Biodiversity at Risk
10.2 pages 245-251
Extinctions
• There have been 5 mass extinctions on Earth
– Mass extinction is when multiple species disappear in a short period of time
– Currently in a 6th mass extinction mostly caused by humans
Species Prone to Extinction
• The following put species at risk for extinction
– Species with already small populations
– Species that migrate
– Species that need large or specialized habitats
– Species exploited by humans
How do Humans Cause Extinction?
• As the human population grows so does the rate of extinction
– Major causes of extinction by humans
– Destruction of habitat
– Introduction of invasive species (exotic)
– Pollution
– Overharvesting of species
Habitat Destruction
• Habitat loss causes 75% of the extinctions on Earth
– As the population of humans grows so does the need for resources and vacant land for
buildings.
– Habitat destruction is the number one cause of extinction
– Example: the Florida Panther on verge of extinction as the Everglades shrink
– Only 150 wild Florida panthers roam east of Mississippi River
Invasive (exotic) species
• The introduction of invasive species to an area causes the extinction of native species
• Invasive species are successful because:
– Do not have natural predators in new area
– Adapt to the new conditions and thrive
– Take over valuable resources from the native species
Hunting, Harvesting, and Poaching
• Unregulated hunting in the 1800-1900’s in the U.S. caused the extinction of the passenger
pigeon
– Brought the North American bison to extremely low levels that they are just now
recovering from
– Destroyed the Pacific Coast kelp beds with the over hunting of otter.
• Thousands of rare species are hunted, harvested, and poached for pets, trophies, plants, food,
and medicine.
Pollution
• Pesticides, cleaning agents, drugs, and chemicals used by humans find there way into
ecosystems via food webs.
• Causes food webs to break down and loss of species diversity
Areas of Critical Diversity
• Endemic species are used to measure the amount of biodiversity in an area
– Tropical rain forests
• Cover less than 7% of Earth’s land surface (31.5 million acres destroyed a year).
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50% of world’s species live in the rain forests
Native tribes in the rain forest still practice old ways of living off the land
YanomamÖ
• Live in the Amazon-native tribal people
• Were discovered in 1730 by Spanish explorers
– Use poison dart frogs skin on their arrows during warfare.
– Use plants and fungi as food and medicine
– Animals local for food
– Rainforest meets all their needs
Coral Reefs and Coastal Ecosystems
• Coral reefs are a small fraction of the marine environment but has the most biodiversity
– Provide food
– Protect coast lines from waves and floods
• 60% of coral reefs are threatened due to human activities:
– Over fishing
– Pollution
Biodiversity Hotspots
• Hotspots have the most threatened species
• There are 35 hotspot areas worldwide
• Most have lost 70% of their original vegetation
• Most hotspots are tropical rain forests, coastal areas, and islands.
Madagascar
• Only 18% of original forests remain
• 80% of the 10,000 flowering plants are endemic
• 91% of 300 species of reptiles are endemic
• All 33 species of Lemur (1/10 of all primate species) live here
Biodiversity in the U.S.
• Wide variety of unique ecosystems
– Florida Everglades
– California Coastal region
– Hawaii
– Great Plains prairies
– Pacific Northwest forests
California Floristic Province
• Home to:
– 3488 native plants (2124 are endemic and 565 are threatened or endangered)
• Causes:
– Use of land for agriculture and housing
– Dam construction
– Overuse of water
– Destructive recreation
– mining