Influence of temperature on life-history characteristics of two sibling species of Eurycercus (Cladocera, Chydoridae)

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Abstract
Life history characteristics of 2 sibling species of chydorid Cladocera, E. (Bullatifrons) longirostris and E. (B.) vernalis, were determined under controlled laboratory conditions. Temperature-dependent change in embryonic development time was described by the Belehradek rate-temperature function. Intra- and inter-specific variation was considerable and underlines the need for population-specific determinations of egg development time over a wide temperature range (especially low temperatures) if secondary production is to be assessed reliably. The relationships between egg development time and generation time with temperature in geographically separated populations of both species exhibited compensation. The interaction between age-specific fecundity and temperature is discussed in relation to population dynamics. Values of r declined with temperature and, although comparable to those calculated for littoral Cladocera, are lower than most estimates available for limnetic species. The life history traits employed by these 2 large-bodied species with variable brood size are contrasted with those of the small species of chydorids with maximum brood size of 2 eggs.
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