Extinction Has Five Faces - via Herp Digest

by Whit Gibbons, Savannah River Ecology Lab, University of Georgia October 14, 2018

"Extinct" is a word first used in 1432 according to the Oxford English Dictionary. 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 pre-human extinction, the end-line of natural evolutionary processes, a condition no human can be blamed for. The second category is human-caused extinctions, such as passenger pigeons, Carolina parakeets and dodos, for which 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, some much more than others, for most modern extinctions. The causes leading to modern extinctions include such obvious ones as direct killing and unregulated pollution. But the foremost culprit and continuing threat to most wildlife is human destruction of natural habitats.

The fourth category is a term I first saw used in the Wall Street Journal – commercially extinct, which is 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. Commercial extinction can be a precursor to complete elimination. The Atlantic codfish, once a staple food item in Boston, is now considered by some experts to be almost commercially extinct.

The fifth category is ecologically extinct. Unfortunately, these fourth and fifth categories are often the stages at which we begin to pay attention. Once a species becomes ecologically extinct, keeping it extant (in existence) requires biological life support. 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 persisted for a while 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 we were clinging to a cliff ledge in the Grand Canyon where a few survive.

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 abundance or geographic distribution? The spotted turtle is 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 in the wild, mostly illegally, for the pet trade. The problem: spotted turtles, even when they occur in large numbers in a wetland, can be easily collected and removed. The removal of egg-laying females can effectively eliminate a population.

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 suitable wildlife habitat. We definitely have fewer wetlands, so who can argue that we have fewer spotted turtles now than we did even two decades ago? The spotted turtle is on a trajectory toward ecological extinction.

We should be concerned about all wildlife now, before they become commercially or ecologically extinct. Let's deal with how habitat loss and over harvesting affect their life cycles and 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. The word "extinct" will continue to exist, but we can limit the number of species to which the term must be applied.