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