Biodiversity is the variety of life.

It can be studied on many levels. At the highest level, one can look at all the different species on the entire Earth. On a much smaller scale, one can study biodiversity within a pond ecosystem or a neighborhood park. Identifying and understanding the relationships between all the life on Earth are some of the greatest challenges in science.

Most people recognize biodiversity by species—a group of individual living organisms that can interbreed. Examples of species include blue whales, white-tailed deer, white pine trees, sunflowers, and microscopic bacteria that can't even be seen by the naked eye. Biodiversity includes the full range of species that live in an area.

Biodiversity at a Glance

American bullfrog, Harrisburg, PA

Pretend you're taking a look at the species biodiversity within a local pond. At first glance, we can identify different plants, including cattails and water lilies. If we wait a while, we might be able to spot a garter snake, a bullfrog, or maybe a red-winged blackbird. With a closer look, we can see invertebrates and worms under leaves, on grasses and in the pond water.

Think you’re done? You have not even scratched the surface of the biodiversity within the pond. Using a microscope, we would be able to see hundreds or even thousands of different bacteria that inhabit the pond water. They're all part of the species biodiversity of this small ecosystem.

More than Just Species

Species diversity is only one part of biodiversity. To properly catalogue all the life on Earth, we also have to recognize the genetic diversity that exists within species, as well as the diversity of entire habitats and ecosystems.

Genetic biodiversity is the variation in genes that exists within a species. A helpful way to understand genetic diversity is to think about dogs. All dogs are part of the same species, but their genes can dictate whether they are Chihuahua or a Great Dane. There can be a lot of variation in genes—just think about all the colors, sizes, and shapes that make up the genetic diversity of dogs.

Ecological biodiversity is the diversity of ecosystems, natural communities, and habitats. In essence, it’s the variety of ways that species interact with each other and their environment. The forests of Maine differ from the forests of Colorado by the types of species found in both ecosystems, as well as the temperature and rainfall. These two seemingly similar ecosystems have a lot of differences that make them both special.

Five Facts on Biodiversity

1. Researchers have estimated that there are between 3 and 30 million species on Earth, with a few studies predicting that there may be more than 100 million species on Earth.

2. Currently we have identified only 1.7 million species, so we have a long way to go before we can come close to figuring out exactly how many species are on Earth.

3. There is more biodiversity within tropical ecosystems than temperate or boreal ecosystems. In fact, tropical rain forests have the most diversity.

4. The most diverse group of animals are invertebrates. Invertebrates are animals without backbones, including insects, crustaceans, sponges, scorpions, and many other kinds of organisms.

5. Over half of all the animals already identified are invertebrates. Of these, beetles are some of the most numerous species.

Biodiversity's Importance

Biodiversity is extremely important to people and the health of ecosystems. Biodiversity allows us to live healthy and happy lives. It provides us with an array of foods and materials, and it contributes to the economy. Without a diversity of pollinators, plants, and soils, our supermarkets would have a lot less produce.

Most medical discoveries to cure diseases and lengthen life spans were made because of research into plant and animal biology and genetics. Every time a species goes extinct or genetic diversity is lost, we will never know whether research would have given us a new vaccine or drug.

Biodiversity is also an important part of ecological services that make life livable on Earth. They include everything from cleaning water and absorbing chemicals, which wetlands do, to providing oxygen for us to breathe—one of the many things that plants do for people.

Biodiversity allows for ecosystems to adjust to disturbances like fires and floods. Genetic diversity even prevents diseases and helps species adjust to changes in their environment.

Threats to Biodiversity

Extinction is a natural part of life on Earth. Over the history of the planet, most of the species that ever existed evolved and then gradually went extinct. Species go extinct because of natural shifts in the environment that take place over long periods of time, such as ice ages.

Today species are going extinct at an accelerated and dangerous rate because of non-natural environmental changes caused by human activities. Some of the activities have direct effects on species and ecosystems, such as habitat loss and degradation, overexploitation (such as overfishing), and the spread of non-native species and diseases. Some human activities have indirect but wide-reaching effects on biodiversity as well, including climate change and pollution.

All of these threats have put a serious strain on the diversity of species on Earth. According to the International Union for Conservation of Nature (IUCN), globally about one third of all known species are threatened with extinction. That includes 29 percent of all amphibians, 21 percent of all mammals, and 12 percent of all birds. If we do not stop the threats to biodiversity, we could be facing another mass extinction with dire consequences to the environment, and human health and livelihood.

International Union for Conservation of Nature
Comparing and Graphing Nine Environmental Threats, Researchers Find Unexpected Evils, Popular Science
Encyclopedia of Earth: Biodiversity
World of Biology. McGrath, Kimberley A., ed. The Gale Group, Farmington Hills, MI: 1999.
Precious Heritage: The Status of Biodiversity in the United States. Stein, Bruce A., Lynn S. Kutner and Jonathan S. Adams. Oxford University Press, New York: 2000
US Forest Service: Ecoregions of the United States

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