factors affecting biodiversity Flashcards
intro
Maintaining biodiversity is essential for preserving a balanced ecosystem for all organisms. As species are interconnected within an ecosystem, the removal of one species can have a profound effect on others. For example, it could lead to a loss of another species’ food source or shelter.
As part of the human population you rely on biodiversity for many of the materials you need to survive, such as food, wood, and oxygen.
However, humans are the leading cause of loss of biodiversity.
human influence on biodiversity
The human population is growing at a dramatic rate. There are now over seven billion people living in the world, over double the number alive in the 1960s and over seven times more than in 1800.
This increasing growth rate is linked to improvements in medicine, hygiene, housing, and infrastructure, which enable people to live for longer.
To create enough space for housing, industry, and farming to support the increasing population, humans are severely disrupting the ecology of many areas. The main problems are occurring as a result of:
• deforestation - the permanent removal of large areas of forest to provide wood for building and fuel (known as logging), and to create space for roads, building and agriculture.
-agriculture - an increasing amount of land has to be farmed in order to feed the growing population. This has resulted in large amounts of land being cleared and in many cases planted with a single crop (monoculture).
• climate change - there is much evidence that the release of carbon dioxide and other pollutants into the atmosphere from the burning of fossil fuels is increasing global temperatures.
Other forms of pollution result from industry and agriculture, such as the chemical pollution of waterways. The improper disposal of waste and packaging is a form of environmental pollution called littering.
deforestation
Deforestation can occur naturally, for example as a result of forest fires caused by lightning or extreme heat and dry weather. However, most deforestation now occurs deliberately as a result of human action.
Some areas of forest have also been destroyed indirectly by humans through acid rain, which forms as a result of pollutants being released into the atmosphere.
Deforestation affects biodiversity in a number of ways. For example:
• It directly reduces the number of trees present in an area.
• If only a specific type of tree is felled, the species diversity is reduced. For example, rosewood is often extracted from rainforests (it is used in the manufacture of furniture and guitars), but less useable trees may be left intact.
• It reduces the number of animal species present in an area as it destroys their habitat, including their food source and home. This in turn reduces the number of other animal species that are present, by reducing or removing their food source.
• Animals are forced to migrate to other areas to ensure their survival.
This may result in the biodiversity of neighbouring areas increasing.
In some areas forests are now being replaced. Although this helps to restore biodiversity, generally only a few commercially viable tree species are planted. Therefore, biodiversity is still significantly reduced from its original level.
agriculture
In general, farmers will only grow a few different species of crop plants, or rear just a few species of animals. Farmers often select the species based on characteristics that give a high yield (high levels of production), for example, wheat that produces the most grain or dairy cows that produce the most milk. The selection of only a few species greatly reduces the biodiversity of the area.
In order to be economically viable, once the farmers have selected their desired species, a number of techniques are used to produce as many of the desired species as possible, maximising food production.
Unfortunately many of these techniques lead to a reduction in biodiversity, for example:
• Deforestation - to increase the area of land available for growing crops or rearing animals.
• Removal of hedgerows - as a result of mechanisation, farmers remove hedgerows to enable them to use large machinery to help them plant, fertilise, and harvest crops. It also frees up extra land for crop growing. This reduces the number of plant species present in an area and destroys the habitat of animals such as blackbirds, hedgehogs, mice and many invertebrates.
• Use of chemicals such as pesticides and herbicides. Pesticides are used to kill pests that would eat the crops or live on the animals.
This reduces species diversity directly as it destroys the pest species (normally insects), and indirectly by destroying the food source of other organisms.
• Herbicides are used to kill weeds. A weed is any plant growing in an area where it is not wanted. Weeds are destroyed as they compete with the cultivated plants for light, minerals, and water. By destroying weeds, plant diversity is reduced directly, and animal diversity may also be reduced by the removal of an important food source.
• Monoculture - many farms specialise in the production of only one crop, with many acres of land being used for the growth of one species. This has an enormous local effect in lowering biodiversity as only one species of plant is present. As relatively few animal species will be supported by only one type of plant, this results in low overall biodiversity levels. The growth of vast oil palm plantations is one of the leading causes of rainforest deforestation, leading to a loss of habitat for critically endangered species like the rhino.
climate change
In 2007, the Intergovernmental Panel on Climate Change (IPCC) released a report summarising scientists’ current understanding of climate change. The report took six years to produce and involved over 2500 scientific personnel in its production. Some of the key findings include the following:
• The warming trend over the last 50 years (about 0.13° C per decade) is nearly twice that for the previous 100 years.
• The average amount of water vapour in the atmosphere has increased since the 1980s over land and ocean. The increase is broadly consistent with the extra water vapour that warmer air can hold.
• Since 1961, the average temperature of the global ocean down to depths of 3 km has increased. The ocean has been absorbing more than 80% of the heat added to the climate system, causing seawater to expand and contributing to sea-level rise.
• The global average sea level rose by an average of 1.8 mm per year from 1961 to 2003. There is high confidence that the rate of observed sea level rise increased from the 19th to the 20th century.
• Average Arctic temperatures have increased at almost twice the global average rate in the past 100 years.
• Mountain glaciers and snow cover have declined on average in both hemispheres. Widespread decreases in glaciers and ice caps have contributed to sea-level rise.
• Long-term upward trends in the amount of precipitation have been observed over many regions from 1900 to 2005.
To enable our understanding of climate change to develop, significant quantities of data have been developed charting changes to the Earth’s climate over time. This has required an enormous international co-operative effort over many years. It is only on the basis of reliable, irrefutable evidence that decisions of an international significance can take place. Decisions made now may have far-reaching consequences for the populations of individual countries or continents today, as well as far-reaching global implications for the future.
The need to produce reliable data for issues of this scale is paramount.
Despite the weight of evidence for climate change, some scientists still believe that a causal link between human activity and climate change is yet to be established.
Global warming refers to a rise in the Earth’s mean surface temperature. The Earth’s climate has shown fluctuations in temperature throughout its history, so it is not possible to say for certain that humans are directly causing global warming. However, carbon dioxide levels in the atmosphere have significantly increased since the industrial revolution, trapping more thermal energy in the atmosphere. Therefore most scientists believe that human activities are contributing to global warming.
If global warming continues biodiversity will be affected. For example:
• The melting of the polar ice caps could lead to the extinction of the few plant and animal species living in these regions. Some species of animals present in the Arctic are migrating further and further north to find favourable conditions as their habitat shrinks.
Increasing global temperatures would allow temperate plant and animal species to live further north than currently.
-Rising sea levels from melting ice caps and the thermal expansion of oceans could flood low-lying land, reducing the available terrestrial habitats. Saltwater would flow further up rivers, reducing the habitats of freshwater plants and animals living in the river and surrounding areas.
• Higher temperatures and less rainfall would result in some plant species failing to survive, leading to drought-resistant species (xerophytes, Figure 5) becoming more dominant. The loss of non-drought-resistant species of plants would lead to the loss of some animal species dependent on them as a food source. These would be replaced by other species that feed on the xerophytes.
• Insect life cycles and populations will change as they adapt to climate change. Insects are key pollinators of many plants, so if the range of an insect changes, it could affect the lives of the plants it leaves behind, causing extinction. And as insects carry many plant and animal pathogens, if tropical insects spread, this in turn could lead to the spread of tropical diseases towards the poles.
If climate change is slow, species may have time to adapt (for example by eating a different food source) or to migrate to new areas. This will lead to a loss of native species, but in turn other species may move ino the area - so bivdiversity would not necessarily be lost. The into the area - so biodiversity would not necessarily be lost. the species mix would simply change.
