Final answer:
A distinct breeding population separate from others is known as an isolated population or distinct population unit, often resulting from habitat isolation which can eventually lead to divergent evolution due to various evolutionary forces.
Step-by-step explanation:
A breeding population that is distinct and separate from other breeding populations of the same or similar species is sometimes called an isolated population or a distinct population unit. This occurs when individuals of a species become geographically separated, preventing them from interbreeding with other populations. Over time, natural selection, mutation, and genetic drift can result in the divergence of the two populations.
This separation can occur due to habitat isolation, where a group becomes reproductively and genetically independent from the parent species due to geographic barriers or changes. For instance, after natural events like a flood, a cricket population might be split, leading each subgroup to no longer interact with one another and, over time, possibly diverge into different populations or even species due to natural selection, mutation, and genetic drift.