Facts about Threatened Species

How many species are threatened?

• 16,119 species are threatened with extinction, but this may be a gross underestimate because fewer than 3% of the world’s 1.9 million described species have been assessed by the Red List.
• Animals: 7,725
• Plants and lichens: 8,394
• In major species groups, the percentage of threatened species ranges between 12% and 52%.
• Birds: 12% or 1 in 8
  Mammals: 23% or 1 in 4 are threatened.
• Amphibians: 32% or 1 in 3.
• Turtles and tortoises: approximately 42%
• Conifers: 25% or 1 in 4
• Cycads (an ancient group of plants): 52%

What are the threats?

• 99% of threatened species are at risk from human activities. Humans are the main cause of extinction and the principle threat to species at risk of extinction.
• Habitat loss and degradation are the leading threats. They affect 86% of all threatened birds, 86% of the threatened mammals assessed and 88% of the threatened amphibians.
• Introductions of alien species. Some of the worst include. cats and rats, green crabs, zebra mussels, the African tulip tree and the brown tree snake. Introductions of alien species can happen deliberately or unintentionally, for example, by organisms "hitch-hiking" in containers, ships, cars or soil.
• Over-exploitation . Resource extraction, hunting, and fishing for food, pets, and medicine threatens many species.
• Pollution and disease .
• Human-induced climate change is increasingly recognised as a serious threat. Climate change is altering migratory species patterns, causing coral bleaching, etc.

Which species are threatened by what?

• Mammals: 33% are threatened by over-exploitation.
• Birds: 30% are threatened by over-exploitation and invasive alien species. Invasives are impacting 67% of threatened birds on islands.
• Amphibians: 29% are affected by pollution (including climate change) and 17% by disease (particularly chytridiomycosis). The interaction between disease and extreme climatic events (drought) is the leading hypothesis for widespread amphibian declines.
• Marine species: Primarily threatened by over-exploitation and habitat loss. Incidental mortality as a result of fisheries is an increasing threat, affecting seabirds, marine mammals, and other marine species.
• By-catch from fisheries threatens 83 bird species.
• Freshwater species are most threatened by habitat loss, followed by pollution and invasive species.
• Threat processes are dynamic and change over time. Invasive alien species were historically the greatest threat to birds, but today, habitat loss has emerged as the dominant threat. This may change again if predictions of global warming are correct.

Where are the most species threatened?

• In the tropics, especially on mountains and on islands.
• While the vast majority of extinctions since 1500 AD have occurred on oceanic islands, over the last 20 years, roughly 50% of extinctions occurred on continents.
• Central and South America; Africa south of the Sahara; and tropical South and Southeast Asia. Why? These are the tropical continents that contain the tropical and subtropical moist broadleaf forests that are believed to host the majority of the earth’s terrestrial and freshwater species.
• Australia , Brazil, China, Indonesia, and Mexico have both a high number of threatened and threatened endemic species.
• Threatened marine mammals are concentrated in the Northern Pacific Ocean.
• Threatened seabirds, chondrichthyan fishes (sharks, rays and chimaeras) and seahorses (the latter two not completely assessed) are especially threatened in the eastern Indian Ocean and southwest and west-central Pacific.

What are the trends?

• The number of threatened species is increasing in almost all the major taxonomic groups.
• Since 1994 the number of bird species threatened with global extinction has risen to 12%.
• Red List Indices for birds and amphibians show that the status of both has declined steadily since the 1980s.
• How are trends measured? The Red List Indices (RLIs) are an important new development which measure trends in extinction risk by comparing the status of specific groups of species over time. RLIs can only be calculated for species groups that have been fully assessed at least twice, so they are only available for certain groups. Red List Indices are currently available for birds and amphibians.

What is extinction?

• The Red List considers a species extinct when exhaustive surveys in known or expected habitats fail to record any individuals.
• The IUCN Red List documents 784 extinctions and 65 extinctions in the wild since 1500AD (when historical scientific records began), but this number doesn’t account for the thousands of species that go extinct before scientists even have a chance to describe them.
• Previous extinctions were due to natural causes. Extinction is actually a natural phenomenon that we expect to occur at a rate of approximately 1 to 5 species per year, but nowadays experts believe we are losing dozens per day – that’s roughly 100 to 1000 times higher than background rates!
• Current extinctions are generally brought about by humans. Extinctions caused by humans are considered to be a recent phenomenon: today 99% of threatened species are at risk from human activities.

BIODIVERSITY GLOSSARY

• Biological diversity: “biodiversity” means the variability among living organisms from all sources including, inter alia, terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part; this includes diversity within species, between species and of ecosystems.
• Biome : major ecological community, a division of the world's vegetation that corresponds to a particular climate and is characterized by certain types of plants and animals, for example, tropical rain forest or desert.
• Ecosystem : a dynamic complex of plant, animal and micro-organism communities and their non-living environment interacting as a functional unit.
• Endemic : restricted to a particular area: used to describe a species or organism that is confined to a particular geographical region, for example, an island or river basin.
• Genus, Genera pl. : set of closely related species: a category in the taxonomic classification of related organisms, comprising one or more species. Similar genera are grouped into families.
• Habitat : the place or type of site where an organism or population naturally occurs.
• Invasive alien species: are those that occur outside their natural range and threaten the existence of native plants and animals.
• Taxon : category of organisms, any of the groups to which organisms are assigned according to the principles of taxonomy, including subspecies, species, genus, family, order, class, and phylum.