Biodiversity is the variety of all the different species of organisms on Earth, or within one ecosystem. A tropical rainforest has a very high biodiversity because so many species of plants, animals and microorganisms live there. A field where only one crop is grown has a low biodiversity.
A great biodiversity ensures the stability of an ecosystem. When there are many species, each one depends less on any single other species for food, shelter and the maintenance of the physical environment. Great biodiversity reduces the dependence of one species on another. If one species declines, the others can cope, so the ecosystem stays stable. In an ecosystem with few species the loss of one organism can cause others to die out, so the ecosystem is less stable.
The future of the human species on Earth relies on us maintaining a good level of biodiversity. Many human activities are reducing biodiversity, and only recently have measures been taken to try to stop this reduction. Waste, deforestation and global warming all have an impact on biodiversity, and you meet each of them in the next lessons.