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Abstract:
The hypothesis was tested that zooplankton can adapt to fluctuations of their food resources at intermediate time scales in order to maximize their energy input. The cladoceran Daphnia pulicaria and the rotifer Brachionus rubens were cultured at a range of fixed growth rates and then offered radioactively labelled algae at limiting and non-limiting concentrations to determine their functional response. Rotifers and cladocerans showed a remarkably similar response. Animals growing at low growth rates had higher maximum filtering rates. i.e. were better adapted to low food concentrations than those growing at high rates. The growth rate did not affect the maximum ingestion rate in any of the species, thus indicating that adaptation to the prevailing food conditions was based on the process of food collection. Both species were heavier when cultured at high growth rates. Plotting the weight-specific maximum filtering rate versus the growth rate resulted in a pronounced negative slope. The slope for the weight-specific maximum ingestion rate was also negative. Hence filtering and ingestion rates seem to be determined by the size of the zooplankton, not by their weight.
