Pop

A population of warblers lives in a forest Which of these events would cause an evolutionary change in the wall

does not involve natural selection?

cous trait to the warbler population

A "bottleneck event" might decimate part of a population by coincidence. Consider a pop of lizards, brown and green. A natural disaster might wipe out, by chance, the brown lizards. So the evolutionary change would come from the survival and reproduction of the green lizards that remain.