Lake victoria in africa had hundreds of species of cichlids, all diverged from a single ancestor less than 10,000 years ago. There were many species that all utilized the same food source but in diffrent parts of the lake. There were at least 5 species that ate exclusively zooplankton. One of the species was always found in the top 6 feet of water. Other species migrated through the day following the food. Other species lived deep or inshore or over rocky bottms, exclusively.
Because of abundant resources, constant food supplies, sexual selection, and variable habitat many species are able to co-exsist on the same food supply. Even though they eat the same food they don't eat the same prey at the same time in the same place. (If your a geek like me you would enjoy the book "Darwin's Dream Pond", its about the evolution of cichlids)
Black crappie and white crappie may eat exactly the same thing but they do so in diffrent places. Black crappie live inshore and white crappie live offshore. They may live on the same food sources, or on what ever happens swims infront of them. Over time they make small adaptions, spawn at slightly diffrent times and live in diffrent places. In a large lake they may not compete at all, in a pond there is little difference between inshore and offshore and they probably wouldn't coexsist well.
It is possible that niether one represents the "original" but that instead the ancestor is a planktivore generalist, that adapted to a slightly larger size and the ability to eat minnows. And then that split in half, one for inshore on for off.
