3. Categorized factors associated with variations in inducible defense
We identified seven secondary factors causing variations in inducible defense based on previous studies (Fig. 1); abiotic factors, ecological and evolutionary traps, food, alarm substance, clone/genotypes, instars, and maternal effect. The following three factors were not noted owing to the paucity of prior research or controversy: abiotic factor, ecological trap, and alarm cue (Fig. 1).
The seven factors can be distinguished by their relative relationship to primary factors (Fig. 2). One is the primary factors to promote or inhibit the degree of expression in inducible defense by working with the primary factors; abiotic factors, food, clone/genotype, and instars. The other is the secondary factor alone can express predator-induced plasticity, but the degree of expression may be equivalent, smaller or larger compared with the induction traits from the primary factor; abiotic factors, ecological evolutional traps, alarm substance, and maternal effect. If organisms can express an inducible defense with as few factors as possible, it would be adaptive to take less cost than to perceive a number of factors. To the cost of factor acquisition (DeWitt et al. 1998), organisms would try to assess environment to express phenotype-environment matching. Given the avoidance of mismatching phenotypes, secondary factor may help the control, accelerate, and limit of the expression of defensive plasticity, in addition to ensuring the reliability of primary factors.