Extinction and its causes

Contents

• Definition of Extinction

• Importance of Biodiversity

• Causes of Extinction1. Habitat destruction

2. Introduced species

3. Hunting and fishing

4. Environmental change

5. Extinction of a species from a food web

• Direct examples of extinction: The Dodo and the Great Auk

• Indirect examples of extinction: – The Stephen’s Island Wren

– The Passenger Pigeon’s louse

• Conclusion

For references, see teacher’s manual

Extinction

• The disappearance of a species, either

globally or locally.

Can you think of any of

extinct animals?

Why care about extinction?

• Humans have caused

rates of extinction to

increase by 100-1000

times!

• Extinctions are quickly

causing a decline in

global biodiversity

What is biodiversity?

• Biodiversity is the

range of different

species in an area (or

worldwide)

• Some species lost

through extinctions

may have beneficial

features, such as

medicines or food

crops

Some examples of extinct

animals

The Woolly MammothThe DodoThe Sabre Toothed Tiger

Environmental changes lead to

extinctions

• Humans activity is currently the biggest

risk to the environment.

– Indirect causes:

Causes that don’t immediately create

extinctions, e.g. climate change

– Direct causes

Causes that will immediately cause the loss of

individuals from a population, e.g. hunting and

fishing

Causes of Extinction

1. Habitat destruction

2. Introduced species

3. Hunting and fishing

4. Environmental change

5. Extinction of a species from a food

web/chain

Habitat Destruction

• Humans are destroying

natural habitats for the

benefits of resources,

urbanisation and

agriculture.

• Deforestation –

Amazon rainforest

• Destruction of coral

reefs – side effect of

trawler fishing

• Species that are introduced to a habitat accidentallyor purposefully.

• Accidental:

– hitchhiking

• Intentional:

– Pets or food crops

Introduced species

Introduced species • Competition

– A new species may cause natives to have to

compete for resources (food, shelter).

• Predation

– New species may predate upon the native species.

(For example the Stephen’s Island Wren)

• Disease

– The new species may bring a disease to the native

habitat, a disease to which they are immune to, but

the native species are very vulnerable to. (For

example the Grey Squirrel)

Introduced species example:

the Stephen’s Island Wren• In the 19th century, a

lighthouse was built on the

remote island, “Stephen’s

Island”.

• The island was home to a

species of flightless bird,

only found on this island.

• The lighthouse keeper

brought a pet cat, which

predated on the vulnerable

birds

• The birds were extinct in the

island by 1894

Hunting and Fishing

• Human population

increase has lead to a

higher demand of food.

• Increase in

hunting/fishing rates

• Some animals are also

hunted for their fur or

ivory, for example.

The Dodo

The Great Auk

In the last 100 years, the

average temperature has

risen by 0.6°C

Climate change

Rises in sea

level and

changes in the

weather are

predicted

Climate change cont.

• CO2 is produced

naturally for example

through respiration

• Also through human

activity, e.g. burning

fossil fuels

• CO2 causes the

greenhouse effect,

and therefore global

warming•A correlation between CO2 and temperature has been

determined (other greenhouse gases are also involved)

Changes to the environment will put pressure on

species

To survive, the species will have to migrate to a

more suitable habitat….Or adapt to the changes in the environment

Food webs and chains

• Species interact through many ways, including predation

• Food webs and chains display predatory interactions

• Changes to populations at any species in the food web will affect all other species in the web

Species dependence on the

environment and other species

• Species depend upon many factors in the

environment to survive, and some also

depend upon other species for survival

• Environment

– Climate, habitat, minerals, water etc.

• Other species

– Food resources, protection, interactional

relationships (for example pollination)

The affect of a loss of a species on

the food web

What will

happen to one

species if

another

becomes

extinct?

The loss of a predator species

Extinction

Population increase

Population decrease

Population decrease

The loss of a prey species

Extinction

Population increase

Population decrease

or extinction

Disruption of interactional

relationships

• Some species depend on each other for

various reasons, e.g.:

– Some plants need bees for pollination

– Parasites require a host to feed from

• If one of the species is lost from this

interaction, the other species may suffer

greatly.

Example: The Passenger Pigeon

and its parasitic louse• The Passenger

Pigeon was driven to extinction by hunting and habitat destruction by 1914.

• The pigeon’s parasitic louse was only found on this species of pigeon, and so the extinction of the Passenger pigeon lead to the coextinction of the louse

The Passenger Pigeon

The Passenger Pigeon’s

parasitic louse

Take home messages

1. Extinctions threaten biodiversity

2. Causes of extinction are either direct or

indirect, humans currently have a large

influence in causing extinctions.

3. The main causes of extinction are:

Habitat destruction, introduced species,

hunting or fishing, climate change and

disruption of food chain networks.

• Human activity is

behind the main

causes of

extinction.

• Biodiversity will

keep decreasing if

we don’t act to stop

extinctions

• What will you do

about it?