Chemically-mediated communication structures food webs. Several chemically mediated
effectsonthe target organismshave been observed (Cembella, 2003;
Vos et al., 2006), such as kairomones of fish affecting Daphnia
migration. Chemical signals are easily transported in water (Wolfe,
2000), but can also be degraded by microbial activity (von Elert and
Loose, 1996; Hagstro¨m et al., 2007).