Size and variation in individual growth rates among food web modules

AbstractThe complexity of food webs can be reduced to fundamental modules of trophic interactions that repeat to form reticulate webs. Omnivory, defined as feeding on more than one trophic level, is a module that is found in food webs more often than predicted by chance, likely because it confers stability. Yet, little is known about how omnivore and other food web modules affect individuals in the food web. Here, we constructed four different experimental food web modules using a blue mussel predator, zooplankton consumer, and phytoplankton resource. By manipulating the predator's access to the consumer and providing resource subsidies, we produced exploitative competition, food chain and omnivory food web modules, and a consumer‐resource interaction. We used RNA:DNA ratios to measure the growth rate of the consumer in each food web. In 24‐h experiments, growth rates of the consumer in the omnivory food web were significantly higher and more variable than in the other modules. Our results suggest that higher growth rates and variation at the individual scale may weaken the strength of predator–consumer interactions and help explain the ubiquity of omnivory in real food webs.