Ecology refers to the studies of fisheries, agriculture and forestry. It also relates about predicting, preventing and sorting out ecological problems occurring in an ecosystem by human activities. It enables us to have a better understanding about the physical state of our environment and the consequences of the massive environmental intervention.
The subject matter of Ecology is normally divided into four broad categories:
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Physiological Ecology – having to do with the response of single species to environmental conditions (light, temperature.)
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Population Ecology – abundance and distribution of individual species, factors causing such distribution.
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Community Ecology – number of species found at a given area and their interactions.
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Ecosystems Ecology – structure and function of the entire suite of the biotic things and their abiotic environment.
Ecology includes:
- Ecosystem
- Population
- Communities
What is an Ecosystem?
An Ecosystem is a biological environment consisting of all organisms living in a particular area, as well as, all abiotic components of the environment with which the organisms interact. Different ecosystem form the Biosphere or Ecosphere. Therefore, the ocean, land surfaces and different sphere layers form part of the Biosphere.
Example of an Ecosystem
The picture above is an example of an ecosystem which shows different types of species present in the environment.
In an ecosystem, there is constant cycling of materials or nutrients. The nutrients are derived originally from the abiotic part of an ecosystem, by the living organisms. These nutrients are latter returned back to the environment either as waste products or as dead bodies of organisms. Energy is needed to carry out these nutrient cycles. This energy is obtained ultimately from the sunlight and it is gradually lost as heat.
However, the energy flows through ecological communities, including producers and consumers (those which remove materials from the environment) and decomposer (those which return materials back to the environment).
Nitrogen Cycle in an Ecosystem
Nitrogen is the most common element in the atmosphere, having a composition of about 78 % in the air. Nitrogen is also vital for all life on Earth, because amino acids; constituent of proteins and nucleic acids; constituent of DNA (deoxyribonucleic acid), would not have existed without nitrogen. In the atmosphere, Nitrogen exists as a very stable molecule, N2, which is not used by plants and animals.
When a plant or animal dies, its tissues decompose, as a result of the action of saprotrophic bacteria. Saprotrophic bacteria and fungi are decomposers which secrete digestive enzymes onto dead organisms or their waste, thus absorbing the product of digestion as nutrients. One of the important product of this decay is ammonia (NH3, a compound of Nitrogen), which is washed into the soil. The excretory products of animals contain nitrogenous waste products such as ammonia, urea and uric acid. Their organic matter in their droppings is also decomposed by soil bacteria.
Diagram of a Nitrogen Cycle
The nitrogen cycle comprises of the following steps:
- Nitrogen fixation
- Nitrogen in primary producer food chains
- Nitrogen in decomposer food chains
- Nitrification
- Denitrification
Nitrogen fixation
The only way by which nitrogen can be made available to living things is by nitrogen fixation. Nitrogen fixation is the conversion of nitrogen gas to more reactive substances such as ammonium, NH4+ and nitrate NO3-.
Free living bacteria such asAzotobacter fix nitrogen to ammonium NH4, which they use to make their own independent supply of amino acids. Symbiotic bacteria such as Rhizobium which live in the nodules of leguminous roots also fix nitrogen. With the help of the enzyme nitrogenase, they convert nitrogen gas to NH4+ ions. They then provide the plants with some of the fixed nitrogen to make proteins. To fix nitrogen the bacteria needs:
- A supply of hydrogen
- A supply of ATP (adenosine tri phosphate)
- Anaerobic conditions
These materials are obtained from the plants.
Nitrogen and hydrogen gases react together in industries forming ammonia by the haber process. The ammonia is converted to ammonium nitrate which is the most widely used inorganic fertiliser.
During lighting, the huge quantities of energy cause nitrogen molecules to react with oxygen molecules, forming nitrogen oxides. These dissolve in rain to form nitric acid. The nitric acid when washed down into the grounds reacts with rocks forming nitrates.
Nitrogen in primary producer food chains
Nitrates formed by lighting, or applied to the soil in fertilisers are absorbed by plant roots. Inside the plant cells, NO3-, ions are reduced to NH4+ ions, which are then used to make amino acids. The NH4+ ions produced by the nitrogen fixing bacteria are used in the same way. The plants can then use the amino acids to make proteins. Animals obtain their nitrogen in the form of proteins, when they eat plants or other animals.
Nitrogen in Decomposer food chains
Many decomposers which feed on dead bodies and waste materials, such as faeces and urine from living organisms digest proteins extracellular. They secrete proteases which break down the proteins into amino acids. The decomposers may then absorb these amino acids and incorporate them into their own bodies. Some of the amino acids are deaminated by decomposers producing NH4+ ions which pass into the soil. Urea present in animal urine is also converted to ammonium in the soil. The production of ammonium ions is called ammonification.
Nitrifying bacteria in the soil oxidise the ammonium ions to nitrate ions, in two stages. The first stage is the conversion of ammonium ions to NO2- ions mainly by nitrosomonas bacteria. NO2- ions are then oxidised to NO3- ions by bacteria of the genus Nitrobacter. These bacteria derive their energy from this process and use the energy for chemosynthesis.
The conversion of ammonia to nitrites and the back to nitrates is known as the process of nitrification.
Another group of bacteria reduce NO3- ions to nitrogen gas which returns to the atmosphere. This is called denitrification and is carried out by Denitrifying bacteria such as Pseudomonas denitrificans.
This is only done in aerobic conditions in which nitrate is decomposed in order to obtain oxygen which they use in respiration. These bacteria are facultative anaerobes and are common in compost heaps, waterlogged soils and in sewage treatment plants. Like this, the nitrogen is released in the atmosphere and it can circulate again.
The Environmental Issues
Despite the worldwide growth in the environmental movement and environmental awareness, the degradation of our planet and natural resources of our island has accelerated. Our main environmental issues are as follows:
- Population Increase
- Urbanisation
- Industrialisation
- Deforestation
- Pollution
- Global warming
- Pesticides
Population Increase
This graph shows the population growth in Mauritius.
Since population has increased over the past hundred years, there have been three main changes in the environmental situation which are:
- Urbanisation
- Industrialisation
- Deforestation
This graph above shows the relationship between the growing population and the extinction of species worldwide.
As the world population continues to grow geometrically, great pressure is being placed on arable land, water, energy, and biological resources to provide an adequate supply of food while maintaining the integrity of our ecosystem. According to the World Bank and the United Nations, from 1 to 2 billion humans are now malnourished, indicating a combination of insufficient food, low incomes, and inadequate distribution of food. This is the largest number of hungry humans ever recorded in history. In China about 80 million are now malnourished and hungry. As the world population expands, the food problem will become increasingly severe, conceivably with the numbers of malnourished reaching 3 billion.More than 99 per cent of the world's food supply comes from the land, while less than 1 per cent is from oceans and other aquatic habitats. The continued production of an adequate food supply is directly dependent on ample fertile land, fresh water, energy, plus the maintenance of biodiversity. As the human population grows, the requirements for these resources also grow. Even if these resources are never depleted, on a per capital basis they will decline significantly because they must be divided among more people.
Urbanisation
The development of towns and cities makes less and less land available for wildlife. In addition the crowding of growing populations into towns leads to problems of waste disposal. The sewage and domestic waste from a town of several thousands of people can cause disease and pollution in the absence of effective means of disposal. When fuels are burned for heating they produce gases which pollute the atmosphere. There is a need of larger surface areas of land for the housing purposes. When no spaces are available, then people opt for cutting of trees. Therefore, deforestation problem is directly related to urbanisation, as well as industrialisation.
Industrialisation
In some cases, an increasing population is accompanied by an increase in manufacturing industries which produce gases and other waste products which can damage the environment. The effects of the human population on the environment are complicated and difficult to study. In their ignorance, humans have destroyed many plants and animals and great areas of natural vegetation. Industrialisation also has a great demand for land surfaces.
Deforestation
Deforestation is clearing Earth's forests on a massive scale, often resulting in damage to the quality of the land. Forests still cover about 30 percent of the world’s land area. The world’s rain forests could completely vanish in a hundred years at the current rate of deforestation.
Forests are cut down for many reasons, but most of them are related to money or to people’s need to provide for their families. The biggest driver of deforestation is agriculture. Farmers cut forests to provide more room for planting crops or grazing livestock. Often many small farmers will each clear a few acres to feed their families by cutting down trees and burning them in a process known as “slash and burn” agriculture.
Logging operations, which provide the world’s wood and paper products, also cut countless trees each year. Loggers, some of them acting illegally, also build roads to access more and more remote forests—which lead to further deforestation. Forests are also cut as a result of growing urban sprawl.
Not all deforestation is intentional. Some is caused by a combination of human and natural factors like wildfires and subsequent overgrazing, which may prevent the growth of young trees.
Deforestation has many negative effects on the environment. The most dramatic impact is a loss of habitat for millions of species. Seventy percent of Earth’s land animals and plants live in forests, and many cannot survive the deforestation that destroys their homes.
Deforestation also drives climate change. Forest soils are moist, but without protection from sun-blocking tree cover they quickly dry out. Trees also help perpetuate the water cycle by returning water vapour back into the atmosphere. Without trees to fill these roles, many former forest lands can quickly become barren deserts.
Removing trees deprives the forest of portions of its canopy, which blocks the sun’s rays during the day and holds in heat at night. This disruption leads to more extreme temperatures swings that can be harmful to plants and animals.
Trees also play a critical role in absorbing the greenhouse gases that fuel global warming. Fewer forests mean larger amounts of greenhouse gases entering the atmosphere—and increased speed and severity of global warming.
The quickest solution to deforestation would be to simply stop cutting down trees. Though deforestation rates have slowed a bit in recent years, financial realities make this unlikely to occur.
A more workable solution is to carefully manage forest resources by eliminating clear-cutting to make sure that forest environments remain intact. The cutting that does occur should be balanced by the planting of enough young trees to replace the older ones felled in any given forest. The number of new tree plantations is growing each year, but their total still equals a tiny fraction of the Earth’s forested land.
Soil erosion and flooding are another causes of deforestation which have taken place in Mauritius, at Mon Gout Ilot Pamplemousses flood on 26 March 2008.
The Mauritian government has taken all these problems into consideration and has taken important decisions for the environment concerning the floods.
Cabinet has taken note that, as recommended by the Ministerial Committee set up to monitor the implementation of the recommendations of the fact finding committee on the cyclone ex-Lola flooding, the Drains Management committee has been established under the chairmanship of the permanent secretary of Ministry of Local government, Rodrigues and outer island to:
- Monitor progress in the construction and maintenance of drains
- Ensure the effectiveness of land drainage projects,
- Recommend preventive measures to mitigate flooding
Pollution
Pollution is not a new problem. For hundreds of years we have been aware of the devastating effects of smoke in the atmosphere. But to-day questions about pollution and conservation are becoming increasingly important to many countries. We are more aware of the consequences of our actions with regard to the health of our planet and all its living forms. To-day the sun is rising on the planet far more crowded, degraded, and polluted than it was before. By every major indicator, the planet’s physical condition has deteriorated. Regrettably, we are losing the battle. Scientists discovered that the seemingly harmless chlorofluorocarbons (CFCs) used in refrigerators, air conditioners, aerosol cans, and plastic foams were depleting the stratospheric ozone layer that protects us from harmful ultra-violet radiation. Tropical deforestation was not a worry. The greenhouse effect was widely accepted scientific hypothesis, but there was little evidence of global warming.
Air Pollution
Some factories and all motor vehicles release poisonous substances into the air. Factories produce smoke, sulphur dioxide; cars produce lead compounds, carbon monoxide and the oxides of nitrogen which lead to smog.
Smoke
This consists mainly of tiny particles of carbon and tar which come from burning coal either in power stations or in the home. The tarry drops contain chemicals which may cause cancer. When the carbon particles settle, they blacken buildings and damage the leaves of trees. Smoke in the atmosphere cuts down the amount of sunlight reaching the ground.
Particulates
Although smoke has been largely eliminated from our towns, vehicle exhausts gases (particularly from diesels), contain microscopic particles coated with hydrocarbons. The particles may be referred to as PM10s or PM2.5s because their diameters are less than 10 or 2.5 micrometres respectively. The particles are thought to be a cause of about 10,000 deaths per year. Particularly of people already suffering from chronic lung diseases such as emphysema and bronchitis.
Sulphur dioxide and oxides of nitrogen
Coal and oil contain sulphur. When these fuels are burned, they release sulphure dioxide into the air. Although the tallchimneys of factories send smoke and sulphur dioxide high into the air, the sulphur dioxide dissolves in rain water and forms an acid. When this acid falls on buildings, it slowly dissolves the limestone and mortar. When it falls on plants it reduces their growth and damages their leaves.
Oxides of nitrogen from power stations and vehicle exhausts also contribute to atmospheric pollution and acid rain. The nitrogen oxides dissolve in rain drops and form nitric acid.
Oxide of nitrogen also takes part in reactions with other atmospheric pollutants and produce ozone. It may be the ozone anew the nitrogen oxides which are largely responsible for the damage observed in forests.
One effect of acid rain is that it dissolves out the aluminium salts in the sols. These salts eventually reach toxic levels in streams and lakes
There are still some arguments about the source of the acid gases which produce acid rain. For example a large proportion of the sulphur dioxide in the atmosphere comes from natural activities of certain marine algae. These macroscopic ‘plants’ produce the gas, dimenthylsulphide, which is oxidized to sulphur dioxide in the air.
Nevertheless, there is considerable circumstantial evidence that industrial activities in European Countries add large amounts of extra sulphur dioxide and nitrogen oxides to the atmosphere.
Smog
This is a thin fog which occurs in cities in certain climatic conditions. Smog is irritating to the eyes and lungs and also damages plants. It is produces when sunlight and ozone in the atmosphere act on the oxides of nitrogen and unburnt hydrocarbons released from vehicle exhaust. This type of smog is called ‘photochemical smog’ to distinguish it from smoke plus fog.
Carbon monoxide
This gas is also a product of combustion in the engines of cars and trucks. When inhaled, carbon monoxide combines with haemoglobin in the blood to form a fairly stable compound, carboxyhaemoglobin. The formation of carboxyhaemoglobin reduces the oxygen-carrying capacity of the blood and this can be harmful, particularly in people with heart disease or anaemia.
A smoker is likely to inhale far more carbon monoxide from cigarettes than from the atmosphere. Nevertheless, the carbon monoxide levels produced by heavy traffic in towns can be harmful.
Chlorofluorocarbons
These are gases which readily liquefy when compressed. This makes them useful as refrigerants, propellants in aerosol cans and in plastic foams. Chlorofluorocarbons are very stable and accumulate in the atmosphere, here they react with ozone.
Ozone is present throughout the atmosphere but reaches a peak at about 25 Km, where it forms what is called the ‘ozone layer’. This layer filters out much of the ultraviolet radiation in sunlight.
The chorine from CFCs reacts with ozone and reduces its concentration in the ozone layer. As a result, more ultraviolet radiation reaches the Earth’s surface. Higher levels of skin cancer. It can also affect crops, damage marine plankton and even distort weather patterns.
The reactions involved are very complex. There are also natural processes which destroy or generate ozone.
Greenhouse & Global Warming
The Earth surface receives and absorbs radiant heat from the Sun. It re-radiates some of this heat back into space. The Sum’s radiation is mainly in the form of short-wavelength energy and penetrates our atmosphere easily. The energy radiated back from the earth is in the form of long wavelengths (Infrared), much of which is absorbed by the atmosphere. The atmosphere acts like the glass in a greenhouse. It lets in light and heat from the sun, but reduces the amount of heat which escapes. If it were not for this ‘Greenhouse Effect’ of the atmosphere, the Earth’s surface would probably be at -18°C. The ‘greenhouse effect’, therefore, is entirely natural and desirable.
Not all the atmosphere gases are equally effective at absorbing IR radiation. Oxygen and nitrogen, for example absorb little ore or none. The gases which absorb most IR radiation, in order of maximum absorption, are water vapour, carbon dioxide, methane and atmospheric pollutants such as oxides of nitrogen and CFCs. Apart from water vapour, these gases are in very low concentrations in the atmosphere, but some of them are strong absorbers of IR radiation. It is assumed that if the concentration of any of these gases were to increase, the greenhouse effect would be enhanced and the Earth would get warmer.
In recent years, attention has focused principally CO2. If you look back at the carbon cycle, you will see that the natural processes of photosynthesis, respiration and decay would be expected to keep the CO2concentration at a steady level. However, since the Industrial Revolution, we have been burning the fossil fuels derived from coal and petroleum and releasing extra CO2 into the atmosphere. As a result, the concentration of CO2 has increased. And is likely to go on increasing as we burn more and more fossil fuel.
Conservation
Coal, oil, natural gas and minerals cannot be replaced once their sources have been totally depleted. Estimates of how long these stocks will last are unreliable but in some cases e.g., lead and tin, they are less than 100 years.
By the time that fossil fuels run out, we will have to have alternative sources of energy. Even the uranium used in nuclear reactors is a finite resource and will one day, run out.
The alternative sources of energy available to us are hydro-electric, nuclear, wind and wave power, wood and other plant products. The first two are well established; the others are either in the experimental stages, making only small contribution, or are more expensive than fossil fuels.
Plants products are renewable resources and include alcohol distilled from fermented sugar, which can replace or supplement petrol, and sunflower oil, which can replace diesel fuel; and wood from fast growing trees. In addition. Plant and animal waste material can be decomposed anaerobically in fermenters to produce biogas, which consists largely of methane.
Recycling
As minerals and other resources become scarcer, they also become more expensive. It then pays to use them more than once. The recycling of materials may also reduce the amount of energy used in manufacturing. In turn this helps to conserve fuels and reduce pollution.
Manufacturing glass bottles uses about three times more energy than if they were collected, sorted, cleaned and re-used. Recycling the glass from bottles does not save energy but does reduce the demand for sand used in glass manufacture.
Waste Paper can be pulped and used again, mainly for making paper and cardboard. Newspapers are deinked and used again for newsprint. One tonne of waste paper is equivalent to perhaps 17 trees. So collecting waste paper may help to cut our import bill for timber and spare a few more hectares of moorland from the spread of commercial forestry.