Trait and density mediated indirect interactions in simple food webs

This article compares indirect trait-mediated interactions in simple resource–consumer–predator food webs with those that are density-mediated. It focuses on two well documented responses of consumers to predation risk: decrease in consumer activity and habitat switch. These behavioral effects are transmitted to resources and they cause similar indirect effects as those which are mediated by density changes in consumers. Two indirect interactions are studied in this article: trophic cascades, and apparent competition. Results for density only, trait only and combined density and trait mediated interactions are compared and discussed with respect to manipulation with predator density (top-down manipulation) and resource environmental capacity (bottom-up manipulation). The article shows that trait-mediated effects on species equilibrial densities are similar to those of density-mediated, but they are often highly non-linear. Thus, they may have potential for even stronger impact on food webs than those which are density mediated.