On this page:
Introduction What Is Biodiversity? Genetic Diversity Species Diversity Ecosystem Diversity Why Does Biodiversity Matter? Ecosystem Services Ecological Stability Intrinsic Value Measuring Biodiversity Distribution of Biodiversity Threats to Biodiversity Conservation of Biodiversity
There are approximately 8 to 10 million species of living organisms on Earth. Scientists have formally described only about 2 million of them. In a single hectare of tropical rainforest, there may be more species of insects than in the entire continent of Europe. A teaspoon of healthy soil contains billions of bacteria representing thousands of species.
This extraordinary variety of life is biodiversity. And it is disappearing at a rate that scientists describe as the sixth mass extinction in Earth's history, this time caused not by an asteroid or volcanic eruption but by human activity.
Biodiversity is the variety of life on Earth at all levels of biological organization.
It encompasses three distinct dimensions.
Genetic diversity is the variation in DNA sequences among individuals within a species.
Genetic diversity within a population means that different individuals have different alleles for many genes. This variation arises from mutations, sexual reproduction, and gene flow between populations.
High genetic diversity provides a population with greater capacity to adapt to changing conditions. If a disease arrives or the environment changes, some individuals with particular alleles may be better able to survive. Low genetic diversity leaves a population vulnerable.
Small, isolated populations tend to have low genetic diversity due to inbreeding and genetic drift, making them particularly vulnerable to extinction.
Species diversity is the variety of different species in an area. It includes both the number of species (species richness) and the relative abundance of each species (species evenness).
A community with many species all at roughly equal abundances has higher species diversity than a community with many species but dominated by just one or two.
Ecosystem diversity is the variety of different ecosystems and habitats on Earth. Tropical rainforests, coral reefs, tundra, deep ocean floors, freshwater wetlands, and temperate grasslands are all distinct ecosystem types, each supporting a unique community of species.
Biodiversity has value at multiple levels.
Biodiversity underpins the functioning of ecosystems, which provide services essential to human welfare.
Ecosystems with higher biodiversity are generally more stable and resilient. More species means more ecological pathways. If one species declines, others can partially compensate. A diverse ecosystem absorbs disturbances that would collapse a simpler one.
Many argue that species have intrinsic value regardless of their utility to humans. Each species represents millions of years of evolution and an irreplaceable part of the history of life.
Biodiversity is measured using several indices.
The Simpson's Diversity Index takes into account both the number of species and the relative abundance of each, giving a more complete picture of diversity.
D = 1 - [Σn(n-1) / N(N-1)]
Where n is the number of individuals of each species and N is the total number of all individuals. A value close to 1 indicates high diversity. A value close to 0 indicates low diversity.
Biodiversity is not evenly distributed across the planet.
Tropical regions have the highest biodiversity. Tropical rainforests cover less than 6 percent of Earth's surface but contain over half of all species. The stable, warm, wet climate, high productivity, and long evolutionary history of tropical regions all contribute to their exceptional species richness.
Coral reefs support approximately 25 percent of all marine species despite covering less than 1 percent of the ocean floor.
Biodiversity hotspots are regions with exceptionally high species richness and endemism (species found nowhere else) that face severe threats. The hotspot concept, developed by Norman Myers, identifies 36 areas that together support over half of all plant species and 43 percent of bird, mammal, reptile, and amphibian species, all in areas that have lost at least 70 percent of their original habitat.
Biodiversity is currently declining at a rate unprecedented since the mass extinction that killed the non-avian dinosaurs 66 million years ago.
Habitat destruction is the single greatest threat to biodiversity globally. Deforestation, conversion of land for agriculture, drainage of wetlands, and urban expansion eliminate the environments species depend on.
Habitat fragmentation divides continuous habitats into isolated patches too small to support viable populations of many species.
Species introduced to new areas by human activity can devastate native species through predation, competition, or disease. Islands are particularly vulnerable because native species have often evolved without exposure to mainland predators.
Overhunting, overfishing, and unsustainable collection of wild plants and animals have driven many species to extinction or near-extinction. The passenger pigeon, hunted to extinction in 1914, and the current decline of many shark species from overfishing are well-documented examples.
Rising temperatures, changing rainfall patterns, and ocean acidification are altering habitats faster than many species can adapt or migrate. Coral bleaching driven by warming oceans threatens coral reef ecosystems globally.
Pesticides, industrial chemicals, plastics, and nutrient pollution (eutrophication) damage ecosystems and kill sensitive species throughout food chains.
Conservation biology addresses the threats to biodiversity through several approaches.