483 Summary • The IUCN Red List has over 26,000 species identifi ed as endangered and categorized based on their level of endangerment. • Animals on the IUCN Red List are identifi ed as extinct species, extinct in the wild species, critically endangered species, endangered species, vulnerable species, near threatened species, and least concern species. • The US Fish and Wildlife Service also identifi es species as either endangered or threatened on the Federal Lists of Endangered Species. • A species must be on the Federal Lists of Endangered Species to receive protection under the Endangered Species Act. • The primary causes of extinction due to human activity include habitat loss, degradation, fragmentation, the introduction of invasive species, overharvesting, loss of genetic variation, unsustainable human population growth, and climate change. • Habitat degradation may be caused by factors such as pollution in the soil, water, or air, a change in water fl ow, or the killing or removal of a key species. • Habitat fragmentation may be caused by the human construction of structures, such as dams, roads, and housing subdivisions. • Invasive species introduced by humans commonly cause habitat destruction and degradation. • Genetic variation declines as the population declines. As the population decreases, organisms begin inbreeding, which leaves the species vulnerable to genetic mutations, lessens their disease resistance, and may lead to the development of physical disabilities. • Overhunting or overfi shing reduces the number of breeding animals and reduces the genetic variation among the remaining animals. • Methods and technology used to assess wildlife species and their habitats include DNA barcoding, remote sensing, quadrat analysis, mark-recapture, total counts, incomplete counts, indirect counts, random, systematic, and stratifi ed sampling, and assessing bioindicators. • Many species can be used as bioindicators that indicate a shift in the environment and are a precursor to greater problems. • Many zoos, wildlife reserves, botanic gardens, and other conservation organizations have captive breeding programs to raise animals or plants that have become rare in their native habitats. • A species survival plan is an initiative by the Association of Zoos and Aquariums to share animals for breeding to spread genetic variation. • In order to protect plant and animal wildlife, the United States government has developed legislation to prevent the import, export, and injury to species that are considered at risk. These laws are enforced by various agencies, such as the US Fish and Wildlife Service, US Forest Service, and National Park Service.