  Apparent competition between species is believed to be one of the principle
driving forces that structure ecological communities, although the precise
mecha nisms have yet to be characterized. Here we develop a model system that
isolates phage-mediated interactions by neutralizing resource competition using
two genetically identical Bordetella bronchiseptica strains that differ only in
that one is the carrier of a phage and the other is susceptible to the phage.
We observe and quantify the competitive advantage of the bacterial strain
bearing the prophage in both invading and in resisting invasion by bacteria
susceptible to the phage, and use our measurements to develop a mathematical
model of phage-mediated competition. The model predicts, and experimental
evidence confirms, that the competitive advantage conferred by the phage
depends only on the relative phage pathology and is independent of other phage
and host parameters. This work combines experimental and mathematical
approaches to the study of phage-driven competition, and provides an
experimentally tested framework for evaluation of the effects of
pathogens/parasites on interspecific competition.
