Effect of prey richness on a consumer's intrinsic growth rate.

The intrinsic growth rate of non-selective microbivores increases asymptotically with increasing prey biomass, but we do not know how intrinsic growth rate is affected by prey richness. The objective of this experiment was to determine the effect of prey richness on the growth kinetics of nematode predators while grazing on mixed bacterial lawns. We found that the intrinsic growth rate of Caenorhabditis elegans in laboratory culture increased asymptotically with prey richness. The mechanism of this pattern was primarily due to the best available prey species in the mixture: the intrinsic growth rate of the consumer feeding on a mixture of prey was approximately equal to the intrinsic growth rate of the predator when feeding on the single best prey in monoculture. This was analogous to the selection effect observed in biodiversity-ecosystem functioning relationships. Generation time, and not reproductive output, was the life history trait component that was most consistent with the pattern of intrinsic growth rate. Our results suggest that in order to link invertebrate consumers' growth rates to their microbial species composition in the field, it will be necessary to determine the ability of microbivorous invertebrates to selectively forage in natural environments and to better understand the micro-scale distribution of microbial communities in their natural environments.