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Population bottlenecks increase genetic drift, as the rate of drift is inversely proportional to the population size, which is reduced. It also changes the relationship of natural selection (see: inbreeding).
| Year | Estimated bison population size |
| Before 1492Events January 2 Boabdil, the last Moorish King of Granada, surrenders his city to the army of Ferdinand and Isabella after a lengthy siege. March 30 Ferdinand and Isabella sign a decree aimed at expelling all Jews from Spain unless they convert to Roman | 60,000,000 |
| 1890Events January 2 Alice Sanger becomes the first female staffer for the U. White House. January 25 The United Mine Workers of America is founded. January 25 Nellie Bly completes her round-the-world journey in 72 days. March 1 Leon Bourgeois succeeds Ernest | 750 |
| 2000This page is about the year 2000. See 2000 AD for the UK comic book, Number 2000 for other uses. 2000 is a leap year starting on Saturday (see link for calendar), and also the International Year for a Culture of Peace''. Events Y2K passes without the seri | 350,000 |
The population of American bison fell due to overhunting, nearly leading to extinction around the year 1890 and has since begun to recover.
A classic example of a population bottleneck is that of the northern elephant seals, whose population fell to about 30 in the 1890's although it now numbers in the tens of thousands.
All existing cheetahs are extremely close genetically suggesting an extreme population bottleneck in the past.
Another largely bottlenecked species is the Golden hamster, for which the vast majority are descended from a single litter found in the Syrian desert around 1930.
Sometimes further deductions can be inferred from an observed population bottleneck. Among the Galapagos archipelago's giant tortoises (themselves a prime example of a founder effect), the comparatively large population on the slopes of Alcedo volcano is significantly less diverse than four other tortoise populations on the same island. Researchers' DNA analysis dates the bottleneck around 88,000 ybp, according to a notice in Science, October 3, 2003. About 100,000 ybp the volcano erupted violently, burying much of the tortoise habitat deep in pumice and ash. The coincidence is suggestive.