Most ecological theories deal with simple consumer--resource interactions. Scientists at Ecole Normale Supérieure (Paris) and McGill University provide a novel approach to incorporate nontrophic interactions, such as pollination and habitat modification, in ecosystem models, which allows them to study the dynamics of complex interaction webs.
Their model adds nontrophic interactions to a food web in the form of modifications of trophic interactions. It also tracks nutrient fluxes in the food web and hence satisfies the principle of mass conservation.
Using this model, they show that nontrophic interactions can profoundly influence ecosystem properties such as species diversity, biomass, and production. In turn, the nature, prevalence, and strength of species interactions depend on species diversity. Counterintuitively, strong positive interactions tend to deteriorate ecosystem functioning because consumers become very efficient at exploiting their resources.
"Nontrophic interactions are still poorly studied theoretically, and their impact on biodiversity and ecosystem functioning was largely unknown," says Michel Loreau, Canada Research Chair in theoretical ecology.
"We hope that our new approach will boost their study and contribute to a more comprehensive theory of complex ecological systems. Organisms interact in many other ways than through feeding on each other or competing for shared resources," he adds. "Ecology should be able to account, not only for the diversity of species, but also for the diversity of their interactions."
The study, "Nontrophic interactions, biodiversity, and ecosystem functioning: an interaction web model," by Alexandra Goudard (Ecole Normale Supérieure and Université Pierre et Marie Curie) and Michel Loreau (McGill University) was published in the January issue of the American Naturalist.
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