TABLE 6–1 Estimates of Potential Species Extinction in the Tropics

Estimate

Basis of Estimate

Source

1 species/day to 1 species/hour between 1970s and 2000

Unknown

Myers, 1979

33–50% of all species between the 1970s and 2000

A concave relationship between percent of forest area loss and percent of species loss (see Table 6–2)

Lovejoy, 1980

A million species or more by end of this century

If present land-use trends continue

National Research Council, 1980

As high as 20% of all species

Unknown

Lovejoy, 1981

50% of species by the year 2000 or by the beginning of next century

Different assumptions and an exponential function (see Table 6–2)

Ehrlich and Ehrlich, 1981

Several hundred thousand species in just a few decades

Unknown

Myers, 1982

25–30% of all species, or from 500,000 to several million by end of this century

Unknown

Myers, 1983

500,000–600,000 species by the end of this century

Unknown

Oldfield, 1984

0.75 million species by the end of this century

All tropical forests will disappear and half their species will become extinct

Raven, Missouri Botanical Gardens, personal communication to WRI and IIED, 1986

33% or more of all species in the 21st century

Present rates of forest loss will continue

Simberloff, 1983

20–25% of existing species by the next quarter of century

Present trends will continue

Norton, 1986

15% of all plant species and 2% of all plant families by the end of this century

Forest regression will proceed as predicted until 2000 and then stop completely

Simberloff, 1986

world was losing one species per day in the 1970s, and by the mid-1980s, the loss will increase to about one species per hour. By the end of this century, our planet could lose anywhere from 20 to 50% of its species (Table 6–1). Humans are the basic cause of these losses, because in the process of securing a living from the land, people modify it. The human population is growing at a faster rate in tropical latitudes than anywhere else, and this results in more habitat destruction in the tropics. In fact, the greatest losses of species are reported to occur in the tropics, which contain half of the world’s remaining forests. Some writers suggest that present tropical forests will be destroyed by the beginning of the next century and that because these forests are the world’s richest in terms of species numbers, their destruction becomes the primary source of a global loss of species.

How are these scenarios derived? What are the bases of these calculations? How firm are they? To develop such scenarios, three types of data are needed: the



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