Examine the following scenario: a population of small fish lives in a lake (lake a). the dark-colored fish are the ancestral phenotype and represent the usual coloration of the species. the bright-colored fish, however, arose over time. there is a steady rise in the population of bright-colored fish. both populations thrive. suppose that a short land barrier separates lake a from another small lake with a population of only the normal dark-colored fish (lake b). after torrential rains lasting for days, the lakes overflow and a few of the bright-colored fish from lake a are washed into lake b. list the sequence of evolutionary mechanisms which have come into effect in each event.