Print PageLife history omnivory or size-induced mixed competition/predation systems have theoretically been shown to be fragile at the same time as existing empirical data suggests such systems to be common in nature. In a whole lake experiment covering 17 years, we analyzed the effects of the introduction of the intraguild prey roach (Rutilus rutilus) on the population size and individual performance of the intraguild predator perch (Perca fluviatilis) and resource levels in two low productive systems.
Results/Conclusions
A strong long-term effect of roach on the zooplankton resource but not on the macroinvertebrate resource was present. Competitive effects of roach on perch were observed in one of the lakes the first years after the introduction, but at the end of the study no competitive effect of roach on any size class of perch was observed in any of the two lakes. In contrast, a positive predatory effect reflected in improved growth rates of perch was present. An overview of other studies that have argued that mixed competition/predation interactions were important in the study systems suggests that the dynamics of these systems may be explained without invoking mixed interactions. Overall we argue that the importance of mixed competition/predation interactions may have been overrated.
