(a) Exploitation and recovery of populations and the impact on their genetic diversity.

• With overexploitation, populations can be reduced to a low level but may still recover. 

• Some species have a naturally low genetic diversity in their population and yet remain viable.

• The bottleneck effect — small populations may lose the genetic variation necessary to enable evolutionary responses to environmental change.

  • In small populations, this loss of genetic diversity can be critical for many species, as inbreeding can result in poor reproductive rates.

(b) Habitat loss, habitat fragments and their impact on species richness.

• The clearing of habitats has led to habitat fragmentation. 

  • More isolated fragments and smaller fragments exhibit a lower species diversity.

• Degradation of the edges of habitat fragments results in increased competition between species as the fragment becomes smaller. 

• This may result in a decrease in biodiversity.

• To remedy widespread habitat fragmentation, isolated fragments can be linked with habitat corridors.

  • The corridors allow movement of animals between fragments, increasing access to food and choice of mate. 

  • This may lead to recolonisation of small fragments after local extinctions.

(c) Introduced, naturalised and invasive species and their impact on native populations.

• Introduced (non-native) species are those that humans have moved either intentionally or accidentally to new geographic locations.

• Those that become established within wild communities are termed naturalised species.

• Invasive species are naturalised species that spread rapidly and eliminate native species, therefore reducing species diversity. 

• Invasive species may well be free of the predators, parasites, pathogens and competitors that limit their population in their native habitat. 

• Invasive species may prey on native species, out-compete them for resources or hybridise with them.