The Sixth Extinction

The Sixth Extinction Chapter 9 Summary & Analysis

Summary
Analysis
In Brazil, near the Venezuelan border, there is a square-shaped area known as Reserve 1202. Reserve 1202 consists of 25 acres of untouched rainforest, and all around it there is “scrub” (the remains of rainforest areas where the trees were cut down). There are many other similar Reserves in the area, all controlled by the Biological Dynamics of Forest Fragments Project (BDFFP), an organization founded in the 1970s by Tom Lovejoy. Lovejoy wanted a way to protect certain rainforest areas from farmers and ranchers cutting down trees. He presented a plan to the Brazilian government, and ever since then he has been given grants to study the rainforest preserves. Lovejoy’s research involves making comparisons between the tiny reserves and the main rainforest area, miles away.
In the previous chapter, we discussed the direct relationship between land area and biodiversity. The purpose of Tom Lovejoy’s organization is to isolate small patches of rainforest and measure the biodiversity there, in order to give science a better idea of what will happen in the future, when the entire rainforest has been reduced to a few 25-acre patches.
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Of the approximately fifty million square miles of land on the surface of the Earth that contain no significant ice, humans have developed more than 25 million. Indeed, the development of ice-less land is one of the defining characteristics of the Anthropocene era. However, it can be difficult to decide what does and doesn’t count as development—for example, is a tropical rainforest with a pipeline running through it developed or not? To the extent that there is undeveloped land anymore, it probably looks like Reserve 1202—an “island” in the middle of a “sea” of development.
One of the major challenges facing scientists who study global warming is to define what does and doesn’t constitute undeveloped land. Furthermore, scientists have to face the possibility that developed land can still harbor considerable biodiversity; for example, a rainforest that has been partly destroyed to clear way for a pipe would continue to harbor great biodiversity. These complex questions exemplify the unprecedented difficulties of climate science.
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Kolbert goes to Reserve 1202 with an ornithologist named Mario Cohn-Haft. Cohn-Haft takes Kolbert out into the forest late at night to listen to birdcalls. An expert at identifying birdsong, he explains that, over the course of his many years at Reserve 1202, he’s noticed a gradual decline in the diversity of bird species, and in biodiversity overall.
Cohn-Haft’s observations support a possibility that Kolbert suggested in the previous chapter: the decline in available land area will cause a marked decline in observed biodiversity, both for birds and in general.
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Islands tend to have relatively few species when compared with the mainland. Perhaps the reason for this is that there isn’t enough space for many different species to develop or even survive. Over time, islands experience a phenomenon called “relaxation”—a gradual reduction in biodiversity. This is due to the fact that, with a limited number of species and a small amount of space, temporary setbacks to diversity are more likely to be devastating. On a large continent, the destruction of a few bird eggs would have almost no impact on the species’ success in the long run; on a small island, however, the destruction of these eggs could spell the end of the species.
In this passage, Kolbert explains why there is a direct relationship between land area and biodiversity. The smaller the land area, the greater the likelihood that an accident (such as the breaking of a few eggs) could prove catastrophic for an entire species. Theoretically, one might think that a small patch of rainforest could harbor the same amount of biodiversity as an entire rainforest—and at first, it would. But eventually, small accidents would reduce the total biodiversity in the patch.
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Cohn-Haft drives Kolbert away from Reserve 1202 and into the main rainforest, where he conducts tests and collects samples to compare with those from Reserve 1202. He shows Kolbert dozens of different plants and animals, explaining that the rainforest is an extremely diverse ecosystem and focusing his comments on one species in particular—the army ant, Eciton burchellii. Army ants are unlike any other ant species on the planet—they’re very aggressive and they travel constantly. There are more than 300 species that derive some kind of nutrition from army ants.
The army ant is an excellent example of a species on which other species depend. If all the army ants in a rainforest were to disappear, than hundreds of other species would lack for food. This further explains the direct relationship between biodiversity and land area—in a small area, where one species might be in greater danger of extinction, that species’ extinction would set off a chain reaction that results in the extinction of other animals and plants, too.
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Since the seventies, there has been a lot of research into the number of insect species in the rainforests. One entomologist (insect scientist) named Terry Erwin estimated that rainforests contained at least 30 million species of arthropod (a group representing insects, spiders, and centipedes). Other scientists have argued that Erwin was overestimating the biodiversity of rainforests, but, regardless, it’s clear that rainforests are home to a staggering number of different life forms. One result of this biodiversity is that human deforestation efforts are particularly destructive to rainforest life. Some have estimated that even a one percent loss in the area of untouched rainforest results in a quarter of a percent loss of all the species in the rainforest. This means that some five thousand rainforest species go extinct every year.
Even if scientists like Erwin have overestimated the decline in biodiversity, it’s clear that the decline of available land area poses a significant threat to the biodiversity of the world’s rainforests. This is another example of the magnitude of the effects of human activity on the natural world. As we’ve seen, a small decline in the land available for rainforest creatures could set off a chain reaction resulting in the extinction of many interconnected plants and animals.
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Throughout the nineties and 2000s, a series of science articles argued that a rainforest species went extinct every day, if not every minute. Later studies have shown that these estimates of the extinction rate were exaggerated. It is possible that the effects of reducing the amount of available land take time to set in. It is also possible that deforested areas can regrow over time—meaning that human development isn’t necessarily permanently reducing the amount of available land on the planet. Another possibility is that humans aren’t very good at counting the number of vanished species.
Kolbert introduces a couple of caveats to her observations so far. These caveats are important, as the science of biodiversity has yet to explain the observed conditions of the changing rainforests. The fact that Kolbert admits it when scientific research hasn’t explained something satisfactorily lends weight to her conviction that, despite the lingering questions,, the bulk of the evidence suggests that deforestation will reduce biodiversity.
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Lovejoy is still involved with BDFFP today, though he’s in his seventies. His main priority is building support for the BDFFP, and for environmentalism in general, using evidence gathered from the BDFFP to educate the public. Lovejoy argues that many species have vanished from his reserves in the last few decades, suggesting that the fragmentation of the rainforest ecosystem results in rapidly shrinking biodiversity.
Lovejoy’s personal anecdotes about the decline in biodiversity in the rainforests reinforce the findings of the scientists Kolbert has discussed elsewhere in this chapter. Deforestation is a devastating blow to biodiversity, even (or especially) in the most biodiverse places on earth.
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One night at Reserve 1202, Kolbert wakes up to watch an “army ant parade.” She’d been told that she’d see a huge group of ants marching through the forest, but no ants appeared. Cohn-Haft, who had woken up to watch as well, explains that the army ants were probably preparing to go into “statuary phase”—one of the few times when they remained in one place for an extended period—and thus wouldn’t appear that night after all. Kolbert hears the sounds of birds, which had been expecting the ants to march, as well. She realizes that the night is a metaphor for the rainforest itself: for every one species that disappears, hundreds of other species are affected.
The chapter ends on another poignant note: the disappearance of the army ants from the rainforest symbolizes the gradual disappearance of biodiversity from the planet. If army ants do go extinct, then many other animals, such as birds, will have to find new food sources or go extinct, too. In short, the extinction of even one insignificant-seeming species could start a catastrophic chain-reaction, the result of which is mass-extinction.
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