One of Earth's rarest fish, the Devil's Hole pupfish, is often cited as an unusual example of a small but long-lasting population of animals. But these fish may not have been isolated for as long as once thought.
Less than 100 adult pupfish (Cyprinodon diabolis, pictured) live in a small pool in the southwestern United States, and they have supposedly been there for 10,000 to 20,000 years. Michael Reed at Tufts University in Medford, Massachusetts, and Craig Stockwell at North Dakota State University in Fargo analysed genetic data from C. diabolis, along with their numbers over time. They concluded that the fish have been living in this pool for only a few hundred to a few thousand years, and will probably become extinct within the next 400 to 3,000 years.
This means that C. diabolis is no exception to the rule that small, isolated populations cannot persist for long.