Defining and measuring the impact of dynamic traits on interspecific interactions.
Trait- and density-mediated indirect effects describe different pathways by which indirect interactions in food webs are propagated from one species to another, through changes in intermediate species. A series of articles in Ecology has progressively altered the original definitions of "trait-mediated" to the point where understanding is being impeded. The most recent of these articles are two meta-analyses that use "trait-mediated" to describe the demographic costs to a prey species of employing anti-predator defenses. These same articles introduce a companion term, "density-mediated interaction", apparently to describe direct and indirect interactions that only involve changes in population density due to consumption by predators. This new terminology has many disadvantages, including (1) using a general term for a relatively narrow group of processes; (2) using "mediated" in a manner inconsistent with existing terminology; (3) confusing the accepted definitions of different types of indirect effects; and (4) providing a highly incomplete measure of the impact of behavior on the predator-prey interaction. Solutions to these problems and the meaning of the meta-analyses are discussed.
Abrams
Peter A
PA
Department of Ecology and Evolutionary Biology, Zoology Building, University of Toronto, 25 Harbord Street, Toronto, Ontario M5S3G5, Canada. abrams@zoo.utoronto.ca
D000818:Animals; D017753:Ecosystem; D020387:Food Chain; D008954:Models, Biological; D008962:Models, Theoretical; D011156:Population Density; D011157:Population Dynamics; D011235:Predatory Behavior / Q000502:physiology*; D013045:Species Specificity