1. Unit 3 3.8- Threats to Biodiversity
Higher Biology
Unit 3
3.8- Threats to Biodiversity

2. Overexploitation
To exploit a natural resource is the make the best use of it
To over exploit a resource means to use it up at a rate that is not sustainable
A common example of overexploitation is overharvesting or overfishing
Overharvesting and overfishing depletes species numbers to such a low level that their continued exploitation is no longer sustainable
If this overexploitation is stopped in time species may recover but if not it can lead to extinction

3. It is estimated that around 70% of the world’s marine fishing grounds have been fully exploited and that many fish populations are reduced by 60-95%. This has resulted in lower catches of fish. In recent years efforts have been made to promote the recovery of fish stocks and give their populations a chance to recover. Some signs of recovery have been noted with a rise in numbers of some species.

4. Overexploitation of species can lead to a decline in genetic variation and complete loss of alleles within a population
This may limit the population’s ability to survive environmental changes

5. Habitat Fragmentation
Habitats can be split up into smaller areas called fragments
The total area provided by the fragments is less than that of the original habitat
Degradation of the edges of the fragments results in further decrease in size of habitats
Habitat fragments normally contain limited resources and are able to support a lower species richness

6. Habitat fragmentation can occur when a road is built through a habitat, the formation of a new river or canal, or the clearing of lands for human use.

7. Habitat Corridors
To try and overcome the issues of habitat fragmentation habitat corridors have been developed

8. Habitat Corridors
Habitat Corridors act as a link between two habitat fragments
This provides populations the opportunity to feed, mate and recolonise after local extinctions

9. Introduced, naturalised and invasive Species
When a foreign species is introduced (intentionally or accidentally) it may create a problem for native species
The new species may prey upon or outcompete the native species and cause a reduction in the native species numbers

11. Climate Change
The possible impact of climate change on biodiversity is based on data from computer models of climate change.
A programme might be set the task of forecasting changes to the richness of species would occur if these species:
Could manage to shift their range at the same pace as projected climatic shift or
Could only manage to shift to a few new areas owing to migration limitation