species, the species complement in western Ecuador must have amounted to 200,000 or more in all. Since 1960, at least 95% of the forest cover has been destroyed to make way for banana plantations, oil exploiters, and human settlements of various sorts. According to the theory of island biogeography, which is supported by abundant and diversified evidence, we can realistically expect that when a habitat has lost 90% of its extent, it will eventually lose half its species. Precisely how many species have actually been eliminated, or are on the point of extinction, in western Ecuador is impossible to say. But ultimate accuracy is surely irrelevant, insofar as the number must total tens of thousands at least, conceivably 50,000—all eliminated or at least doomed in the space of just 25 years.

Very similar baseline figures for species totals and endemism levels, and a similar story of forest depletion (albeit for different reasons and over a longer time period), apply to the Atlantic-coastal forest of Brazil, where the original 1 million square kilometers of forest cover have been reduced to less than 50,000 square kilometers (Mori et al., 1981). Parallel data apply also to Madagascar, where only 5% of the island’s primary vegetation remains undisturbed—and where the endemism levels are rather higher (Rauh, 1979).

So in these three tropical forest areas alone, with their roughly 600,000 species, the recent past must have witnessed a sizeable fallout of species. Some may not have disappeared as yet, due to the time lag in equilibration, i.e., delayed fallout effects stemming from habitat depletion. But whereas the ultimate total of extinctions in these areas in the wake of deforestation to date will presumably amount to some 150,000 species, we may realistically assume that already half, some 75,000 species, have been eliminated or doomed.

Deforestation in Brazil’s Atlantic-coastal forest and Madagascar has been going on for several centuries, but the main damage has occurred during this century, especially since 1950, i.e., since the spread of broad-scale industrialization and plantation agriculture in Brazil and since the onset of rapid population growth in Madagascar. This all means that as many as 50,000 species have been eliminated or doomed in these areas alone during the last 35 years. This works out to a crude average of almost 1,500 species per year—a figure consistent with the independent assessment of Wilson (1987), who postulates an extinction rate in all tropical forests of perhaps 10,000 species per year. Of course many reservations attend these calculations. More species than postulated may remain until a new equilibrium is established and causes their disappearance. Conversely, more species will presumably have disappeared during the later stages of the 35-year period than during the opening stage. Whatever the details of the outcome, we can judiciously use the figures and conclusions to form a working appraisal of the extent that an extinction spasm is already under way.


The outlook for the future seems all the more adverse, though its detailed dimensions are even less clear than those of the present. Let us look again at tropical forests. We have seen what is happening to three critical areas. We can identify a good number of other sectors of the biome that feature exceptional

The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement