Here's a breakdown:

* Species: A group of organisms that can interbreed and produce fertile offspring.

* Subspecies: Distinct populations within a species that have unique characteristics and are geographically isolated from other populations. They can still interbreed with other subspecies of the same species.

Here are some examples:

* Eastern Gray Squirrel (Sciurus carolinensis) has several subspecies, such as the Florida Gray Squirrel (Sciurus carolinensis carolinensis) and the Northern Gray Squirrel (Sciurus carolinensis leucotis).

* Black-Footed Ferret (Mustela nigripes) is a species with only one subspecies recognized.

It's important to remember that subspecies are a taxonomic concept, and their recognition can sometimes be debated by scientists.