Until our own generation, no one had grounds to worry whether the next generation would survive or enjoy a planet worth living on. Ours is the first generation to be confronted with these questions about its children’s future. We devote so much of our lives to training our children to support themselves and to get along with other people. Increasingly, we’re asking ourselves whether all these efforts of ours might be wasted.
The threat to the extinction of life on the planet can be categorized under two heads. First being nuclear holocaust first revealed in Hiroshima. Everyone agrees that the threat is real.
The other threat is the risk of an environmental holocaust, of which one often discussed potential cause is the gradual extinction of most of the world’s species. In contrast to the nuclear threat, there is almost complete disagreement about the risk of mass extinction is real and whether it would do us real harm if it occurred.
Every species depends on other species for food and for providing its habitat. Thus species are connected to each other like branching rows of dominoes. Just as toppling one domino will topple some others, so too the extermination of one species may lead to the loss of others, which may, in turn push still others over the brink. This mechanism of extinction may be described as a ripple effect. Nature consists of so many species, connected to each other in such complex ways, that it is virtually impossible to foresee where the ripple effect from the extinction of any particular species may lead.
For example, fifty years ago, no one anticipated that extinction of big predators - Jaguars, Pumas, and harpy eagles on Panama’s Barro Colorado island would lead to the extinction there of little antbirds, and to massive changes in the tree-species composition of the island’s forest. But it did, because the big predators used to eat medium-sized predators like peccaries, monkeys and coatimundis, and medium-sized seedeaters like agoutiis and pacas. With the disappearance of big predators, there was population explosion of the medium-sized predators, which proceeded to eat up the antbirds and their eggs. The medium-sized seedeaters also exploded in abundance and ate large seeds that had fallen on the ground, thereby suppressing the propagation of tree species producing large seeds and favoring instead the spread of competing tree species with small seeds, and hence to an explosion of mice and rats feeding on small seeds, and hence to an explosion in hawks, owls, and ocelots preying on those small rodents. Thus, the extermination of three uncommon species of big predators will have triggered a rippling series of changes in the whole plant and animal community, including the extinction of many other species.
We find people who dismiss the significance of decrease in biodiversity. So long as human beings are not among them. They need to understand that like other species we too depend on other species for our existence in many ways. Some of the most obvious ways are that other species produce the oxygen that we breathe, absorb the carbon dioxide that we exhale, decompose our sewage, provide our food, maintain the fertility of our soil and provide our wood and paper.
Then could not we preserve just those particular species and let other species go extinct? Of course not, because the species that we need also depend on other species. Just as Panama’s antbirds coiuld not have anticipated their need for Jaguars, the ecologogical rows of domipnoes is too complex for us to have figured out which dominoes we can dispense with. For instance, could anyone please answer these three questions:
Which ten tree species produce most of the world’s paper pulp: For each of these ten tree species, which are the ten bird species that eat most of its insect pests, the ten insect species that pollinate most of its flowers, and the ten animal species that spread most of its seeds? Which other species these insects and animals depend on? You’d have to be able to answer these three impossible questions, if you are the president of a timber company trying to figure out which species you can afford to let go extinct.