is negative frequency-dependent
selection by predators, particularly in regard to prey that are different morphs of a polymorphic species
that is not a mimic
(non-mimetic) of another species. The idea links up with the concept of "search image" from Luuk Tinbergen
, whereby - through experience - a predator is considered to have developed a particular skill or capacity to spot prey items of typical appearance (mainly pattern), to the point where typical specimens are even taken disproportionately to their actual abundance within the population. Conversely, specimens of unusual appearance are less likely to end up as part of a predator's diet than would be "justified" if consumption of food items was related to their abundance within the population in a straightforward way. In consequence, there are greater-than-"expected" chances of individuals within a population that are of non-typical appearance passing on the genes
controlling that appearance to the next generation.