Human Impact on Ecosystems

The variety of different species in an ecosystem or on Earth.

Rearing fish in cages, tanks or ponds and feeding them until they are harvested.

A reliable supply of protein, and less overfishing of wild fish.

Pollution from waste and spread of parasites and disease to wild fish.

They compete with them and breed with them, which can reduce the wild population's genetic variation.

A species introduced to an area where it does not naturally live.

Deliberately (such as crops or pets) or accidentally (such as in cargo or ship ballast water).

It can outcompete, eat or spread disease to native species.

It may have no natural predators or diseases in its new home.

They compete for food and carry squirrelpox, which kills red squirrels.

Examples: crops such as potatoes feed people, or biological control reduces pests.

It is poisonous, so native animals that ate it died, and it did not control the beetle.

Excess mineral ions in water leading to an algal bloom, low oxygen and death of aquatic life.

Nitrates and phosphates.

The algae block the light, so they cannot photosynthesise.

Bacteria decompose the dead plants and algae and use up the oxygen in respiration.

There is not enough oxygen for them to respire.

Use less fertiliser, avoid spreading it before rain, or leave a vegetation strip beside the field.

Describe the sequence of events in the diagram, in order.

1 Fertiliser is washed off the field into the pond. 2 Algae grow fast and form an algal bloom. 3 The algae block the light, so the plants die. 4 Bacteria decompose the dead matter and use up the oxygen. 5 Fish and other animals die from lack of oxygen.

Name the parts of the fish farm and explain two harmful effects.

Net cage, fish feed, uneaten food and faeces, escaped farmed fish, wild fish. The waste pollutes the water and seabed (it can cause eutrophication). Parasites and disease spread to wild fish, and escaped farmed fish compete and breed with wild fish.

The variety of species in a small area such as a pond, hedgerow or woodland.

The variety of all the species on Earth.

There are many food chains, so if one species declines others can fill the gap.

All the different alleles in a population or species.

Any two of: food, medicines, materials, pollination, climate, jobs and tourism.

Aspirin from willow bark, quinine from cinchona bark, or a leukaemia drug from the rosy periwinkle.

They have alleles for traits such as disease resistance that can be bred into crops.

A single disease or pest can destroy the whole crop.

Protecting and managing species and habitats so that species do not die out.

Protected areas, laws against hunting and trade, and captive breeding.

Breeding endangered animals in zoos or centres and releasing young into the wild.

The population may have little genetic variation, or animals may not survive in the wild.

Planting trees on land that was cleared of forest.

Roots hold the soil and the trees take up water, so less runs off quickly into rivers.

Trees take in carbon dioxide for photosynthesis and store carbon.

It gives food and shelter to far fewer species than a mixed native forest.

The change divided by the original value, multiplied by 100.

The species is lost for ever, with any medicines, genes or ecosystem roles it had.

Describe the differences in biodiversity between the two panels, and explain why it matters.

The left is a crop monoculture with low biodiversity: one species, so a single disease or pest could destroy it, and few animals can live there. The right has high biodiversity: many species, more food sources and shelter, so it is more stable and better able to cope with change.

Explain how reforestation changes what happens to the rain.

Without trees, the rain runs off and washes the soil away (erosion) into the river, which becomes muddy and may flood. With trees, the roots hold the soil and the trees take up water, so the river stays clear. The trees also take in carbon dioxide and give animals a habitat.