Biodiversity refers to the variety of life at all levels of biological organization, including genetic diversity, species diversity, and ecosystem diversity. Species richness is the total number of different species present in an ecological community, while species evenness describes how equally abundant each species is within a community; high evenness means species have similar population sizes. Biodiversity is important because it provides ecosystem services such as pollination, water purification, nutrient cycling, climate regulation, and resilience against environmental disturbances. Areas of exceptionally high biodiversity under threat are designated as biodiversity hotspots, biogeographic regions with at least 1,500 endemic plant species that face destruction.
Many threats to biodiversity originate from human activities. The main cause of current biodiversity loss is habitat destruction driven by deforestation, urbanization, and agricultural expansion. Habitat fragmentation divides large, continuous habitats into smaller, isolated patches, reducing biodiversity and disrupting wildlife movement. Invasive species, which are non-native organisms that spread rapidly and cause ecological or economic harm when introduced to a new environment, further threaten native species. The IUCN Red List is the world's most comprehensive inventory of the global conservation status of biological species, classifying them from Least Concern to Extinct. An endangered species faces a very high risk of extinction in the wild in the near future, while a threatened species is likely to become endangered in the foreseeable future. Endemic species, those found naturally only in a specific geographic area and nowhere else, are particularly vulnerable to habitat loss.
Conservation biology is the scientific study of the nature and status of Earth's biodiversity, aimed at protecting species, habitats, and ecosystems from excessive extinction. In-situ conservation protects species within their natural habitats through methods like national parks, wildlife sanctuaries, and marine protected areas. Ex-situ conservation preserves species outside their natural habitats in zoos, botanical gardens, seed banks, or captive breeding programs. Biosphere reserves are internationally recognized areas designated under UNESCO's Man and the Biosphere Programme to promote sustainable development. Other conservation strategies include rewilding, which restores ecosystems by reintroducing native species and removing invasive species, and protecting umbrella species whose conservation indirectly protects many other species that share their habitat. The Convention on Biological Diversity, an international treaty adopted in 1992, aims to conserve biological diversity, promote sustainable use of its components, and ensure fair sharing of genetic resource benefits.