The origin of polymorphic crypsis in a heterogeneous environment.

Polymorphic crypsis has been observed in several taxa, but has, until now, lacked a firm theoretical understanding. How does a single morph, well camouflaged in one type of habitat, evolve crypsis in another, not isolated, habitat? We here analyze a model of one prey species living in two different habitats connected by passive dispersal. We find that the rate of dispersal, the trade-off between crypticity in the habitats, and the amount of predation determines whether the prey species can become cryptic in two different habitats through evolutionary branching. Intermediate values of all parameters seem to promote evolutionary branching leading to polymorphism, and a more extreme value of one parameter can be balanced by another. Other parameter combinations lead to either a single habitat specialist or an intermediate generalist type, partly cryptic in both habitats. When the predator follows a type III functional response, the parameter space for when the prey will undergo evolutionary branching is remarkably larger than the corresponding parameter space for a type II functional response. Evolutionary branching can occur both at the intermediate generalist strategy, or close to a specialist strategy.