Ref ID : 1540
Hugh J. Maclsaac and John J. Gilbert; Competition between Keratella cochlearis and Daphnia ambigua: effects of temporal patterns of food availability. Freshwater Biology 25:189-198, 1991
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1. Population growth rates and relative competitive abilities of the rotifer Keratella cochlearis f. tecta and the small-bodied cladoceran Daphnia ambigua were studied under different schedules of food addition but equal total food quantity (per 4-day interval). The initial population growth rate of Keratella was significantly affected by the feeding schedule and by the presence of competitors, while that of Daphnia was affected by neither factor. Population densities of both species tended to increase as the frequency of food addition increased. 2. Daphnia suppressed and excluded Keratella from mixed-species cultures when food was provided intermittently at a high concentration, but it failed to exclude the rotifer when food was provided in a near-continuous supply at low concentration. Keratella had only a minor suppressive effect on Daphnia in all mixed-species treatments. 3. Starvation experiments indicate that Daphnia is able to withstand food shortages for significantly longer periods of time than Keratella. These and other results indicate that the outcome of interspecific competition between these species may be influenced by the frequency and concentration at which food is supplied. Daphnia ambigua is competitively superior to K. cochlearis when food is concentrated of 'pulsed', but much less so when ambient food levels are chronically low. Patterns of food availability may have important effects in determining the relative abundance of rotifers and small cladocerans in natural zooplankton communities.