3.3 Threats to Biodiversity

Threats to Biodiversity p.100

Habitat Loss and Deforestation p.101

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.

Draining of Wetlands p.102

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.

Alien and Invasive Species p.102

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.

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).

Overexploitation p.104

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%

Disrupting Connectivity Across

Ecosystems p.105

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.

Extinction Reduces Biodiversity p.106

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.

Current Extinction Rates p.108

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.