliation: 2019 Kraus Natural Science Building, Department of Ecology and Evolutionary Biology, University of Michigan, 830 North University Avenue, Ann Arbor, MI 48109-1048 USA ; Department of Neurology, Mayo Clinic, 200 First St. SW, Rochester, MN 5590 USA.
authors.forename: Christopher P
authors.initials: CP
authors.lastname: Warren
authors.affiliation: 2019 Kraus Natural Science Building, Department of Ecology and Evolutionary Biology, University of Michigan, 830 North University Avenue, Ann Arbor, MI 48109-1048 USA ; Howard Hughes Medical Institute, Chevy Chase, MD USA.
authors.forename: Mercedes
authors.initials: M
authors.lastname: Pascual
authors.affiliation: Western Ecological Research Center, US Geological Survey. c/o Marine Science Institute, University of California, Santa Barbara, CA 93106 USA.
authors.forename: Kevin D
authors.initials: KD
authors.lastname: Lafferty
authors.affiliation: Department of Ecology, Evolution and Marine Biology, Marine Science Institute, University of California, Santa Barbara, CA 93106 USA.
authors.forename: Armand M
authors.initials: AM
authors.lastname: Kuris
keywords: Food web structure; Food webs with parasites; Niche model