The variety of life

• Biodiversity

  The study of all the variation that exists within and between all forms of life, as well as the variation of genes
• Levels of biodiversity assessment


  • The number and range of different ecosystems and habitats
  • The number of species and their relative abundance
  • The genetic variation within each species
• Biodiversity is very important for the resilience of ecosystems; in that it allows them to resist changes in the environment
• Ecosystem or habitat diversity


  The range of different ecosystems or habitats within a particular area or region
• High number of different habitats within an area


  Area is likely to have high biodiversity
• Low number of different habitats within an area


  Area is likely to have low biodiversity
• Species diversity


  Includes the number of different species in an ecosystem, and also the abundance across the different species present
• Ecosystems with high species diversity are usually more stable than those with lower species diversity as they are more resilient to environmental changes
• Genetic diversity


  The diversity of alleles and genes in the genome of species
• Genetic diversity is measured by working out the proportion of genes that have more than one form (allele) and how many possible alleles each gene has
• Genetic differences or diversity between populations of the same species

  May arise because the two populations occupy slightly different ranges in their habitat and so are subject to slightly different selection pressures that affect the allele frequencies in their populations
• Genetic diversity in a species is important as it can help the population adapt to, and survive, changes in the environment
• Genetic diversity is limited in populations that are very small or isolated
• Inbreeding in small, isolated populations leads to a high proportion of individuals being homozygous (e.g. AA to aa) for many genes, resulting in lower genetic diversity
• Endemism


  Certain species only occur in one particular area of the world
• Endemic species are particularly at risk of extinction due to their limited range
• As the human population increases and countries become more economically developed, our requirement for natural resources also increases
• This is having a harmful effect on many aspects of the environment, including aquatic and terrestrial ecosystems, and our atmosphere and climate
• Main factors affecting biodiversity today

  • Habitat destruction
  • Overexploitation
  • Hunting
  • Agriculture
  • Climate change
• Habitat destruction


  When land is cleared for agriculture, industry, energy production housing, transport, leisure facilities, waste disposal and water storage, this results in habitat loss and habitat fragmentation
• Deforestation is one of the most damaging forms of habitat destruction, as forest habitats often have the highest levels of biodiversity
• Marine habitats are also being destroyed, including coral reefs and sea beds
• Hunting


  Many wild, non-farmed species of animals are being hunted and removed more quickly than their wild populations can be replenished
• Agriculture


  Modern farming practices have had a major negative impact on the level of biodiversity present in farmed areas
• Modern farming practices


  • Farms became more specialised so they grew only one crop or raised one type of livestock (monoculture)
  • Switch to growing cereal crops rather than vegetables
  • Fields were made bigger to accommodate machinery via the removal of hedgerows and stonewalls
  • More land was made arable by draining wetland and filling in ponds
  • The use of fertilisers and pesticides massively increased
• Monocultures support much lower levels of biodiversity compared to natural habitats or even natural grazing land
• Hedgerows represent an important habitat for many insects, small mammals and birds, which can nest there. As hedgerows are being increasingly removed, this habitat and the biodiversity it supports is lost
• Fertilisers can leach into waterways, causing eutrophication, which can lead to the death of many aquatic invertebrate and fish species
• Pesticides (e.g. insecticides) used on crops kill insect pests but also kill many non-target species, including important insect pollinators like bees
• Climate change


  Human-caused climate change is causing weather patterns to change and the frequency of extreme weather events, such as hurricanes, typhoons, floods and droughts, to increase
• It is feared that climate change is now occurring too fast for many species to be able to adapt to these changes, which could result in many species becoming extinct and a major decline in biodiversity
• Global warming (a result of climate change)


  Causing many species to move towards the poles or to higher altitudes, which may lead to them out-competing or being out-competed by the species already present in these habitats, resulting in decreased biodiversity
• Some species (such as plant species) may not be able to move or change their distributions fast enough to adapt to increasing temperature and may go extinct as a result
• Increasing atmospheric CO₂ is leading to more CO₂ dissolving in seawater, decreasing its pH (known as ocean acidification). This is negatively affecting organisms that require calcium carbonate for shells (e.g. plankton and coral polyps)
• Increased ocean temperatures have also led to an increased frequency of coral-bleaching events, where the tiny organisms that live inside corals and help keep them alive leave due to temperature stress. Without these organisms, the corals die and are broken down, eventually leading to the loss of whole coral reefs and as a result, the loss of the huge amount of biodiversity that depends on them