Species in Tropical Forests

Closed tropical forests contain more than half of the world's species, though they cover only 7 percent of the earth's land surface. The relative species richness of the tropical forest biome varies with the group of species involved, and for some taxa, scientific knowledge of species richness is limited.

Plants

The most complete information available is on plant species. The neotropics contain an estimated 86,000 species of vascular plants, tropical and semi-arid Africa contains 30,000 species, Madagascar contains 8,200, and tropical Asia, including New Guinea and tropical Australia, account for 45,000 species. In all, tropical regions support two thirds of the world's approximately 250,000 species of vascular plants. Norman Myers estimated that two thirds of all tropical plant species are found in moist tropical forests (evergreen or deciduous closed forest), and data provided by Alwyn Gentry support this estimate. Accordingly, about 45 percent of the world's vascular plant species occur in closed tropical forests.

Vertebrates

The percentage of terrestrial vertebrates found in tropical forests compares with that of plants. An estimated 2,600 avian species--1,300 species in the neotropics, 400 in the afrotropics, and 900 in tropical Asia--depend on tropical forests. This count amounts to roughly 30 percent of the estimated global total. The percentage is lower than for plants, but it does not include avian species that occur in the tropical forest but are not completely dependent upon it. Bruce Beehler notes that fully 78 percent of New Guinea's nonmarine birds occur in rainforests, though many of these may survive in other habitats as well.

Invertebrates

Among invertebrates, substantial uncertainty exists over the relative abundance of species in tropical forests. Until recently, the relative diversity of arthropods in the tropics as compared to the temperate zone was expected to be similar to that of better known groups, such as vascular plants or birds. However, Terry Erwin's discovery of a tremendous richness of beetle species in the canopy of a moist tropical forest suggests that the relative richness of arthropods in the tropics is much greater. As many as 30 million arthropod species--up to 96 percent of the world's total for all species--may exist in tropical forests.

Percentage of World's Species

The fraction of the entire world's species that occur in tropical forests can't be accurately estimated because the total number of species in several potentially large taxonomic and ecological groups--including insects, nematodes, and bottom-dwelling marine invertebrates--is unknown. However, half of all vertebrates and vascular plant species occur in tropical forests and if the tremendous species richness of arthropods in this biome is any indication, at least 50 percent--and possibly as much as 90 percent--of the world's total species are found in closed tropical forests.