Food is one of the most important factors limiting natural populations of plankton (Weglenska 1971, Lampert 1978). The prospect of a food shortage determines the outcome of interspecific interclonal competition, while freshwater animals can plastically respond to fluctuations in food availability by adjusting their phenotype to the current and future (predicted) food levels, changing for example their filtering apparatus (Lampert Brendelberger 1996). Daphnia living under conditions of food scarcity can also "prepare" their offspring for a predicted further decline, making them more resistant to starvation (Gliwicz Guisande 1991). Because a decrease in the availability of food is often caused by an increase in the density of plankton-ic grazers, both crowding and the low level of food itself can theoretically inform Daphnia about the possibility of starvation in the future, especially when other limiting factors are not present in the environment. Many studies have viewed crowding as a negative factor capable of inhibiting Daphnia growth and reproduction (e.g. Guisande 1993, Matveev 1993, Burns 1995). In contrast, its role as a signal informing Daphnia of a future deficiency of food has gone unexplored. The main goal of this study was to check whether crowding and food deficiency could bring about the release of neonates of Daphnia better prepared for starvation, and whether this resistance to starvation of neonates is correlated with their size.
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