Population deletions

We tend to focus on extinction as a species-level phenomenon, but doing so substantially understates the impact we are having. So long as a single population of a species is extant the species is not extinct, even if 99.9% of its populations have been eliminated. Species may be eliminated from most of their former range and persist only in small refuge areas. About a decade ago, population declines in amphibians began to receive world-wide attention. Hobbs and Mooney [5] cite several similar examples:⁶

• Yellow-legged frog (Rana muscosa) - 1989 survey found in only 1 of 27 sites where it had been found 10 years before.

• Owens pupfish (Cyprinodon radiosus) - Originally widespread in Owens Valley. Once thought extinct. A single population was rediscovered in 1956.

• 26 six species of west Australian mammals occur only as remnant populations occupying less than 20% of their original range. 42% of mammals originally found in the wheatbelt region are no longer found there, although only 14% of those are extinct in the entire state.

• Half of the bird species in the agricultural part western Australia have declined in distribution and abundance since 1900.