WHAT DO WE MEAN BY EXTINCTION?

by Whit Gibbons

February 4, 2007

"Extinct" is a word that will continue to exist, as it has for five centuries. According to the Oxford English Dictionary, the word was first used in 1432. Like many commonly used words, "extinct" can be depicted in different ways, including five fairly discrete categories

Dinosaurs and millions of other prehistoric species can be placed in the category of prehuman extinction, the end-line of natural evolutionary processes, a condition no human can be blamed for. The next category is that of human-caused extinctions, such as the passenger pigeon and dodo bird, although no one alive today can be held accountable.

A species that existed in our lifetime but is no longer present falls into a third category--modern extinction. Humans living today can be held responsible, at least in part, for most modern extinctions. The causes leading to or hastening modern extinctions include such obvious ones as killing individuals for sport or commercial harvest. Direct killing and conspicuous forms of pollution get attention and generate an emotional public reaction, and global climate change will soon be indicted for some modern extinctions. But the foremost culprit and continuing threat in regard to modern extinctions is the destruction of natural habitats.

The fourth category is a term I first saw used in the Wall Street Journal--commercially extinct, which is of course appropriate terminology for a business-oriented newspaper. A commercially extinct species is no longer economically feasible to harvest, although the species may be present, even abundant, in some areas. The Atlantic codfish, once a staple food item in Boston, is now considered by some experts to be commercially extinct.

The fifth category is ecologically extinct. Unfortunately, this is too often the stage at which we begin to pay attention. Once a species becomes ecologically extinct, keeping it extant (in existence) requires biological life-support systems. For example, the California condor was once ecologically extinct, but U.S. Fish and Wildlife Service programs demonstrated that recovery is possible. This magnificent species survived for awhile on a human-designed welfare system, with the young being raised in captivity. Some now roam free, but their fate is still as precarious as ours would be if were clinging to a cliff edge in the Grand Canyon.

A fundamental measure of a species' condition is whether it is extinct or extant. Black or white. But ecological gray zones of impending extinction should attract our notice. Is the species declining in its abundance or geographic distribution? The spotted turtle serves as an example of the problem.

At least a couple of human generations will go by before the spotted turtle, one of the prettiest turtles in North America, will be declared a modern extinction. However, this little black turtle with bright yellow spots on the shell unquestionably has declined in numbers throughout its range. Two reasons are apparent, both related to the ecology of the species.

First, spotted turtles are popular pets, and people who like pet turtles will pay a lot of money for one. Thus, turtle collectors capture them for the pet trade. The problem: spotted turtles seldom occur in large numbers in any one place. Those living in small wetland habitats are often present in low numbers. The removal of a few dozen adults may effectively eliminate the population, leading to commercial extinction of the spotted turtle.

The other assault on spotted turtles comes from habitat destruction. These animals, like many other wildlife species, depend on wetland habitats. The loss of small, marshy wetlands means a decrease in the amount of suitable wildlife habitat. Who can argue that we have fewer spotted turtles now than we did even two decades ago? We definitely have fewer wetlands. Before long the spotted turtle will be ecologically extinct.

We should be concerned about spotted turtles now, before they become commercially, then ecologically, extinct. Let's deal with how habitat loss and overharvesting affect their ecology today, so we do not have to institute welfare and life-support systems tomorrow. The spotted turtle is only one example of a threatened species. Hundreds of other examples would serve as well. We aren't going to eliminate the word "extinct" from the world's vocabulary. But we might limit the number of species to which the term must be applied.

If you have an environmental question or comment, email