World is losing 1,000 species a year Disappearance: It used to be that the natural rate of extinction was one to three species a year. Now humanity finds itself in the midst of a mass extinction, with only mankind itself to blame.

Sun Journal

January 14, 1998

The following article is taken from the Worldwatch Institute's "State of the World, 1998," released last weekend.

The biodiversity around us today is the result of more than 3 billion years of evolution. Species declines and extinctions have always been a natural part of that process, but there is something disturbingly different about the current extinction patterns.

Examinations of the fossil record of marine invertebrates suggest that the natural or "background" rate of extinctions -- the rate that has prevailed over millions of years of evolutionary time -- claims something on the order of one to three species per year. In stark contrast, most estimates of the current situation are that at least 1,000 species are lost a year.

Like the dinosaurs 65 million years ago, humanity now finds itself in the midst of a mass extinction: a global evolutionary convulsion with few parallels in the entire history of life. But unlike the dinosaurs, we are not simply the contemporaries of a mass extinction -- we are the reason for it.

Out of almost 4,400 mammal species, about 11 percent are "endangered" or "critically endangered." Another 14 percent remain vulnerable to extinction and an additional 14 percent come very close to qualifying as threatened.

These "near-threatened" species tend to have larger population sizes or to be relatively widespread, but nonetheless face pressures that have them on the fast track to threatened status in the not-too-distant future.

One near-threatened species is the African red colobus monkey. Its huge range stretches from Senegal to Kenya, but the red colobus faces hunting pressure and habitat loss everywhere it occurs, and is declining in numbers.

The biggest culprit in the loss of mammalian diversity is the same as that for birds -- habitat loss and degradation.

As humankind converts forests, grasslands, rivers, wetlands and deserts for intensive agriculture, tree plantations, industrial development and transportation networks, we relegate many mammals to precarious existences in fragmented, remnant habitat patches that are but ecological shadows of their former selves.

The major reason primates are so threatened is their affinity for tropical forests, a habitat under siege around the globe. In regions where forest degradation and conversion have been most intense, such as South and East Asia, Madagascar and the Atlantic forest of eastern Brazil, on average 70 percent of the endemic primate species face extinction.

In addition to habitat loss, at least one in five threatened mammal species faces direct over-exploitation -- excessive hunting for meat, hides, tusks and medicinal products, and persecution as predators of and competitors with fish and livestock.

Mammals in most regions have been less susceptible than birds to invasive species, but there is one big exception -- the unique marsupial and rodent fauna of Australia, long isolated from other continents.

The introduction of non-native rabbits, foxes, cats, rats and other animals has combined with changing land-use patterns during the past two centuries to give Australia the world's worst modern record of mammalian extinction.

Nineteen mammal species have gone extinct since European settlement in the 18th century, and at least a quarter of the remaining native mammalian fauna remains threatened.

The causes of fish endangerment -- habitat alteration, introduction of non-native species and direct exploitation -- are no different from those affecting other species, but they appear to be more pervasive in aquatic ecosystems.

Freshwater aquatic habitats receive a heavy blow from humanity. More than 40,000 large dams and hundreds of thousands of smaller barriers plug up the world's rivers -- altering water temperatures, sediment loads, seasonal flow patterns and other river characteristics to which native fish are adapted. Levees disconnect rivers from their flood plains, eliminating backwaters and wetlands that are important fish spawning grounds.

River engineering affects distant lakes and estuaries, whose ecologies decline when river inflows are altered.

Agricultural and industrial pollution of waterways further reduces habitat for fish and other aquatic life. Agricultural runoff in the Mississippi River basin is now so extensive that when the river enters the Gulf of Mexico, the over-fertilized brew of nutrients it carries sparks huge algal blooms, which deplete the water of oxygen and create a "dead zone" of about 6,800 square miles -- nearly the size of New Jersey.

Introductions of non-native, often predatory fish can unravel diverse native fish populations in just a few years, precipitating a cascade of local extinctions.

About 34 percent of threatened fresh-water fish face pressure from introduced species, but none have been more devastated than the sunfish-like cichlids of East Africa's Lake Victoria, the world's second-largest freshwater lake.

Baltimore Sun Articles
Please note the green-lined linked article text has been applied commercially without any involvement from our newsroom editors, reporters or any other editorial staff.