Biodiversity at Risk

Mass Extinction  Extinction of many species in a relatively short period of time  The current mass extinction is different because humans are the primary cause of the extinctions

Species Prone to Extinction  Species more at risk include those that migrate, those that need large or special habitats, and those that are exploited by humans  Endangered species: likely to become extinct if protective measures are not taken  Threatened species: has a declining population and is likely to become endangered if it is not protected

How Do Humans Cause Extinctions?  Habitat Destruction and Fragmentation  As the human population grows, we use more land to build homes and harvest resources  Causes almost 75% of extinctions now occurring

How Do Humans Cause Extinctions?  Invasive Exotic Species  Species that is not native to a particular region  Threaten native species that have no natural defenses against them

How Do Humans Cause Extinctions?  Harvesting, Hunting, and Poaching  Rare species are harvested and sold for use as pets, houseplants, wood, food, or herbal medicine  Many countries have laws to regulate hunting, fishing, harvesting, and trade of wildlife  Poaching: the illegal harvesting of fish, game or other species

How Do Humans Cause Extinctions?  Pollution  Pesticides, cleaning agents, drugs, and other chemicals get into food webs  Long term effects may not be clear for many years

Areas of Critical Biodiversity  Endemic species: species that are native to and found only within a limited area  Often used as an indicator of biodiversity because plants form the basis of ecosystems on land

Areas of Critical Biodiversity  Tropical Rain Forests  Over half of the world’s species  Most never described  Species disappearing as forests are cleared for farming or cattle grazing

Areas of Critical Biodiversity  Coral Reefs and Coastal Ecosystems  Occupy a small fraction of marine environments, but contain the majority of the biodiversity there  Provide millions of people with food and tourism revenue  Protect coasts from waves and are sources of new chemicals  Not well protected  Threatened by overfishing and pollution

Areas of Critical Biodiversity  Islands  Colonizing species may evolve into several new species  Hold limited sets of species  Many species become endangered by competition from exotic species

Areas of Critical Biodiversity  Biodiversity Hotspots  The most threatened areas of high species diversity  25 areas identified by international conservationists  Mostly tropical rainforests, coastal areas and islands

Areas of Critical Biodiversity  Biodiversity in the United States  U.S. includes a wide variety of unique ecosystems  Unusually high numbers of species of freshwater fishes, mussels, snails, crayfish, land plants like pine trees and sunflowers