Maintaining Biodiversity (OCR Gateway GCSE Biology: Combined Science)

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Local & Global Biodiversity

Maintaining biodiversity

  • Biodiversity has advantages for both humans and other organisms, such as
    • Maintaining the human food supply
    • Keeping food chains and food webs intact
    • Providing materials for human needs e.g. wood for construction or medicines from plant extracts
  •  A drop in biodiversity is unsustainable over the long term as conditions change so it is in humans' best interests to promote biodiversity

Benefits and challenges of local biodiversity

  • Local biodiversity is the biodiversity in a small geographical area e.g. in a national park or within a single country
  • Governments can act to improve biodiversity within their country's borders, so laws can be passed to make biodiversity a legal requirement
  • Small, local schemes can form to protect areas of land or water
  • If enough of these form, they can join up and create 'corridors' of biodiversity that can act as an example of sustainable living to other areas
  • Ecotourism can be promoted to attract people to beautiful and wild landscapes
    • Whilst recognising that too much ecotourism would itself have a negative impact on biodiversity
    • Examples of ecotourism are whale-watching trips and tours around biodiversity-friendly farming schemes
  • Objections can be made because biodiversity projects require land that could be used for growing food or housing people
  • Local residents may have their incomes reduced eg. by a ban on fishing or hunting

Benefits and challenges of global biodiversity

  • Animals and plants do not respect country boundaries and many move between ecosystems throughout the world
    • e.g. migratory birds, fish and sea mammals like whales
  • Removing a species entirely from a food chain can collapse the whole food chain
    • Whether that's a producer (plant), a mid-level consumer or a top predator
  • So a global approach is required to benefit species other than humans
  • Governments need to co-operate with common goals however inter-country conflicts mean that such co-operation stops
  • Certain countries have cultural reasons to keep hunting certain species
    • e.g. Japan and commercial whaling - whale meat is a prized delicacy in Japan
    • Those countries fail to agree on global whaling restrictions, which are not legally-binding in any case
    • Or disguise their hunting as 'scientific' or 'research' whaling

Fish farming as a sustainable practice

  • By intensifying food production into certain areas like fish farming, biodiversity can be promoted by relying less on wild populations of fish like salmon
  • Ocean fishing can be very damaging to biodiversity, especially techniques such as trawling and the use of gillnets

Sustainable fishing 1Sustainable fishing 2

Measures to make commercial fishing more sustainable

Benefits of fish farming

  • Most fish are still caught in the wild (i.e. in the open ocean or in freshwater rivers and lakes)
  • However, overfishing has led to dramatic declines in many fish populations
  • Fish farms are ways of raising large numbers of fish in a small space to provide food (protein) for humans
  • Fish are bred in large tanks or cages to minimise energy losses and maximise yield

Methods to maximise yield in fish farms

  • Within fish farms, large numbers of fish are kept in freshwater or seawater enclosures and are carefully monitored and controlled in different ways (many of which are not possible with wild-caught fish)
    • Selective breeding ensures high quality, fast-growing fish
    • Interspecific predation is prevented using nets and cages
    • Intraspecific predation is limited by grouping fish according to their age and size
    • Water quality is carefully controlled by monitoring pH and temperature as well as removing fish waste or dead fish
    • Diet is controlled by feeding high protein fish pellets regularly to ensure rapid growth
    • Diseases and pests are prevented using antibiotics and pesticides or biological controls

The effect of fish farms on biodiversity

  • Fish farms, whilst reducing the pressure of overfishing of wild fish, can have a negative impact on biodiversity in several ways
    • Predators may be attracted to the fish farms and may get caught in nets trying to reach the fish
    • Diseases can spread quickly in fish farms due to the enclosed space and number of individuals in close proximity.
      • Diseases can also spread in the water to other species outside of the fish farm
    • If any caged fish were to escape, they can cause issues with the native species nearby (i.e. those that live in the area naturally)
    • Eutrophication can occur

Fish Farming Methods Table

Fish farming methods, downloadable IGCSE & GCSE Biology revision notes

The process of eutrophication

Non-Indigenous Species

  • An indigenous species is one which is native to a particular area
  • Introducing a non-indigenous species into an area can have negative effects on the native species
  • Introduction may be purposeful (for example, as a biological control) or it might be accidental (for example, if an organism escapes captivity)
  • Negative effects occur due to competition, impacts on the food chain and disease
  • This results in a decrease in the biodiversity of the habitat


  • The non-indigenous species may compete with native species for food, water or space
    • For example, the red squirrel is a native species of squirrel in the UK that has declined in numbers drastically due to the introduction of the North American grey squirrel
    • The grey squirrel not only carry the deadly parapox virus, which is fatal to red squirrels, but they also directly compete with red squirrels for food and nesting sites.
  •  This could result in one or more indigenous species being outcompeted and possibly being eradicated

Impacts on the food chain

  • A new species in the food chain would disrupt the balance as it would provide a new food source or a new predator
  • This would impact the populations of the other organisms in the food web
    • For example, the cane toad is a species of poisonous toad that was introduced into Australia as a biological control to help combat an infestation of beetles, which were destroying sugar cane
    • The toads then went on to infiltrate the local food webs, poisoning predators that ate them, which had a knock-on effect on other species in the food web
    • This led to the cane toad becoming a pest species in its own right


  • New species can bring with them new diseases which may be deadly to indigenous species
  • This can have minimal impact or it can be devastating for whole populations, either by total eradication or via long term effects on the health of the species
    • For example, Chalara Ash dieback (a fungus that grows on ash trees), which was brought over through imports of ash trees from Asia, is set to wipe out up to 80% of indigenous ash trees in the UK

Exam Tip

Biodiversity-promoting schemes can operate at a local level but also on a global scale; each type is valuable as humans try to tread the line between sustaining the growing population and maintaining biodiversity that benefits all species. 

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Phil has a BSc in Biochemistry from the University of Birmingham, followed by an MBA from Manchester Business School. He has 15 years of teaching and tutoring experience, teaching Biology in schools before becoming director of a growing tuition agency. He has also examined Biology for one of the leading UK exam boards. Phil has a particular passion for empowering students to overcome their fear of numbers in a scientific context.