by Karen Street
August 2000

If enough species are extinguished, will ecosystems collapse and will the extinction of most other species follow soon afterwards? The only answer anyone can give is: Possibly. By the time we find out, however, it might be too late. One planet, one experiment. E. O. Wilson

Current estimates are that we are in the midst of a mass extinction at least as great as any in the geological record. Worldwide, some 11% of mammals and birds are threatened with extinction. About 25,000 of the more than 250,000 species of plants on Earth are classified as extinct, endangered or vulnerable (1, p. 45). In the United States, according to the Nature Conservancy, 1% of native species are extinct, and about 30% are vulnerable to some degree (4, p. 67). Estimates that half of all species will die off in the next 40 to 100 years are reported repeatedly in the literature.

The Earth has undergone five extinctions since multicellular organisms evolved some 600 million years ago. The most famous and abrupt of these was the Cretaceous-Tertiary (K-T) extinction, which led to the death of dinosaurs and the majority of animal species. All previous mass extinctions occurred over millions of years; returning to previous levels of diversity required millions to tens of millions of years.

Biodiversity has many meanings. When scientists talk about biodiversity, they are referring to the number of species, genetic variability within a species , and the variety and number of populations (more or less isolated groups of a species with limited gene flow).

So what? While rain forest, wetlands, and California’s Mediterranean-like climates might be interesting to visit, do they make a difference? Plants provide food, clothing, shelter, and medicine. Plants, animals, and microorganisms clean our water, regulate the composition of the atmosphere, control the structure and fertility of the soil, and regulate pests—disease often flourishes when ecosystems lose insect predators. Plants establish roots which decrease flooding and landslides; they affect levels of rainfall and the amount of ultraviolet radiation reaching the Earth. We use microorganisms, natural and genetically modified, for bioremediation—fixing our mistakes. We breed wild and commercial plants together to maintain crop yields. The loss of biodiversity means that the ability of the Earth to provide for us will be compromised in each of these categories.

The story of the peppered moth is well-known as an example of natural selection; it was light before the industrial revolution and dark during it. It is also a story of how genetic diversity helps species survive. No new mutation occurred to help the moth adjust to changing circumstances. Rather, both light and dark moths existed before and after England industrialized, but the relative success of the different colors changed. Variety in the moth population helped it adjust to changing circumstances. Biodiversity in a ecosystem helps the whole system adjust to weather changes throughout the year and between years, and to climate changes over time.

We don’t know all of the effects of a more barren Earth, but the consequences will be long-lasting; recovery is likely to take tens of millions of years. Evolution works best when there is variety. According to Michael Soule and Bruce Wilcox, “Death is on thing; an end to birth is something else (1, p. 132).”

Today the primary cause of species loss is habitat loss: clearcutting; shifting land use to crops or pasture, houses, and roads; either destroying large ares of the habitat or breaking it up into fragments not connected by a corridor. Reducing the area occupied by an ecosystem reduces the number of species there. Perhaps two-thirds of species live in the tropics, with over half of land species in the rain forest. In tropical and Southern temperate biomes, habitat loss will be the most important driver of biodiversity loss over the next 100 years; it is also very important in many others, such as the species-rich Mediterranean biomes of South Africa and California (3).

Over the coming 100 years, a still greater cause of loss is expected to be the burning of fossil fuels, which pollutes, increases CO2 in the atmosphere, and produces global climate change. Especially critical is climate change, which will occur faster than many ecosystems, especially those dependent on trees, can migrate—a midrange estimate is that many will have to move 300 km over the next century. Global climate change will be an important contributor to destroying boreal, lake, and stream biomes. Habitat loss and climate change will work together; the lack of corridors will interfere with migration.

Fossil fuels harm biodiversity in two other ways. Pollution from burning fossil fuels, especially in the form of acid rain, kills some ecosystems and harms other; this is the primary factor in species loss in Northern temperate biomes, and important for Mediterranean and boreal biomes. The increased CO2 in the atmosphere that causes global climate change also changes the competitiveness of different plants. (3) Already, trees in the rain forest are dying faster and being replaced by more carbon-inefficient lianas (vines). In the Southern hemisphere, competition between food crops and weeds is expected to intensify, and starvation to increase.

Islands and areas that have been disrupted—by roads, crops, or previous introduction of exotics—are especially vulnerable to invasion by exotic (foreign) species. Some exotics do not do well, but many prosper in ares with less competition and fewer enemies, supplanting native species. Invasive exotics are especially a problem in islands, and Mediterranean and lake biomes (3).

Biological predictions all have large uncertainties. Biologists don’t know the actual number of species worldwide—estimates range between 5 and 100 million—or even on any single acre. Too few people are trained in systematic biology and there’s too much work; in some localities, species have a greater chance of going extinct than of being recorded. Systematics, the science of what affects what, how, and how much, is in its early stages. Still, we should not ignore these estimates on the rate of mass extinction; original best estimates of ozone layer problems were too low, and predictions about global climate change do not appear to have been low. These predictions about species loss may be uncertain, but they are the best numbers available. And the numbers indicate serious trouble ahead.

What can we do to mitigate the extinction?

As many as 30-50% of all species are confined to 25 hotspots, 2% of Earth’s land surface. These hotspots contain large numbers of endemic species (native species not found elsewhere) and are threatened with imminent habitat destruction. About 1 in 5 of these species will become extinct no matter what we do. If we wait another 10 years, 2 in 5 of these species will become extinct (2). We can set aside vulnerable areas in protected reserves. We can “use it or lose it”, cooperatively working with the local people on alternatives to harvesting or burning timber. If no way for the local people to use the rain forest is found, we will lose it (1, p. 413). Making birth control methods available to everyone who wants them is fairly cheap, and will lower population pressure from what it otherwise would be.

Setting aside protected areas won’t protect the areas against assaults to the whole biosphere from fossil fuels, pesticides, and other pollutants. We must, through governmental and intergovernmental action as well as individual action, curb the use of these pollutants.

Scientists need to learn much more about biodiversity. Policy makers need to know much more about biodiversity and other environmental issues. Study and action should be simultaneous. The world’s governments could work more cooperatively on the environment and biodiversity: the issues are too complicated for individuals to evaluate the effect of their choices (what is the effect of living in Florida? eating fish for dinner? building with wood?) However, we as individuals can reduce our use of resources: we may not be sure whether it is better to use redwood or teak, but we do know that small city apartments do less harm than large suburban houses, and that fossil fuels cause pollution, acid rain, and global climate change.

We are creating a much less pleasurable and nourishing world. We are creating a more barren and more hostile world. What will we do about it? We can begin with education; this report is one effort in that direction. Then, perhaps our Meetings could ask these questions:
• what one environmental issue can we bring to a legislator, at the federal, state, or local level?
• what one behavior do we want to change among Meeting members, and what type of support group can we form to help Friends change that behavior?

A biome is a large community of living organisms of a single major ecological region. Return to text

1. Reaka-Kudla, M, et al. (ed) Biodiversity II (Joseph Henry Press [NAS], 1997)
2. Myers, et al. Nature (February 24, 2000) “Conserving Biodiversity Hotspots” pp. 843-5, 853-8
3. Sala, et al. Science (March 10, 2000) “Global Diversity scenarios for the Year 2100” pp. 1770-4
4. Wilson, E. O. Audubon (Nov/Dec 1999) “Final Countdown” pp 64-8
5. Wilson, E. O. (ed) Biodiversity (National Academy Press, 1988)
6. Loebner, L et al. (ed) Scientists on Biodiversity (American Museum of Natural History, 1998)

Both Nature and Science are good sources of current thinking on biodiversity loss and global climate change. Nature (May 11, 2000) has 47 pages on this subject.

The Nature Conservancy

Climate Change Impacts on the United States

Our Living Resources (U.S. Department of the Interior, National Biological Service) A Report to the Nation on the Distribution, Abundance, and Health of U.S. Plants, Animals, and Ecosystems

These are the journals writing most directly on biodiversity loss:
Conservation Ecology
Conservation Biology
Restoration Ecology
Ecological Restoration
Biological Conservation
Biodiversity and Conservation
Biodiversity Letters
Journal of Applied Ecology
Ecological Applications
Applied Vegetation Science
Natural Areas Journal

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