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.