Loss of Biodiversity (DP IB Biology)
Revision Note
Biodiversity Loss: Evidence
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.
Biodiversity Loss: Causes
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
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