Download 4.2.2-.4 Causes of Extinction

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Non-human causes of extinction:
 Volcanic events
 Ocean temperature change
 Sea level changes
 Meteorites
 Glaciations
 Global climate change
 Competition/predation
Human causes of extinction/loss of biodiversity HIPPO
Habitat destruction and fragmentation
Introduced species
Over consumption
Rates of Extinction:
= number of species becoming extinct per unit time.
 Rates of extinction are very difficult to estimate,
because we don't even know within an order of
magnitude how many species there are.
 Fossil records can reveal the average "lifetimes" of
species, or how long different classes of plants and
animals generally exist on the earth before going
 From this information, scientists can determine a
"background" rate of extinction, or the natural rate of
extinction without human intervention.
 Because of human intervention the Earth's species are
dying out at an alarming rate, up to 1,000 times faster
than their natural rate of extinction.
 By carefully examining fossil records and ecosystem
destruction, some scientists estimate that as many
as 137 species disappear from the Earth EACH DAY,
which adds up to an astounding 50,000 species
disappearing every year.
The Earth has experienced 5 MASS EXTINCTIONS
 Mammals average species lifespan 1 million years.
 With ~ 5,000 mammalian species the background extinction rate = 1 every 200
 In the past 400 years, though, 89 extinctions have been recorded, almost 45
times the natural rate.
 Over 50 of those
extinctions have
occurred in the past
 Rate = 100 times the
background rate!!
Extinction Rates over geological time
Middle Cambrian age (about 540 million years ago)
•The locality is special because
of the soft-bodied preservation
of a wide diversity of fossil
invertebrate animals.
•Period of great speciation.
Characteristics of vulnerable species
 Small population size - island species.
 Small population size - species with limited habitats.
 Extremely specialized species.
 Species with low reproductive potential.
 Species that require large territories.
 Species with limited dispersal ability.
Vulnerable species - continued
 Migratory species.
 Species that are economically valuable or hunted for
 Predators.
 Species that are vulnerable to pollution.
 Species that are incompatible with civilization.
 Tropical rainforests contain at least half of the Earth's species.
 Most species have evolved to inhabit very specialized niches in their
 When humans disrupt that environment, many species cannot survive.
 Because species depend on each other in a complicated web of relationships,
changing just one part of that web harms the entire ecosystem.
 This breakdown of rainforest ecosystems will likely lead to the disappearance of
up to 10% of the world's species within the next 25 years.
Rainforest continued
 The human species depends on the rainforest's millions of life forms for its
own existence  The genetic diversity found within the rainforests provides invaluable
additions to the gene pool which help maintain and improve domestic crops.
 Without a diversity of strains, crops become overly homogenous and
vulnerable to mass blight.
 Many medicines that we regularly use come from rainforest species.