The Biodiversity Crisis
Scientists estimate that species extinctions are currently 500–1000 times the normal, or background, rate seen previously in Earth’s history. The current high rates will cause a precipitous decline in the planet’s biodiversity in the next century or two. The loss of biodiversity will include many species we know today. Although it is sometimes difficult to predict which species will become extinct, many are listed as endangered (at great risk of extinction). However, many extinctions will affect species that have not yet been discovered. Most of these “invisible” species that will become extinct currently live in tropical rainforests like the Amazon basin. These rainforests are the most diverse ecosystems on the planet and are being destroyed rapidly by deforestation. Between 1970 and 2011, almost 20 percent of the Amazon rainforest was lost.
Biodiversity is a broad term for biological variety, and it can be measured at a number of organizational levels. Traditionally, ecologists have measured biodiversity by considering the number of species and the number of individuals of each species (known as relative abundance). However, scientists are using different measures of biodiversity, including genetic diversity, to help focus efforts to preserve the biologically and technologically important elements of biodiversity.
Biodiversity loss refers to the reduction of biodiversity due to displacement or extinction of species. The loss of a particular individual species may seem unimportant to some, especially if it is not a charismatic species like the Bengal tiger or the bottlenose dolphin. However, the current accelerated extinction rate means the loss of tens of thousands of species within our lifetimes. Much of this loss occurs in tropical rainforests like the one pictured in Figure 1, which are very high in biodiversity but are cleared for timber and agriculture. This is likely to affect human welfare through the collapse of ecosystems dramatically.
Environmental scientists recognize that human populations are embedded in ecosystems and depend on them, just as is every other species on the planet. Agriculture began after early hunter-gatherer societies settled in one place and heavily modified their immediate environment. This cultural transition has made it difficult for humans to recognize their dependence on living things other than crops and domesticated animals. Today our technology smooths out the harshness of existence and allows many of us to live longer, more comfortable lives. Still, ultimately the human species cannot exist without its surrounding ecosystems. Our ecosystems provide food, medicine, clean air and water, recreation, and spiritual and aesthetical inspiration.
Types of Biodiversity
A common meaning of biodiversity is simply the number of species in a location or on Earth; for example, the American Ornithologists’ Union lists 2078 species of birds in North and Central America. This is one measure of the