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Biology · Human Impact on Ecosystems

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Biology · Edexcel Paper 2

Human Impact on Ecosystems

Fish Farming, Introduced Species and Eutrophication

Every way in which people use ecosystems has benefits and costs, and biodiversity is what is lost when the costs are ignored.

  • Biodiversity The variety of different species of organisms in an ecosystem or on the whole Earth.
  • Fish farming Rearing fish in cages, tanks or ponds, feeding them and harvesting them for food.
  • Non-indigenous species A species that has been introduced to an area where it does not naturally live.
A net cage of farmed fish in the sea, with feed going in, waste falling to the seabed, a fish escaping, and parasites spreading to a wild fish.
Fish farms bring food and jobs, but can pollute the water and harm wild fish.

Fish farming: benefits and problems

  • Benefits A reliable supply of protein for people; Less overfishing of wild fish, so wild stocks can recover; Jobs and income for coastal communities
  • Problems Waste and uneaten food pollute the water and can cause eutrophication; Parasites and disease spread to wild fish; Escaped fish compete and breed with wild fish

The sequence of events in eutrophication

  • Fertiliser enters the water Rain washes nitrates and phosphates from fertilised fields.
  • Algal bloom With plenty of mineral ions, the algae grow and reproduce very quickly.
  • Light is blocked The algal bloom stops light from reaching the plants below.
  • Bacteria use up the oxygen Bacteria decompose the dead algae and plants.

The Benefits of Maintaining Biodiversity

Keeping biodiversity high keeps ecosystems stable and gives people food, medicines, materials and a healthy climate.

  • Conservation Protecting and managing species and their habitats so that they do not become extinct.
  • Extinction The permanent loss of a species, when the last individual has died.
  • Gene pool All the different alleles of all the genes in a population or species.
A field of one crop beside a meadow with many different plants and animals, showing low and high biodiversity.
A field of a single crop supports few other species. A habitat with many species supports many more.

A crop monoculture or a mixed habitat?

  • Low biodiversity (one crop) Few species of plants and animals; A single disease or pest can destroy it; Little food and shelter for wildlife
  • High biodiversity (mixed habitat) Many species of plants and animals; A disease or pest only affects some of the species; Plenty of food and shelter for wildlife