Biodiversity, short for biological diversity, refers to the variety of all living things and their interactions on Earth. It encompasses the variety and variability of life at the genetic, species, and ecosystem level. Biodiversity includes not only species we consider rare, threatened, or endangered but also every living thing, from humans to organisms we know little about, such as microbes, fungi, and invertebrates.

Biodiversity is important because it supports everything in nature that we need to survive, such as food, clean water, medicine, and shelter. Ecosystems provide crucial services such as pollination, seed dispersal, climate regulation, water purification, nutrient cycling, and control of agricultural pests. Biodiversity also holds value for potential benefits not yet recognized, such as new medicines and other possible unknown services. Biodiversity has cultural value to humans as well, for spiritual or religious reasons, for instance.

Biodiversity changes over time as extinction occurs and new species evolve. Scientists often speak of three levels of diversity: species, genetic, and ecosystem diversity. In fact, these levels cannot be separated. Each is important, interacting with and influencing others. Changes at one level can cause changes at other levels.

• Species diversity: This is the variety of species within a habitat or a region. Some habitats, such as rainforests and coral reefs, have many species. Others, such as salt flats or a polluted stream, have fewer. In Australia, more than 80% of plant and animal species are endemic, which means that they only occur naturally in Australia.

• Genetic diversity: This is the variety of genes within a species. Each species is made up of individuals that have their own particular genetic composition. This means a species may have different populations, each having different genetic compositions. To conserve genetic diversity, different populations of a species must be conserved. Genes are the basic units of all life on Earth. They are responsible for both the similarities and the differences between organisms.

• Ecosystem diversity: This is the variety of ecosystems in a region or on Earth. Ecosystems are made up of living organisms and their physical and chemical environments. They can be as small as a puddle or as large as the Amazon rainforest. Ecosystems can be natural or human-made.

In summary, biodiversity is the variety and variability of life on Earth, including genetic, species, and ecosystem diversity. It is important because it supports everything in nature that we need to survive and has cultural value to humans. Biodiversity changes over time as extinction occurs and new species evolve, and scientists often speak of three levels of diversity: species, genetic, and ecosystem diversity.