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

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

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.

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

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

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.

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

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

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

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