threats to biodiversity 8

• Over exploitation


  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
• Bottle neck effect


  Small populations may lose the genetic variation necessary to enable evolutionary responses to environmental change
• Loss of genetic diversity in small populations


  Can be critical for many species, inbreeding can result in poor reproductive rates
• Habitat fragmentation


  The clearing of habitats has led to this
• Degradation of habitat fragment edges


  Results in increased competition between species as the fragment becomes smaller
• Habitat fragmentation


  May result in a decrease in biodiversity
• Isolated habitat fragments


  Exhibit a lower species diversity
• Habitat corridors


  Allow movement of animals between fragments, increasing access to food and choice of mate, may lead to recolonization of small fragments after local extinctions
• Introduced species


  A species that humans have moved either intentionally or accidentally to new geographical locations
• Naturalised species


  Introduced species that have become established within the wild community
• Invasive species


  Naturalised species that spread rapidly and eliminate native species, therefore reducing species diversity
• Invasive species


  • Free from predators
  • Free from parasites
  • Free from pathogens (disease)
  • Free from competition that would have occurred in their own native habitat
• Invasive species


  May prey on native species, outcompete them for resources or hybridise with them
• Invasive species


  • Japanese Knot weed spreading throughout Great Britain
  • Grey squirrels outcompeting red squirrels throughout the UK