The disappearance and fragmentation of habitats due to human activities - deforestation and the draining of wetlands for agriculture, urbanization, and the establishment of industries - poses the greatest threat to animal and plant species.

Other threats include overexploitation (overfishing and too intensive hunting) and pollution. Also, alien species introduced by humans can pose a threat. Furthermore, climate change is playing an increasingly significant role.

The IUCN Red List (International Union for Conservation of Nature) includes 26,197 species of threatened animals and plants, of which more than 8000 vertebrate species are vulnerable, endangered, or critically endangered (2386 fish, 2100 amphibians, 1469 birds, 1215 reptiles, and 1204 mammals).