Over 20% of species of mammals are threatened in many parts of the world
Threatened Mammals Jan 1997 Scientific American
For some time, many naturalists have felt that the world is entering a period of major species extinction, rivaling five other periods in the past half a billion years. A new study by the World Conservation Union (also known as the IUCN), issued in October 1996, provides strong support for this theory. Using more thorough study methods than previously, the IUCN finds a niuch higher level of threat to several classes of animals than was generally thought. It found that an astonishing 25 percent of mammal species-and comparable proportions of reptile, amphibian and fish species-are threatened. Of five classes of animals, birds are the least at risk [see barchart]. Of the 4,327 known mammal species, 1,096 are at risk, and 169 are in the highest category of "critically endangered'extremely high risk of extinction in the wild in the immediate future. (The other two are "endangered," meaning very high risk in the near future, and 'vulnerable," a high risk in the medium-term future.) Of the 26 orders of mammals, 24 are threatened. Among the most affected are elephants, primates and Perissodactyla species (such as rhinoceroses and tapirs).
Although the IUCN data probably understate the number of threatened mammal species in some regions, it is possible to draw conclusions about the pattern on the map, in particular, that habitat disturbance by humans increases the threat to mammals. Also important is a high proportion of endemic species, especially in the case of geographically isolated areas. Such regions havo unique evolutionary histories and fixed boundaries to species ranges, and thus, degradation of such habitats is more likely to take a toll on animals. Striking examples are the Philippines and Madagascar, where 32 and 44 percent, respectively, of all mammal species are threatened. In both countries, well over half the species are endemic, and habitat disturbance is high. In contrast are Canada and the U.S. with, respectively, 4 and 8 percent of mammal species threatened. Less than a quarter of the species in the U.S. and only 4 percent in Canada are endemic. Habitat disturbance is moderately above average in the U.S. and very low in Canada. The countries with the most threatened mammals are Indonesia, with 128 species, and China and India, both with 75. These three account for 43 percent of the world's population and are among the most densely populated. -RodgerDoyle
Threatened Birds Scientific American Sept 97
New Zealand Birds, a Case
There are many reasons for protecting birds, not the least of which is the delight we take in watching them. It's sad, then, to note that 1,107 bird species-11 percent of the globe's total-are at risk of dying out. This report comes from a major new study by IUCN (also known as the World Conservation Union) and BirdLife International, the world's chief organization concerned with threatened birds. Their data show that 168 bird species are "critically endangered'-meaning they face an extremely high risk of extinction in the wild in the immediate future. (The other two IUCN risk categories are "endangered,' or very high risk of extinction in the near future, and 'vulnerable,' or high risk in the medium-tec,m future.) Birds, like other animal groups, are most threatened in island habitats, and indeed, of the 104 bird species that became extinct in the past 400 years, about 90 percent lived on islands. Island species, particularly in the tropics, are often found nowhere else on the planet and therefore cannot be replenished from outside. Such species have few defenses against such introduced predators as cats and dogs, and their habitats may be constricted by non-indigenous herbivores such as goats. Furthermore, they are vulnerable to introduced diseases. lt is no wonder, then, that the two countries with the highest risk for birds are the Philippines and New Zealand. In both places, 15 percent of species are threatened. But of all islands with sizable populations, Hawaii, at 33 percent, has the highest proportion of threatened bird species. Significant threats to bird life exist in continental areas as well, such as South America, because of exploitation of the tropical forest. Although the proportion of avian species threatened is moderately low, this region supports a huge variety of birds, and so the absolute number of species at risk is quite large, as shown by the numbers on the map. The comparatively high rates in China and India probably result in part from population pressure. The risk on other continents is low, but that does not necessarily indicate an absence of major problems.
New Scientist Paradise Postponed 17 Jan 98
In Europe, for example, where only 1 to 2 percent of species are threatened, a quarter of all species classified as not threatened have suffered significant declines in the past 20 years. In the continental U.S., where the threat to birds is also low, several once widespread species have vanished altogether, including the passenger pigeon and the colorful Carolina parakeet. Among several bird orders, more than 20 percent of species are threatened. They include pheasants, quails, parrots and macaws, all of which are threatened by habitat loss and exploitation by hunters and traders. Also of concern are albatross and petrels, which breed on small oceanic islands. Many species of rails, cranes and kagus are also at high risk because they are very slow-breeding animals, making them extremely vulnerable to disturbance of nesting grounds and wintering areas. Songbirds, which account for almost 60 percent of all bird species, have a slightly below-average risk of extinction, but some species, including those in American grasslands, are in serious decline. -Rodger Doyle ([email protected])
Plants at Risk in the US Scientific American Aug 97
Loss of plant species, even those that are rare, may lead to ecological imbalance. Furthermore, rare plants may prove of economic or medicinal value, as in the case of the meadowfoam wildflower, which contains high-grade industrial oil. It is therefore of some concern that almost a third of all plant species in the U.S. appear to be at risk, a substantially larger proportion than in the case of mammals and birds. The record of plant species extinction is incomplete but suggests that the current rate is considerably higher than historical norms. (Over the past 200 years, at least 13 plant species have gone extinct, and an additional 125 have not been seen for years and may also be lost forever.) This assessment con)es from the Nature Conservancy of Arlington, Va., and its partners in the Natural Heritage Network, organizations that have measured the risk of extinction to individual species by considering rarity, population trends and known threats. The map is based on their data for about 16,000 species of higher plants native to the U.S. Higher plants-also called vascular plants-generally have stems, leaves and roots. They include conifers, ferns and flowering plants and span such diverse species as Douglas fir, sugar maple, sagebrush, saguaro cactus, California poppy and Kentucky bluegrass. (Nonvascular plants, which include such groups as mosses and liverworts, account for a small fraction of all plant species.) Habitat loss or degradation is the single biggest threat to native plant species, but other, less obvious factors come into play. Introduced plants and animals, for example, have been invading natural habitat;, posing serious threats to native flora. (Introduced plant species, which number about 5,000, are not included in the map or chart.) Factors peculiar to particular states or regions also have a decisive role. In Hawaii, for example, most of the nearly 1,200 native species are endemic-found nowhere else on the earth. Extreme endemism, combined with a large number of nonindigenous plants and major habitat alteration by both Polynesians and Europeans, has made Hawaii's flora the most threatened of any state. Plant species in the upper Great Plains and much of the Midwest are the least threatened, partly because of the fairly uniform climate, topography and geology, conditions that favor species with widespread ranges. Additionally, during the period of Pleistocene glaciation, rare species tended to become extinct, whereas widespread species were more likely to survive south of the glacier and repopulate the land as the ice receded. California harbors more native plant species than any other state and has the second highest proportion of species at risk. The state's large size and diverse habitats provide abundant opportunities to adapt and evolve, giving rise to numerous narrowly restricted species, which are vulnerable to California's spectacular urban and agricultural growth. Certain other areas, such as Oregon, the southern Rocky Mountain states, Florida and Georgia, also have high proportions of rare species because of the great diversity of their habitats. Areas of patchwork mountain and desert, which provide ample opportunities for geographical isolation, are especially rich in locally evolved plant species. Extreme examples of such habitats are the mountaintop 'sky islands' in the deserts of New Mexico and Arizona, many of which support local and rare plant species. -Rodger Doyle ([email protected])