Food availability and initial relative abundance determine the outcome of interspecific competition between two different‐sized cladocerans

Abstract

Competition amongst different‐sized cladocerans has attracted the interest of many researchers because of their similar life strategies and overlap in feeding habits. To test the combined effects of food concentration and initial relative abundance on the competition outcomes between small‐ and large‐bodied cladocerans, we grew large Daphnia magna and small Moina micrura with two initial relative abundances under five algal densities. At the lowest food concentration (0.10 mg L−1 carbon), D. magna could not maintain a population in the presence or absence of M. micrura. Under conditions in which both species grew together, food levels as high as 0.30 mg L−1 favoured superior population growth of D. magna, irrespective of inoculation abundance. Under conditions in which both species had equal initial abundance, population growth of M. micrura was inhibited by the presence of Daphnia at ≥0.30 mg L−1 food levels. M. micrura was superior to D. magna at higher food concentrations (≥0.60 mg L−1) and high initial abundance. These results suggest that population growth of large Daphnia was more successful than that of small Moina when the food availability was low, while the small Moina dominated under conditions of high initial abundance and high food supply. Therefore, interspecific competition amongst cladocerans depends not only on the size of competing species, but also on their initial relative abundance and food availability.