CONTENTS
- The Earth and Its People
- Pollution and Health Risks
- Feeding a Future World
- Freshwater: Lifeblood of the Planet
- Oceans in Decline
- Forests: The Earth's Lungs
- Endangered Biodiversity
- Toward a Livable Future
HIGHLIGHTS
- Can development be sustained?
- Scientists point to environmental distress syndrome
- Cities grow ever larger
- Global temperatures rising
- Are we setting the stage for our own extinction?
- World population must stabilize
Population Reports is published by the Population Information Program, Center for Communication Programs, The Johns Hopkins School of Public Health, 111 Market Place, Suite 310, Baltimore, Maryland 21202-4012, USA
Fall 2000
Series M, Number 15
Special Topics
No one knows the true scope of biodiversity—how many species of plants and animals share the planet with human beings. Most estimates put the number at somewhere between 10 million and 30 million, with some consensus around the figure of 14 million (43, 56, 143, 163). In any case, only about 1.7 million species—a small share of the total—have been identified and categorized, while even fewer have been studied (162, 163).
Whatever the actual number of species, preservation of biodiversity itself is vital to humanity. Currently, over 40,000 species of plants, animals, fungi, and microbes are regularly exploited for human benefit (56). An estimated 40% of modern drugs come from the wild, worth some US$40 billion a year in over-the-counter and prescription sales (217).
Biodiversity is essential to agriculture. After 10,000 years of settled agriculture and the discovery of some 50,000 varieties of edible plants, just 15 food crops provide 90% of the world's food energy intake. Three of them—rice, wheat and corn (maize)—are the staple foods of 4 billion people (73, 75, 257).
Dependence on only a few crops can be dangerous because disease can spread rapidly through monocultures—as it did through the Irish potato harvest, starving one-fifth of the country's population in the 1840s (181). Cultivars (cultivated plants) need to be cross-bred every 5 to 15 years to give them greater resistance to diseases and insects, as well as to introduce new yield-enhancing traits, such as increased tolerance for drought or saline soils.
Without repeated infusions of new genes from the wild, geneticists cannot continue to improve staple crops. Since 1900 about three-quarters of the genetic diversity of cultivars has been lost, as well as nearly half of the wild gene pool of domestic animals (73, 217).
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 Heraldo Castro/Conservation International |
| Endangered species. Left: Sumatra rhino. Right: Madagascar lemur. Humans share the planet with at least 10 million other animal and plant species. Biological diversity is crucial to the world's ecology, and probably to the future of humanity itself. Yet human actions and numbers are sending thousand of species into extinction—most in areas where human population density is highest. | |
Human Exploitation
Humankind's current patterns of resource exploitation do not bode well for the future of biodiversity. Ecologist Norman Myers recently estimated that some 600,000 species have vanished since 1950 (164). Today, two of every three species are estimated to be in decline (216).
People today use almost half the energy needed to keep all of the earth's species going. That is, human beings use about 40% of the total net primary production of the earth's green plants, which are the fundamental food source for animals. This percentage could double within a quarter century (136). Over-exploitation of plants is worrisome, as plants provide the link to all other forms of life, through photosynthesis. "All flesh is grass," biologist David Given has observed (86).
The IUCN has reported that about 5,200 species of animals currently are threatened with extinction (115), including:
- Close to 1,100 species of mammals, one-quarter of the total number of such species;
- Over 1,100 birds, 11% of the 9,600 known species of birds;
- Over 2,000 species of freshwater fish, 20% of the total number identified;
- 253 species of reptiles, 20% of the total number surveyed;
- An estimated 124 species of amphibians, 25% of the total number surveyed (216).
Nearly 40% of all freshwater fish species in the US are at risk of extinction, as are 33% of Australia's freshwater fauna, and 42% of Europe's (18). Of the 514 species of birds in Europe, 270--about two-thirds--are threatened with extinction. Of these, 200 species are migratory (100). Many migratory species are threatened because of habitat destruction at both ends of their north-south migration routes (56, 115). Two-thirds of Asia's wildlife habitats have been destroyed, many over the past five decades (233).
Plant species are not faring well, either. Of the 270,000 known species of higher plants (such vascular species as trees and flowering plants), 34,000 are endangered (116). In the US nearly 30% of the 16,000 known plant species are at risk of extinction (17). In the tropics ecosystem destruction is so severe that some 60,000 plant species, roughly one-quarter of the world's remaining total, could be lost within 25 years (112, 217, 266).
