Species diversity

Species diversity refers to the variety of different types of living things on Earth, such as bacteria, fungi, insects, mammals, plants and more. Different species have different roles to play within ecosystems. To remain healthy, most ecosystems require thousands of different species making up their food webs.

A species can be defined as a group or population of similar organisms that reproduce by interbreeding within the group. Members of a species do not normally reproduce with members of any other species.

Human beings, for example, belong in a single species — Homo sapiens. Although there are different populations of humans, with different characteristics in different parts of the Earth, they can all successfully interbreed with each other and produce normal offspring. So, even though no two human beings are exactly alike, humans make up a single species because they reproduce among themselves.

All the different breeds of dogs, from Great Danes to Chihuahuas, belong in a single species, because they can interbreed and produce fertile offspring. Dogs and foxes, however, are different species because they can't interbreed.

Similarly, all horses belong in one species because they can interbreed. But horses and donkeys are different species because, although they can interbreed, their offspring (mules) are sterile.

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