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Biodiversity Loss and Species
Extinction vs. Extirpation
• Extinction occurs when the last member of
a species dies and the species ceases to
• Extirpation is the extinction of a particular
population from a given area, but not the
entire species globally. (ex. Tiger)
• Extirpation often leads to extinction
Extinction is “natural”
• Imagine a world today with dinosaurs, trilobites,
ammonites, etc. – there would be no room for
• 99% of the species that ever lived are already
extinct. Only about 1% of the species today are
those that have ever existed.
• Background rate of extinction: rate of extinctions
that occurred before humans. Approximately
one species every 500-1,000 years
Mass Extinction
• 5 times in the last 440 million years, the
extinction rate has been much higher than
the background rate.
A Sixth Mass Extinction?
• Humans have set the stage for a 6th mass
extinction based on the current extinction
rate – 30,000 species face extinction and
~1100 have gone extinct in 400 years
• Poaching is a controversial issue in African
and Asian nations, as the products (tusks,
skins, etc.) are the livelihood of some of
the poor in these countries. However,
poaching also leads to extirpation and
sometimes extinction of those species.
Compare and contrast the positive and
negative aspects of poaching and come to
a conclusion as to whether poaching
should continue or not.
5 Reasons for Species Loss:
• Habitat alteration
• Invasive Species
• Pollution
• Population Growth
• Overexploitation
Habitat Alteration
• Agriculture removes food, shelter and
other resources for wildlife
• Hydroelectric power alters water
• Urbanization and suburban sprawl
• Global climate changes (global warming)
• Primary source of population declines
• Can benefit a few species (pigeons)
Invasive Species
• Non-native species that spreads widely and
rapidly, out competing the natural species of that
• Transported by ships, planes, animal trade,
seeds, human immigrants bringing their native
plants/animals, purposely for aesthetics,
economic reasons
• Without predators and with unlimited resources,
species flourish and take over
• ex. Brown tree snake
Brown Tree Snake as an Invasive
• Transported in cargo
on ships and planes
during WWII
• Native to Solomon
Islands, New Guinea,
• Invasive in Guam
• Have destroyed the
populations of 12
native birds to Guam
• Air pollution degrades
forest ecosystems
• Water pollution affects fish
and amphibians
• Agricultural runoff can harm
terrestrial and aquatic
• Toxic chemicals and oil
have greatly affected
species in recent years
Population Growth
• More people mean more habitat alteration,
more pollution, more overexploitation,
more invasive species, more resource
consumption, etc.
• Ultimate reason behind the threats to
• Overharvesting of species and
overconsumption of resources
• Poaching in the grasslands of
Africa and Asia have greatly
depleted the species of animals
– tigers, antelope, elephants
• Consumption of paper products
leads to increased need for
logging, decreasing number of
trees and in the long run,
causing global warming (CO2