The Number of Species on Earth

In the species approach to conservation, biologists focus on saving individual species from extinction by studying and assessing endangered species populations and their habitats. The ecosystem approach includes studies of larger systems so that sufficient areas may be preserved to sustain healthy habitats in general.

The species approach to halting biodiversity loss depends on estimates of the number of species on Earth. The exact number will probably never be known, but the estimates used today in ecology come from counting the known species, then deriving the total number of unknown species.

The Convention on Biological Diversity has reported that 1.75 million species have been identified so far, and most scientists surmise that the actual number of all species—known and unknown—is at least 14 million. Rather than understanding the number of species on Earth, it may be more important for students of biodiversity to recognize certain hallmarks of biodiversity, as follows:

1. Species diversity increases nearer the equator.
2. Tropical rain forests cover about 7 percent of the globe’s land but hold more than 50 percent of species.
3. The loss of all species has accelerated since the year 1800.

Edward O. Wilson, curator at the Museum of Comparative Zoology at Harvard University, is one of society’s preeminent biodiversity scholars. In his classic 1988 text, Biodiversity, Wilson wrote, “No precise estimate can be made of the numbers of species being extinguished in the rain forests or in other major habitats, for the simple reason that we do not know the numbers of species originally present . . . extinction rates are usually estimated indirectly from principles of biogeography . . . the number of species of a particular group of organisms in island systems increases approximately as the fourth root of the land area. This has been found to hold true not just on real islands but also on habitat islands, such as lakes in a ‘sea’ of land, alpine meadows or mountaintops surrounded by evergreen forests, and even in clumps of trees in the midst of a grassland.” Wilson’s thoughts perhaps best sum up the reasons why counting the Earth’s species may be impossible.

Source of Information : Green Technology Biodiversity (2010)