Threats to biodiversity

Over-exploitation

This causes the numbers of a population to become dangerously low

Example: over-exploitation

Overfishing - as the development of bigger nets and more sophisticated sonar increases, the populations of fish species has started to deplete to such a low level that the continued exploitation of these species is no longer sustainable

What five things can be done to stop the depletion of fish stocks and recover their populations?

• Control the number of boats

• Quotas

• Reduce hours at sea

• Restrict areas where fishing is permitted

• Strict regulations

• Use nets with larger holes to allow smaller fish to swim through

Bottleneck effect

When a significant percentage of a population has been wiped out the surviving small population may have lost some of its genetic variation

Diagram: bottleneck effect

What two things can cause a population to be wiped out?

Natural disasters like a fire or a flood, or human activity like deforestation or over-hunting

What two problems can occur when there is a loss of genetic diversity?

Inbreeding and poor reproductive rates, and the population might not survive environmental changes

What causes habitat loss by fragmentation?

The clearing of habitats (deforestation)

What does the process of fragmentation of a habitat result in?

The formation of several habitat fragments whose total surface area is less than that of the original habitat

What do habitat fragments suffer from?

Degradation at their edges which may further reduce the habitats size

What does habitat loss by fragmentation result in?

An increase in competition between species, causing a decrease in biodiversity as more isolated fragments and smaller fragments exhibit a lower species diversity

What is one way of helping habitat loss by fragmentation?

Habitat corridors

In what three ways do habitat corridors help habitat loss by fragmentation?

• Increased access to a choice in mate

• Increased access to food

• Increased chance of recolonisation of small fragments after local extinctions

Diagram: habitat fragmentation

Example: habitat loss by fragmentaiton

Tigers - 95% of tigers were wiped out due to over-hunting and to combat this habitat corridors have been introduced to encourage breeding

Introduced species

Non-native species that humans have moved, accidentally or intentionally, to a new geographical location

Naturalised species

Introduced species that have become established in wild communities

Invasive species

Naturalised species that have spread rapidly and eliminated native species, therefore reducing species diversity

Why are some invasive species successful?

They are free of their natural enemy/pathogen/parasite and competitors which limited their population in their native habitat

What three things might invasive species do to native species?

• Hybridise with them

• Prey on them

• Out-compete with them for resources

Example: an invasive species

Giant hogweed - their sap is poisonous, causing blistering and burning of the skin