PARENT SESSION
Oral Session #58: Theoretical Ecology.
Presiding: M. Neubert
Wednesday, August 7. 8:00 AM to 11:30 AM. Grand Ballroom East, Radisson.
Trait initiated direct and indirect effects in food webs.
Abrams, Peter*,1, 1 Department of Zoology, Toronto, Ontario, Canada
ABSTRACT- Most theory in community ecology has addressed the consequences of species addition or removal, but much of community change is likely to be driven by changes in the characteristics of species that are already present. Previous work has mainly considered the role of dynamic traits as transmitters of indirect interactions. It is important to develop a body of theory predicting the possible changes in the densities of other species that are produced by environmentally-driven change in the characteristics of one or more focal species. Models of simple food webs containing 2 to 6 species are analyzed to determine how a change in the a demographically important characteristic in one species will change its own density and the densities of other species in the food web. These characteristics are per capita resource capture rates, per capita death rates, and efficiencies of converting food into offspring. Most of the analysis focuses on models with three trophic levels. Many counter-intuitive responses to changes in traits occur. In the case of two independent prey sharing a common predator, increases in the vulnerability of one prey to the predator may increase or decrease the population density of its apparent competitor. In the case of two competing prey sharing a common predator, increases in the vulnerability of one prey species to its predator may increase its own population density. The magnitude of 'trait-initiated' effects of one species on a second can be very sensitive to the traits of species that are relatively distant in the food web structure. Several examples of this phenomenon are illustrated using models of 5 or 6 species on 3 trophic levels.
KEY WORDS: trait initiated effect, indirect effect, community response, food web