The effects of predation on phenotypic and life history variation in an aquatic vertebrate

Predation has the capacity to influence prey directly through modulating the density and size structure of the population (Bronmark et al., 1995) and/or indirectly by altering the population by causing changes in growth, survival and fecundity rates (Fraser and Gilliam, 1992). As a result, prey species have evolved a number of defense mechanisms to minimize their risk of being detected, caught and consumed by predators (Sih, 1987; Lima and Dill, 1990; Chivers and Smith, 1998; Kats and Dill, 1998). These defenses include adaptations in behaviour, morphology and life history traits (Chivers and Smith, 1998; Chivers and Mirza, 2001). Several studies have shown that prey have the ability to alter their phenotypes in response to predation threat (Bronmark and Miner, 1992; Trussel, 1996; Reimer and Tedengre, 1996; Weber and Declerck, 1997; Van-Buskirk and Schmidt, 2000; Kappes and Sinsch, 2002). Such phenotypic plasticity has important ecological consequences as the changes result in the modification of species interactions. For example, when exposed to caged predators (Aeschna, dragonfly larvae) two species of larval newts {Triturus alpestris and T. helveticus) developed darker tail fin pigmentation, larger heads, larger tails and spent more time hiding in the leaf litter in comparison with newts in predator-free ponds. The individuals with the predator-induced phenotype survived significantly longer during survival trials when exposed to free dragonfiy larvae (VanBuskirk and Schmidt, 2000). In another study, Bronmark and Miner (1992) found that crucian carp {Carassius carassius) in the presence of piscivorous pike {Esox lucius) developed deeper bodies than those not exposed to this gape limited predator. The increase in size resulted in a refuge from predation.