Biodiversity

Section #2:Biodiversity at Risk

Extinctions

•changes in Earth’s climate & ecosystems have caused the extinction of about ½ the species on Earth

Mass Extinctions

•the loss of many species in a relatively short period of time

•it takes millions of years for biodiversity to rebound after a mass extinction

Mass Extinction Events Over Geologic Time

Current Extinctions

•scientists warn that we’re in the midst of another mass extinction

•between 1800 & 2100, up to 25% of all species on Earth may have become extinct

•primary cause = humans (this is different from the past)

Threatened & Extinct Species Worldwide

Species Prone to Extinctions

•species with small populations•species with limited habitats•species that migrate•species that need special

habitats•species that need lots of space• species that are exploited by

humans

Endangered vs. Threatened

•endangered species = a species that is like to become extinct if protective measures are not taken immediately

•threatened species = a species that has a declining population & is likely to become endangered if not protected

Endangered Florida Panthers

How Do Humans Cause Extinctions?

•human population growth that has lead to . . . –habitat destruction & fragmentation

–pollution– introduction of nonnative species

–over-harvesting of species

Habitat Loss

•we use more land to build homes & for harvesting resources

•this destroys & fragments the habitats for other species

•75% of extinctions occur because of habitat loss

Invasive Exotic Species

•a species that is not native to a particular region

•they are brought to an area where they never lived before

•exotic species can threaten native species that have no natural defenses

Invasive Exotic SpeciesFire Ant Mounds

Harvesting, Hunting, Poaching

•many countries now have laws to regulate hunting, fishing, harvesting, & wildlife trade to cut down on excessive loss of species

•not all threatened species are legally protected, especially in poorer countries where they might be a source of food, medicine, or income

Poaching

Pollution

•pesticides, cleaning agents, drugs, & other chemicals used by humans are making their way into food webs around the globe

•we often don’t know the long-term effects until its too late

Pollution

•bald eagles became endangered from the pesticide DDT (now illegal to use in the U.S. still manufactured here and sold around the world)

•the DDT caused a thinning in the eagle’s eggshells & the babies did not survive

Endemic Species

•species that are native to and found only with a limited area

•scientists often use the numbers of endemic species of plants as an indicator of overall biodiversity

Areas of Critical Biodiversity

•tropical rain forests•coral reefs•coastal ecosystems•islands

Tropical Rain Forests

•only cover a small % of the Earth’s land surface (<7%)

•biologists estimate that over ½ of the world’s species live in these forests

•most of these species have not been described

•unknown #s of species are disappearing as tropical rain forests are cleared for farming cattle grazing

Tropical Rain Forests

•the Amazon has had an influx of visitors, not only tourists, but also scientists who are searching for new species to create new products, especially drugs

•the Brazilian government has now claimed the right to tax or patent any genetic material harvested with in its borders

Coral Reefs

•only occupy a small fraction of the ocean, but contain the majority of biodiversity

•reefs provide millions of people with food, tourism revenue, coastal protection, sources of new chemicals

•some have placed a value of $375 billion per year

Coastal Ecosystems

•threatened by human activities, particularly development along waterways, filling in swamps and marshes

•too much pollution is becoming a bigger problem, these ecosystems act as a buffer zone but still have limitations

Islands

•often hold very distinct, but limited numbers of species

•most species have migrated from the mainland and then evolved into new species

•introduction of invasive exotic species can destroy the island’s species

Biodiversity Hotspots

•the most threatened areas of high species diversity around the world

•have high numbers of endemic species that are threatened by human activities

•most have already lost 70% of their original vegetation

•typical hotspots are tropical rainforests, coastal areas, & islands

Hotspots

Biodiversity in the U.S.

•areas = Florida Everglades, California coastal regions, Hawaii, Midwestern prairies, Pacific NW forests

•species = freshwater fishes, mussels, snails, crayfish, pine trees, sunflowers, birds

Endemic Species to the U.S.