Biodiversity and the Human Impact on Ecosystems

Biodiversity is a measure of the number of different species living in an area. Unfortunately, humans have had a drastic effect on biodiversity — and not in a good way. Through activities such as deforestation and overfishing, numerous species are threatened with extinction.

Biodiversity

Biodiversity is the variety of all the different species of organisms on earth, or within a particular ecosystem. The higher the biodiversity, the more stable an ecosystem is. This is because a species is not dependent on just one other species to survive. For example, if foxes are able to feed on both mice and rabbits, then they will be less affected if all the rabbits disappeared from the ecosystem, since they would have an alternative food source.

Maintaining biodiversity is important for a number of reasons:

• Many medicines are derived from plants and there may be plant species that have useful medicinal properties that we don’t know about yet

• Areas of natural beauty promote tourism, which creates jobs and brings money into an area

• We have an ethical responsibility to protect species for future generations

• Plant life plays an important role in keeping global temperatures stable by absorbing carbon dioxide. Cutting down trees on a large scale is having an impact on global warming, with devastating consequences for human and non-human life.

Many human activities have drastically reduced biodiversity on Earth. It is estimated that in the past fifty years, the population size of mammals, birds, reptiles and fish has reduced by almost 60%. Around one million plant and animal species are now threatened with extinction. It is only recently that measures to stop the reduction in biodiversity have been put in place.

Humans have contributed to the reduction of biodiversity in the following ways:

• Deforestation – to make room for houses, roads or to use the wood for furniture or fuel. Since plants provide food and habitats to other animals, we’re also reducing the diversity of animals able to survive there. Indonesia’s forests are disappearing incredibly fast, at a rate of one football pitch every 25 seconds, now only 10% of the Indonesian rainforest remains.

• Pollution – pollution from burning fossil fuels such as oil, coal and gas can remain in the air as particle pollutants or fall to the ground as acid rain. Acid rain, which is primarily composed of sulfuric and nitric acid, causes acidification of lakes, streams and sensitive forest soils, and can damage trees. In addition, chemical pollutants such as pesticides and herbicides leach into soils and watersheds. Some fish species, such as salmon, require small freshwater streams to spawn. Polluted streams result in the abandonment of traditional spawning areas and ultimately in the loss of salmon populations. Species’ sensitivity to pollution is variable. However, many species are vulnerable to the indirect effects of pollution through the concentration of toxic chemicals in top predators of food chains.

• Introduction of invasive species - an invasive species is one which is not native to a particular area and may have arrived in a new habitat accidentally (come on board a ship) or on purpose as a form of biological control. They may reproduce faster and be more likely to survive compared to the native species as they don’t have any natural predators in the area. They out-compete native species, resulting in a reduction in biodiversity. An example is the grey squirrel which has led to a reduction in the numbers of native red species in the UK.

• Hunting and poaching – the overexploitation (killing more members of a species than can be replaced naturally) has reduced biodiversity. For example, the black rhino is at risk of extinction due to the trade in rhino horn. Hunting is not the only form of overexploitation – overfishing is the biggest cause of declines in ocean wildlife populations. Unsustainable fishing methods have meant that fishing vessels catch fish faster than they can be replenished. Bycatch, the capture of unwanted sea life while fishing for a different species is also a serious marine threat which causes the needless loss of billions of fish, along with hundreds and thousands of sea turtles and crustaceans.

• Climate change – one of the consequences of climate change is extreme weather events, such as flooding due to melting sea ice. If a habitat becomes frequently flooded it may result in the migration of organisms from the habitat, reducing biodiversity in that area. Some species, such as plants, will not be able to move and may become extinct. An example of a species that has migrated as a result of climate change is the Sooty Copper butterfly which has moved 60 miles North due to increased temperatures. The movement of insects can have an effect on the prevalence of certain diseases in a habitat. For example, malaria-carrying mosquitos are moving to cooler regions and bringing malaria with them. Leishmaniasis, a deadly disease caused by a parasite which is carried by sandflies, is now affecting people in Northern Texas as the sandflies migrate north.

Waste management

The human population is growing exponentially. Every year, approximately 75 million more people are born than die. This rapid growth in the human population, along with an increased standard of living, means that more resources are being used and more waste is produced. Unless waste and chemical materials are properly dealt with, the world will become increasingly polluted. There are various forms of pollution:

• Water pollution – sewage and fertilisers which run into rivers and lakes can increase the growth of algae on its surface, leading to eutrophication. Sometimes factories produce toxic chemicals and dump these directly into nearby rivers and streams.

• Air pollution – the combustion of fossil fuels releases carbon dioxide, sulfur dioxide and nitrogen oxides. Carbon dioxide is a greenhouse gas and contributes to global warming. Sulfur and nitrogen oxides contribute to acid rain.

• Land pollution – when materials are not recycled they go into landfill, persisting in the environment for a very long time.

Water, air and land pollution can make it difficult for organisms to survive and result in a reduction in biodiversity.

Land use

Humans have reduced the amount of land available for other animals and plants, leading to a reduction in biodiversity, in the following ways:

• Clearing land for housing – as the human population grows, more land has been cleared to make space for housing. Extensive land clearing to make room to build houses is a particular problem in countries such as Australia and New Zealand.

• Clearing land for farming – huge areas of rainforest have been removed to make space for agriculture. By replacing forests with farms, we’re replacing an area of high biodiversity with an area of very low biodiversity. Often just one type of plant (e.g. palm oil trees) are grown – this is called a monoculture. Palm oil is used in many everyday products, such as processed foods and cosmetics. Deforestation to make room for palm oil trees has reduced the numbers of 193 threatened species, including orangutans, pigmy elephants and rhinos.

• Quarrying – quarrying is the process of extracting minerals from the ground. Quarrying involves the formation of a large pit in the ground and therefore destroys habitats and the species that live there.

• Landfill / dumping waste – areas are cleared to make space for landfill, which contributes to habitat loss and a reduction of biodiversity.

Peat bogs are a type of wetland which accumulates peat (deposits of dead plant material). They are acidic and often have very low levels of nutrients inside them. Because few decomposers (e.g. bacteria, fungi) are able to survive in these conditions, decomposition occurs very slowly, resulting in the formation of peat from partially decayed plants. Peat has been removed from peat bogs to be used for fuel or as compost. However, peat takes such a long time to form that it is classed as a non-renewable resource. The destruction of peat bogs reduces the area of the habitat and the diversity or organisms living there.

Peat bogs are also carbon sinks because they are very good at absorbing and storing carbon. Burning peat as a fuel or allowing it to decompose in the soil releases carbon dioxide into the atmosphere. If we keep removing peat from peat bogs, this would increase the amount of carbon dioxide in the atmosphere, contributing to the greenhouse effect.

Deforestation

Deforestation on a huge scale has taken place in tropical areas in order to:

1. Provide land for cattle and rice fields – a growing human population and an increased demand for beef has resulted in huge swathes of rainforest being removed to make room for cattle farming. Large areas of land have also been cleared to grow crops, such as rice and wheat. In the past 75 years, over 50% of the world’s rainforest have been removed, which is the equivalent to approximately 32,000 hectares every day. Most of the rainforest that has been removed (about 80%) is for cattle farming. Since cows produce methane, this further increases the amount of greenhouse gases in the atmosphere.

2. Grow crops for biofuels – deforestation has also occurred to grow crops to use as a sustainable fuel. Bioethanol and biodiesel are sustainable alternatives to petrol and are made from plant material. Since the production of biofuels requires a lot of plants, large areas of forest are often destroyed to make space to grow the crops.

Global warming

Greenhouse gases are gases which contribute to global warming. They include:

• Carbon dioxide - produced by burning fossil fuels

• Water vapour - formed from combustion reactions

• CFCs - product of aerosols and air conditioning units

• Methane - produced by cattle farming

• Nitrogen oxides - formed from burning fossil fuels, power stations and car exhaust fumes

Human activities have caused a significant increase in the levels of greenhouse gases in our atmosphere. Large scale deforestation to make room for housing and agriculture means less carbon dioxide is absorbed by trees for photosynthesis. Burning fossil fuels to generate electricity or to power cars also increases the level of carbon dioxide, nitrogen oxides and water vapour in the atmosphere.

When heat (infrared radiation) is emitted from the Sun towards the Earth’s surface, some is absorbed by the Earth and some is reflected back out towards space. Greenhouse gases in the atmosphere can trap some of this reflected infrared radiation, causing the Earth to become gradually warmer. A warming planet will cause the polar ice caps to melt, resulting in flooding and destruction of habitats which could have a destructive effect on many species and the rest of the food chain which depend on them. Global warming will also result in extreme weather events such as droughts, cyclones and hurricanes.

Maintaining biodiversity

We have seen how an increasing human population, improper waste disposal, peat bog destruction, global warming and deforestation have contributed to a decline in biodiversity. Conservation efforts have been put in place in an attempt to reduce the decline in biodiversity. Conservation involves protecting species from extinction, maintaining and restoring habitats and protecting biological diversity. Conservation work can be carried out in the following ways:

• Breeding programmes for endangered species

• Protection and regeneration of rare habitats

• Reintroduction of field margins and hedgerows in agricultural areas where farmers grow only one type of crop

• Reduction of deforestation and carbon dioxide emission by some governments

• Recycling resources rather than dumping waste in landfill