Biodiversity is the variety of all the different species of organisms on Earth, or within an ecosystem. A rainforest has a very high biodiversity because it contains a huge number of different plant, animal and microorganism species. A field of one crop has a low biodiversity.
A great biodiversity keeps an ecosystem stable. When there are many species, each one depends less on any single other species for food, shelter and the maintenance of the physical environment. If one species declines, others can fill the gap, so the whole ecosystem is not harmed. In an ecosystem with few species, the loss of one organism can cause others to die out.
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.