Food quality and food threshold: implications of food stoichiometry to competitive ability of herbivore plankton

Abstract

Exploitative competition for food resources is considered to be an important factor determining the dominant species in communities. In such a competition, a threshold food concentration (TFC), where the growth rate becomes zero, is crucial in determination of competitive outcomes. In addition, recent studies on ecological stoichiometry have suggested that the TFC of a species would differ due to changes in food elements that limit growth. If the magnitude of change in TFC differs between species, competitive superiority among species may also change. The experiments showed that the rank order of the species in TFC changed according to the P content of food, suggesting that competitively superior species can vary with elemental composition of food. These results imply that as well as quantity, the elemental composition of food is important in exploitative competition, and the changes in elemental composition of food may be critical to shape an entire community structure.