If a population becomes isolated from other populations of the same species and then genetic differences start to occur, what happens?

What do we call a group of individuals that can reproduce successfully in nature?

A population is best described as....

The flowers of pink tulips open in the morning, while the flowers of lavender tulips open in the early afternoon. The bees that pollinate these tulips cannot carry pollen back & forth between the two types of tulips because of their flowers being closed at different times of day. What type of isolation is this?

The emergence of new rivers or streams is a type of ____________ isolation.