Human Interactions and Biodiversity

Building on land, draining wetlands, quarrying and ploughing for crops destroy the habitats of the wild species that lived there. The species may die out, or move away and become more crowded elsewhere.

Hedgerows removed to make big fields, a single crop grown over a huge area (a monoculture) and the use of pesticides leave less food and shelter for wild plants and animals.

The clearing of forest, for timber and to make space for farms, plantations and roads. Tropical rainforests cover a small part of the land but hold more than half of all species, so their loss is a huge loss of biodiversity.

Fewer trees take in less carbon dioxide, and burning the wood adds carbon dioxide, which contributes to climate change. Without roots the soil can be washed away, and rainfall patterns can change.

The passenger pigeon was one of the commonest birds in North America, but it was hunted in huge numbers, and the last one died in 1914. Rhinoceroses and elephants are killed illegally for their horn and tusks.

Fish are caught faster than they can breed. The cod fishery off Newfoundland collapsed in the early 1990s, after decades of overfishing, and has still not fully recovered.

Rare plants, such as orchids, and animals for the pet trade are collected from the wild.

The loss of one species can harm others that eat it, or that it eats, because of interdependence.

Fertiliser washed from fields and sewage cause eutrophication. Oil spills coat birds and mammals, and plastic is swallowed by marine animals.

Burning fossil fuels releases sulfur dioxide, which dissolves in rain to make acid rain, and which kills lichens and damages trees and the life in lakes.

Pesticides and other poisons build up along food chains. In the 1950s the insecticide DDT made the eggshells of birds of prey so thin that they broke, and the numbers of peregrine falcons fell sharply.

Some organisms are sensitive to pollution, and their presence or absence shows how polluted a place is. Lichens are sensitive to sulfur dioxide in the air.

Rats, cats and stoats brought to islands by ships eat the eggs and young of birds that evolved without predators. The dodo on Mauritius became extinct this way.

The grey squirrel, brought from North America to Britain in the 1800s, eats more of the food and lives at higher densities than the red squirrel, which has declined.

The grey squirrel also carries the squirrelpox virus, which kills red squirrels but not greys.

Himalayan balsam spreads along rivers and crowds out native plants, and the Nile perch put in Lake Victoria in the 1950s has driven many of the native fish to extinction.

National parks, nature reserves and marine protected areas are legally protected from building, hunting and fishing, so that species can live there safely.

Rare animals are bred in zoos and safari parks and released back to the wild. The Arabian oryx was extinct in the wild by 1972, but it has been reintroduced to Oman and nearby countries.

Wetlands are restored, hedgerows and woodlands are planted, and meadows are managed for wildflowers. Wildlife corridors link fragments of habitat.

Laws limit hunting, fishing quotas protect fish stocks, the trade in endangered species is banned by an international agreement called CITES, and laws such as the Clean Air Acts cut pollution.

Forests are replanted after being logged, and fish are caught with nets of a large mesh size so that the young escape. The resource is used without using it up.