Human Impact on the Environment (OCR A Level Biology): Revision Note

Human Impact on the Environment

• There has been rapid human population growth on Earth since the 18th century

• Humans need food, space for infrastructure and farming, clean water and resources

• The increasing need for resources means that humans are having a disproportionate effect on other species

• Effects of human activities that are influencing animal and plant populations include:

  • climate change

  • introduction of non-native species

  • hunting by humans

  • degradation and loss of habitats

Human activities affecting plant and animal populations

Burning fossil fuels

• The large-scale burning of fossil fuels by humans in recent years has led to a large increase in the levels of carbon dioxide in the atmosphere

• The increased carbon dioxide concentration in the atmosphere has resulted in higher average global temperatures, the effects of which include:

  • changes in weather patterns

  • melting polar ice caps

  • rising sea levels, causing flooding and salination of soil in coastal areas

  • rising ocean temperatures and acidity

• These effects have changed the habitats of some species, putting their survival at risk

  • E.g. polar bears are struggling to survive as more of their habitat melts away earlier each year; the earlier melting of the ice caps means they have to swim further to reach seal populations that they prey upon for food

Introduction of species

• The introduction of non-native species can occur due to, e.g.:

  • travel, e.g. marine species in the ballast water of ships

  • keeping animals as pets, e.g. cats introduced to Australia

  • growing attractive plants in gardens, e.g. Rhododendron ponticum in the UK

  • the introduction of biological pest control, e.g. cane toads in Australia

• Non-native species can be highly problematic as they often have no natural competitors, predators or pathogens that help limit population growth

• Without natural population control, populations of non-native species can grow very quickly 

• Non-native species can negatively affect native species through factors such as competition and disease

Hunting

• Hunting animals for food can result in overexploitation of a natural resource; if populations are hunted so much that they are unable to recover then extinction may result, e.g.

  • passenger pigeon

  • dodo

  • Pyrenean ibex

• Harvesting animals for food must be carried out in a sustainable way to ensure that extinctions do not occur, e.g. by implementing sustainable fishing practices

Habitat loss

• Humans cut down forests and drain wetlands to create land for farming, as well as polluting water, soil and air

• As their habitat area is reduced a species will:

  • search for other suitable habitats

  • compete for the remaining habitat

• Eventually the range of habitat can become so small that a species is not able to survive and becomes extinct

Controlling the effects of human activities

• There are many control measures in place across the globe to help mitigate the impact of human activities on plant and animal species; these measures will vary depending on the country and on the impacts that need to be addressed

• Examples include:

  • prohibiting import and export of species

  • putting restrictions in place to control the impact of humans on animal and plant populations, e.g.

    • Certain areas cannot be used for agriculture, housing and infrastructure

    • Policies are in place to ensure environmental tests are carried out before building on undeveloped land

  • reducing sources of greenhouse gases, for example the burning of fossil fuels for electricity, heat, or transport

  • increasing the capacity of “sinks” that store greenhouse gases, such as the oceans, forests, and soil