Alarm substances
Alarm substances from crushed conspecifics act as enhancers of change (Pijanowska 1997; Pijanowska and Kowalczewsk 1997; Stabell et al. 2003; Laforsch et al. 2006); however, there are also reports indicating almost no change caused by alarm substances (Stirling 1995; Walls and Ketola 1989; Parejko and Dodson 1990). Given intraspecific variation, both results are possible. Alarm cues may not be sufficient to identify species predators, and the set of defensive traits subsequently expressed may be misleading, but it does provide reliable evidence of being captured during the predation cycle. Unless it is a specific defense, adaptation suggests that the higher the cue concentration the higher the expression of an inducible defense. This alarm cue is thought to spread across a narrow range, resulting in variations in plasticity between individuals according to their receipt of the cue. Without widespread diffusion of alarm cues, individuals would not experience the same concentration of cues, and hence there would be differences in how they react.