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Abstract

Eudiaptomus gracilis and Eudiaptomus graciloides are amongst the most common calanoid copepods in Europe and co-occur in many lakes. To understand their ecological dynamics, it is essential to know their responses to environmental variation. The finding that E. graciloides exhibits diapause in winter, whereas E. gracilis reproduces throughout the year indicates that the two species might differ in their temperature responses. We measured embryonic and naupliar development times, clutch size (number of eggs per sac), hatching percentage and body length of the first copepodid stage (CI) of both species under non-limiting food conditions at different temperatures. Special attention was given to individual variability on development times and to the use of the gamma density function (GDF) for fitting the probability of moulting. Results show that E. gracilis exhibits just slightly faster development times, lower individual variability, higher hatching percentage and larger clutches than E. graciloides and that extreme temperatures affected E. gracilis less intensely than E. graciloides. GDF was a good tool for estimating individual variability in the different experiments.