Biosphere integrity at Higher Level: The same boundary as SL, with different evidence: Germany's vanishing insects, Latin America's wildlife, and both of the measures scientists use for this boundary.
Practise this as you read
- Name both parts: genetic and functional diversity.
- Quote each measured value against its boundary.
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One boundary, looked at closely: The planetary boundaries model shows that biosphere integrity has passed a critical threshold. It is one of the boundaries furthest beyond its safe limit.
The points to remember
- Biosphere integrity is the health of the living world: all its species and ecosystems.
- It has two parts: genetic diversity (the variety of genes and species) and functional diversity (the jobs species do).
- Ecosystems and species depend on each other: ecosystems support species, and species keep ecosystems working.
- So when an ecosystem is disturbed, species are lost; and when species are lost, the ecosystem works less well.
Remember it as: Species hold up ecosystems; ecosystems hold up species.
Real example: in nature reserves in Germany, the weight of flying insects caught in traps fell by 76% over 27 years (1989-2016). Fewer insects means less pollination, less food for birds and slower decomposition.
Genetic diversity
- The variety of genes and species
- Measured by the extinction rate
- Lost when species die out
Functional diversity
- The jobs species do
- Pollinating, decomposing, grazing
- Lost when those jobs stop
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Human activity has disturbed ecosystems on every continent and in every ocean, and this is what has worn down biosphere integrity.
How human activity erodes it
- Habitat loss: forests, wetlands and grasslands turned into farms, cities and roads (the biggest cause).
- Overexploitation: overfishing, hunting and logging faster than species can recover.
- Climate change: species cannot move or adapt fast enough.
- Pollution: pesticides, fertiliser and plastics.
- Invasive species: rats, cats and other species brought in by people.
Remember it as: Habitat, harvest, heat, poison, invaders.
Real example: in Latin America and the Caribbean, monitored wildlife fell by 95% on average between 1970 and 2020, mainly as forests and grasslands were cleared for cattle and crops.
An average fall, not a count: A 73% fall means monitored populations are, on average, about a quarter of their 1970 size. It does not mean 73% of all animals, or 73% of species, have gone.
How do we know the boundary has been crossed? The clearest evidence is the extinction rate.
The points to remember
- Before humans, about 1 extinction per million species per year (the background rate).
- The planetary boundary is 10 extinctions per million species per year.
- Today's rate is over 100: more than ten times the boundary.
- So the boundary for biosphere integrity has been crossed, and it is in the high-risk zone.
Remember it as: Background 1, boundary 10, today over 100.
Functional diversity is measured by how much of the plants' yearly growth humans take for food, timber and fuel. The boundary is 10%; humans now take about 30%, so less is left to feed the rest of life.
Real example: a 2023 update of the model by Richardson and colleagues judged both parts of biosphere integrity to be well beyond their boundaries, in the high-risk zone.
A rate, not a total: Quote the extinction rate with its unit, 'per million species per year', and compare it with the boundary of 10.
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How this comes up: Paper 2, Section A: a table of boundary data; explain why a boundary is judged crossed [3].
Figure 1 shows the boundary and the value reported in 2023 for the two parts of biosphere integrity.
Explain why the planetary boundary for biosphere integrity is judged to have been crossed.
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