SI8- threats to biodiversity

• With overexploitation, populations can be reduced to a low level but may still recover if overexploitation is stopped soon enough
• If this does not happen they will become extinct
• The bottleneck effect occurs when environmental disaster or human overexploitation drastically reduces a population's size and genetic diversity
• A small population 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
• Some species have a naturally low genetic diversity in their population and yet remain viable
• The clearing of habitats has lead to habitat fragmentation
• 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
• More isolated fragments and smaller fragments exhibit a lower species diversity
• 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
• Habitat corridors increase genetic diversity
• This may lead to re-colonisation of small fragments after local extinctions
• 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 as 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 natural habitat
• Invasive species may prey on native species, outcompete them for resources or hybridise with them