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Impacts on biodiversity

Biodiversity is affected by many things:

Climate: The impact of changing climate is likely to have impacts on biodiversity. See the climate change page for more detail. Earthwatch is conducting research into the impact of climate change on biodiversity.
Fire, a natural component of many ecosystems, effects animal populations. Earthwatch is conducting research into the impact of fire on ecosystems in Australia
Natural disasters such as earthquakes and volcano eruptions.
Human activities are placing pressures on biodiversity and in many instances leading to losses in diversity.

Biodiversity fluctuation is natural. Ecosystems are dynamic and over time the numbers and densities of species will vary. Species will be lost and new species will evolve. This is natural change. However big fluctuations in biodiversity today are commonly accepted to be due to human use of resources and human activities. The impact of humans is dealt with in this section. For more information on the political and economic reasons for biodiversity loss visit WWF’s Macroeconomics for Sustainable Development Office website

Direct use of natural resources

Exploitation of Natural Resources has pushed some species to the verge of extinction.
• Exploitation of animals has left many species threatened, including the tiger, elephants and Black Rhinoceros.
• Marine stocks have been dramatically reduced as fishing methods improved and the quantities harvested from the sea increase.
• Many habitats are being lost due to deforestation in order to meet growing demands for wood as well as other materials found in forested areas.

Habitat loss and Fragmentation

For centuries, landscapes have been altered by humans through deforestation, fire and over-use. The result is often a simplification of habitats that has led to the local loss and ultimate extinction of species and an overall loss of biodiversity.

Habitat loss is identified as a main threat to 85% of all species described in IUCN Red Lists. Fragmentation of habitats can expose the interiors of remaining habitat to edge effect, which benefits some species but harms many others.

Small fragments of habitat can only support small populations of fauna and small populations of fauna are more vulnerable to extinction. Fragments of habitat that are separated from each other are unlikely to be recolonised. Also many birds and mammals need large areas in which to feed and breed.

The inside of a habitat has a different climate and supports different species to the edge. Small fragments of habitat do not contain this interior habitat. Habitat along the edge of a fragment has a different climate and favours different species to the interior. Small fragments are therefore unfavourable for those species which require interior habitat and may lead to the extinction of those species.
When native vegetation is cleared for agriculture, urban developments or roads, habitats which were once continuous become divided into separate fragments. After intensive clearing, the separate fragments tend to be very small islands isolated from each other by areas unsuitable for wildlife.

Deforestation is one of the leading causes of habitat and biodiversity loss. As tropical forests contain at least half of the Earth's species, the clearance of some 17 million hectares each year is causing a dramatic loss of biodiversity. As the world population exceeds six billion people, the pressure on land for building and agriculture, in particular, add to concerns for biodiversity conservation.


Oceans, rivers, lakes and lands have become repositories for society’s industrial and organic waste. Pollutants entering our environment travel through the food web increasing in concentration in the tissues of animals further up the food chain. This can reduce survival and lower reproductive success of many species. Amphibians, for example, are key indicators of ecosystem health. Scientists have found that commonly used chemicals such as pesticides, herbicides and fertilizers are decimating frog populations. The reduced abundance and diversity of frog species are a warning signal about the impacts of pollution.

Large volumes of pollution overwhelm the Earth’s capacities to absorb, transform or break down these materials. Some materials take thousands of years to decay, and may become more toxic as they decompose, resulting in long-term environmental damage.
Eutrophication is a major problem in many water systems where agricultural waste and fertilizers run off the land and into rivers and lakes. The increased nutrient content in the water causes excessive algal growth reducing the amount of light which enters the water leading to an increase in anaerobic bacteria activity and reduced oxygen content in the water. The lowered levels of oxygen make the water unlivable for many plants and animals.

Invasive species

An "alien" or "exotic" species is one that occurs in an area outside its historically known natural range as a result of either intentional or accidental dispersal by human activities. Sometimes, alien plants or animals become established in their new environment and spread unchecked, threatening native biodiversity. Invasive exotic species have been identified as the second greatest threat to biodiversity after habitat loss.

When a new species is introduced - accidentally or not - in an area, it can have major impacts on native species that have evolved no defences against such invaders. Natural barriers to the movement of certain plants and animals provide the isolation which resulted in unique species and ecosystems evolving. Island species are often the most vulnerable because they will have been isolated from other species for long periods of time and developed high levels of endemism.

The Convention on Biological Diversity includes an article specifically calling for the prevention, control, and eradication of alien species that threaten ecosystems, habitats, or species.

In the 1970’s the Louisiana Crayfish was introduced to Lake Naivasha in Kenya to provide a boost for the local fishermen. The crayfish produced good yields for the first few years after introduction but then started to severely affect the food chain in the lake. Research is being conducted into the impacts of the Crayfish on the lakes ecosystem by Earthwatch.

Visit the Invasive Species Specialist Group (ISSG) part of the World Conservation Union (IUCN) for more information on invasive species.


Photo credit: nile Crocodile eye, Leslie

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