Loss of Biodiversity (HL IB Biology)

The evidence for biodiversity loss

• To fully understand the nature and extent of the biodiversity crisis, solid evidence on the world's changing biodiversity is required
• For such evidence to be trustworthy, it needs to contain sufficient data and it needs to come from reliable sources:
  • Many reliable biodiversity surveys need to have been carried out in a wide range of habitats
  • Repeat survey data is needed over a period of time
  • Both species richness and species evenness need to be assessed
  • To maximise the volume of data, 'citizen scientists' can help with survey work
    • Citizen scientists are members of the public who help to gather data
  • Data need to be expertly analysed
• Drawing together these large bodies of evidence is a huge task, and such work is often carried out by organisations that work across multiple governments, e.g.
  • IPBES
    • Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services
  • IUCN
    • International Union for the Conservation of Nature

IPBES

• IPBES is an organisation that works to gather information, recommend policies, and communicate findings relating to global biodiversity and ecosystems
• The 2019 IPBES report contained a comprehensive summary of findings from research as well as policy recommendations for governments
  • Data is gathered by scientists, government bodies, and local individuals
  • Studies are carried out in a range of habitats where regular samples are taken

IUCN

• The IUCN is a network of organisations and individual experts that seeks to gather knowledge of the natural world and to propose helpful environmental policies
• The IUCN red list is a list of the world's most threatened species; it has assessed more than 150 000 species, and has listed more than 42 000 as threatened
• The IUCN red list has been compiled by scientists and scientific organisations all around the world, and is used by many groups to inform conservation efforts
• Species that have been assessed are categorised by the IUCN as:
  • LC = least concern
  • NT = near threatened
  • VU = vulnerable
  • EN = endangered
  • CR = critically endangered
  • EW = extinct in the wild
  • E = extinct
• Species can also be classed as DD (data deficient) when there is not enough data on which to base a category choice, or as NE (not evaluated)

The IUCN categorises species on the basis of their risk of extinction; this data can be represented visually to give an immediate picture of the level of risk being faced by many species

Note that this graphic is from 2016, so does not match the numbers given in the text above

NOS: To be verifiable, evidence usually has to come from a published source, which has been peer-reviewed and allows methodology to be checked

• Collecting data on global biodiversity is a huge task, and while qualified scientists can collect a great deal of data, this may not be enough to gain an overall picture of changes occurring at a national or international level
• To solve this problem, organisations will sometimes ask the public to help with data collection; such members of the public are described as 'citizen scientists'
• Citizen scientists are often untrained, and may not always collect valid data as a result, so there will be a certain amount of trade-off between the quality and the quantity of the data
• Good experimental design and high-quality data analysis can help to mitigate the effects of using citizen scientists.

The causes of biodiversity loss

• It is widely agreed among scientists that there is a biodiversity crisis underway due to the rate at which extinctions are occurring
• The growth of the global human population is likely to be the main cause of this crisis
  • There are currently more than 8 billion people on Earth
  • The global population continues to increase
  • Even though birth rates are now decreasing, people are living longer so births are occurring at a higher rate than deaths and the population continues to grow

Human population graph

Projections suggest that the human population will continue to increase until the year 2100 due to birth rates being higher than death rates

Note that the graph shows population size in red, projected population size in orange, and population growth rate in blue.

• Human population growth has led to a biodiversity crisis for multiple reasons, e.g.
  • Overexploitation of resources
    • Overfishing of the oceans are causing a decline in fish populations
    • Hunting of animals for resources such as ivory from tusks, oil from whales, or fur from beavers
  • Urbanisation, or the building of towns
    • Direct loss of habitat for buildings
    • Fragmentation of habitat into smaller pieces by, e.g. roads
    • Less land is available for agriculture, so this expands elsewhere
  • Deforestation and habitat loss
    • Land is cleared for agriculture, timber, mining, or quarries
    • Agriculture may look good for living organisms, but it often involves the planting of monocultures with very low biodiversity, and it leads to loss of soil micro-organisms
  • Pollution
    • Microplastics have been found in remote environments
    • Fertilisers and organic waste can be washed off farmland into bodies of water
  • Increase in numbers of pests
    • Biodiversity loss has led to an increase in pest species that damage crops, e.g. the cotton bollworm (Helicoverpa armigera)
      • Higher biodiversity increases the number of pest predators
      • Pests will gather in larger numbers in areas of monoculture
  • Invasive species
    • When humans travel around the world they often bring species with them, either by accident or on purpose; these 'alien' species can have damaging effects on the habitats to which they are introduced
    • Examples include
      • Grey squirrels and signal crayfish in the UK
      • Cane toads in Australia
      • Rats in the Galapagos Islands
  • Disease
    • Diseases can wipe out large numbers of species, e.g. the chytrid fungus is thought to have wiped out 90 species of amphibian so far
    • Human-caused climate change can increase the ranges of some diseases
    • Humans living closely with animal species can result in new diseases as pathogens transfer between hosts