Over-exploitation

Many of the best-documented cases of individual species being driven to extinction or near-extinction by humans are those of over exploitation.

The passenger pigeon, was in the early 1800s the most abundant bird in North America, and so plentiful that migrating flocks of a billion or more individuals were seen. By the end of the last century it had been hunted to the brink of extinction, and in September of 1914, the passenger pigeon disappeared forever with the death of the last remaining bird (Martha) in a zoo in Cincinnati.

The American bison, or buffalo, (figure 7), of the Great Plains was also nearly hunted out of existence in the same century, and its larger, woods-dwelling relative was driven to extinction.

The current and rapid loss of tropical hardwoods in many regions is due to high commercial demand, low rates of successful replacement, and the long periods of growth necessary to produce new, marketable resources.

During the last two decades, the world has seen the collapse of a number of marine fisheries. Even for those populations that appear to recover, the consequences of the original over-exploitation are only poorly understood. It has been observed that there is generally a decrease in the size, and hence age, of the individuals harvested. The selective loss of larger fish has significant impacts on those that remain. If fertility is strongly related to body size, as is the case for many fish species, over-exploitation will not only reduce the abundance but may also make recovery more difficult by removing the most fertile individuals.