Food
Food level is not only a basic element of growth, but also a critical factor in modifying inducible defenses [e.g., depth-selective behavior (Loose and Dawidowicz 1994); morphological defenses (Tollrian 1995); life history traits (Jeyasingh and Weider 2005; Stibor and Navarra 2000; Weetman and Atkinson 2002). For instance, inducible defense under low food level is expressed, but to a lesser extent (Barry 1995; Hanazato 1991). The degree of expressed plasticity has been found to be greater at high food levels and lower at low food levels, with other clones responding in the opposite direction (Jeyasingh and Weider 2005). In predation experiments on the same size Daphnia raised under different food conditions, Daphnia clones under low food conditions were more likely to be preyed by Chaoborus larvae easy (Jeyasingh and Weider 2005). However, it is worth nothing that Daphnia clones in the high food condition had a more variable susceptibility to be eaten. The rich food conditions may give Daphnia a variety of ways to adaptation.