title: Model ecosystems with random nonlinear interspecies interactions.
abstract: The principle of competitive exclusion in ecology establishes that two species living together cannot occupy the same ecological niche. Here we present a model ecosystem in which the species are described by a series of phenotypic characters and the strength of the competition between two species is given by a nondecreasing (modulating) function of the number of common characters. Using analytical tools of statistical mechanics we find that the ecosystem diversity, defined as the fraction of species that coexist at equilibrium, decreases as the complexity (i.e., number of characters) of the species increases, regardless of the modulating function. By considering both selective and random elimination of the links in the community web, we show that ecosystems composed of simple species are more robust than those composed of complex species. In addition, we show that the puzzling result that there exists either rich or poor ecosystems for a linear modulating function is not typical of communities in which the interspecies interactions are determined by a complementarity rule.
authors.affiliation: Instituto de Física de São Carlos, Universidade de São Paulo, Caixa Postal 369, 13560-970 São Carlos, São Paulo, Brazil.
authors.forename: Danielle O C
authors.initials: DO
authors.lastname: Santos
authors.forename: José F
authors.initials: JF
authors.lastname: Fontanari
mesh_terms: D000818:Animals; D005075:Biological Evolution; D003163:Competitive Behavior / Q000502:physiology*; D003198:Computer Simulation; D017753:Ecosystem; D014644:Genetic Variation; D005828:Genetics, Population; D006801:Humans; D008954:Models, Biological; D017711:Nonlinear Dynamics; D011157:Population Dynamics; D012641:Selection, Genetic; D013045:Species Specificity; D016019:Survival Analysis