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3.3 Threats to Biodiversity
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Threats to Biodiversity p.100
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Habitat Loss and Deforestation p.101
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Habitat Loss and Deforestation p.101
Habitat loss:
destruction of habitats
usually results from human activities (deforestation)
Deforestation:
results from clearing forests for logging or other human uses and never replanting them.
Natural sources of habitat destruction:
volcanic eruptions, wildfires, droughts, and severe storms eg. hurricanes.
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Draining of Wetlands p.102
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Draining of Wetlands p.102
another major cause of habitat loss
Wetlands
~ 6% of Earth’s surface
~ 24% of the world’s wetlands are in Canada.
Plants, turtles, snakes, minks, and thousands of
other organisms live in wetlands.
often drained for farming or for building homes
and other buildings.
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Alien and Invasive Species p.102
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Alien and Invasive Species p.102
Alien species:
accidentally or intentionally introduced into a
new location
Most are either harmless or beneficial
sometimes invasive
Invasive species:
can take over the habitats of native species or
invade their bodies
upset the equilibrium of an ecosystem, causing
problems for native species.
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Alien and Invasive Species p.102
Examples
round goby
competes with native fish for spawning areas
eats their eggs
Zebra mussels
decline of small crustaceans (food of many fish).
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Overexploitation p.104
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Overexploitation p.104
use or extraction of a resource until it is depleted
Threatens biodiversity
Examples:
Overhunting: passenger pigeon (disappeared in
1900s)
Overfishing: Atlantic cod and yellowfin tuna
reduced by 90%
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Disrupting Connectivity Across
Ecosystems p.105
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Disrupting Connectivity Across
Ecosystems p.105
Species are interconnected and often rely on each other
decline in one species can lead to reductions in the
carrying capacity and biodiversity
Salmon populations in British Columbia:
Affects the health of bear, wolf, eagle and crow
populations.
Up to 70% of the nitrogen in plants, trees, insects,
birds, and bears in the temperate rainforest ecosystem
comes from the Pacific Ocean via the salmon.
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Extinction Reduces Biodiversity p.106
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Extinction Reduces Biodiversity p.106
Extinction:
all the individuals of a species have died
both terrestrial and aquatic ecosystems
Throughout the entire history of life on Earth
to avoid extinction and maintain a stable population:
birth rate = death rate, over a long period of time.
Two patterns of natural extinction:
Background extinction is apparent over long
periods of time as ecosystems gradually change.
Mass extinction results from a relatively sudden
change to Earth’s ecosystems.
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Current Extinction Rates p.108
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Current Extinction Rates p.108
Estimate 100 to 1000 times higher than a normal
background rate.
a biodiversity crisis.
resulted from human activities:
Deforestation
habitat destruction
air and water pollution changing the abiotic and biotic conditions in ecosystems.