Biodiversity and human impact

Biodiversity is the variety of all the different species of organisms on Earth, or within an ecosystem. A rich variety makes ecosystems more stable, because species depend less on any one other species. As the human population grows, we use more land and resources and make more waste, and biodiversity falls. We can also act to protect it.

Key facts

  • High biodiversity makes an ecosystem more stable: species depend less on any one other species for food, shelter and the conditions they need.
  • Pollution can happen in water (sewage, fertiliser and toxic chemicals), in the air (smoke and acidic gases that cause acid rain) and on land (landfill and toxic chemicals). Pollution kills plants and animals and reduces biodiversity.
  • Humans take land from other species for building, quarrying, farming and dumping waste. Draining peat bogs for compost destroys habitats and releases carbon dioxide.
  • Large-scale deforestation in the tropics, for cattle, rice fields and biofuel crops, reduces biodiversity and adds carbon dioxide to the air: less is taken in by photosynthesis, and burning and decay release more.
  • Carbon dioxide and methane in the atmosphere cause global warming. Its effects include loss of habitats, changes in where species live, changes in migration and a fall in biodiversity.
  • Biodiversity can be protected by breeding programmes for endangered species, protecting and regenerating rare habitats, replanting hedgerows and field margins, reducing deforestation and carbon dioxide emissions, and recycling instead of using landfill.
  • At A-level, diversity can be measured with an index of diversity: d = N(N − 1) ÷ Σn(n − 1), where N is the total number of organisms and n the number of each species.

Worked examples

Example 1

Explain how fertiliser running into a lake can kill the fish.

  1. The fertiliser adds nitrates and phosphates, so algae grow quickly on the surface.
  2. The algae block the light, so plants under the water die.
  3. Decomposers break down the dead plants and use up the oxygen in the water as they respire.
  4. The fish die from lack of oxygen.

Answer: algae grow and block the light; plants die; decomposers break them down and use up the oxygen; fish die

Example 2

A forest covered 800 km² in 2000 and 560 km² in 2020. What is the percentage change in its area?

  1. Find the change. 560 − 800 = −240 km²
  2. Divide by the original area and multiply by 100. −240 ÷ 800 × 100 = −30%
  3. The minus sign shows a decrease of 30%.

Answer: −30%

Example 3

A meadow has three species with 10, 8 and 2 individuals. Calculate the index of diversity.

  1. Add up all the organisms. N = 10 + 8 + 2 = 20
  2. Work out n(n − 1) for each species and add. 10 × 9 + 8 × 7 + 2 × 1 = 148
  3. Put the numbers into the formula. d = 20 × 19 ÷ 148 = 2.57

Answer: 2.57