Comentarios de profesor de Harvard - 129829

A continuación se encuentran ejemplos de especies extintas y en peligro y algunos comentarios sobre las causas de la pérdida de biodiversidad.

The Baiji is a graceful, freshwater dolphin that once abounded along a thousand miles of the Yangtze River. It may now be the world's most endangered large animal. Caught in a vise of rising pollution and indiscriminate fishing during the past century, its population fell to only 400 by 1980, to 150 in 1993, and is now below 100. Zoologists doubt the species will survive in the wild for another decade. The baiji's closest rivals for early extinction include the Sumatran rhinoceros (probably fewer than 500 individuals survive) and the giant panda of China (fewer than 1,000).

The media can be counted on to take note when the last member of each of these species dies, or, like the California condor, is removed from the wild to be placed in a captive breeding program. But for every animal celebrity that vanishes, biologists can point to thousands of species of plants and smaller animals either recently extinct or on the brink. The rarest bird in the world is Spix's macaw, down to one or possibly two individuals in the palm and river-edge forests of central Brazil. The rarest plant is Cooke's koki'o of Hawaii, a small tree with profuse orange-red flowers that once graced the dry volcanic slopes of Molokai. Today it exists only as a few half plants--branches implanted onto the stocks of other related species. Cooke's koki'o may spend its last days in this biological limbo; despite the best efforts of horticulturists to assist the plant, no branches planted in soil have sprouted roots.

Around the world, biodiversity, defined as the full variety of life from genes to species to ecosystems, is in trouble. Responding to the problem, conservation experts have in the past two decades shifted their focus from individual species to entire threatened habitats, whose destruction would cause the extinction of many species. Such "hot spots" in the U.S., for example, include the coastal sage of Southern California, the sandy uplands of Florida, and the dammed and polluted river systems of Alabama and other Southern states. Arguably the countries with the most hot spots in the world are Ecuador, Madagascar and the Philippines. Each has lost two-thirds or more of its biologically rich rain forest, and the remainder is under widespread assault. The logic of the experts is simple: by concentrating conservation efforts on such areas, the largest amount of biodiversity can be saved at the lowest economic cost. And if the effort is part of the political process during regional planning, the rescue of biodiversity can gain the widest possible public support.

In hot spots around the globe, mass extinctions of local populations have been commonplace. Among them:

More than half the 266 species of exclusively freshwater fishes in peninsular Malaysia.

Fifteen of the 18 unique fishes of Lake Lanao in the Philippines, and half the 14 birds of the Philippine Island of Cebu.

All of the 11 native tree-snail species of Moorea in the Society Islands. Those on nearby Tahiti, as well as in the Hawaiian Islands, are rapidly disappearing.

More than 90 plant species growing on a single mountain ridge in Ecuador, through clear-cutting of forest between 1978 and 1986.

These well-documented cases notwithstanding, it is notoriously difficult to estimate the overall rate of extinction. Some groups, like the larger birds and mammals, are more susceptible to extinction than most. The same is true of fishes limited to one or two freshwater streams. Most kinds of insects and small organisms are so difficult to monitor as to make exact numbers unattainable. Nevertheless, biologists using several indirect methods of analysis generally agree that on the land at least and on a worldwide basis, species are vanishing 100 times faster than before the arrival of Homo sapiens.

- Only Humans Can Halt the Worst Wave of Extinction Since the Dinosaurs Died by E.O. Wilson

- http://raysweb.net/specialplaces/pages/wilson.html