1. Levels of Ecological Organization
1.1 What is Ecology?
The world ecology is derived from 2 Greek words “oikos” (meaning house or living space) and “logos” (meaning study). Ecology is the study of the relationships of living organisms with each other and their surroundings, both physical (abiotic or non-living) and biological (biotic or living) environment. The interactions between organisms and environment influence the distribution and abundance of living things and these interactions are essential because there is only one source of energy, the sun. All living organisms depend on the flow of solar energy through photosynthesis to support lives.
There are 4 approaches to ecology. The ecosystem approach focuses on flow of energy and nutrient cycling, relevant to the study of pollution and its effects. Community approach deals with the biotic components of ecosystems and is relevant to conservation management. Population approach focuses on population growth and maintenance and is relevant to understanding pest outbreaks. The habitat approach focuses on the physical conditions and some biological factors and their influence on presence and survival of organisms.
1.2 Levels of Organization
1.2.1 Terms
Habitat is the physical environment where individual organisms live. It describes only the physical area in the ecosystem where the organism lives (address or location). An example of a habitat is the freshwater pond. Earth has 4 habitats and they are marine, estuarine, freshwater and terrestrial.
Niche is the place and role played by an organism. It refers to where and how an organism lives and the role it plays in the ecosystem which is determined by its nutritional requirements, habits and interactions with other species. Only one species should occupy a specific ecological niche at one time to avoid competition. Generally, the breadth of the niche varies depending on the adaptability of the species, the more adaptable species occupying a wider niche than the less adaptable or more specialized species. Fundamental niche refers to the range of conditions a species can tolerate but the realized niche is the actual range the species occupies in nature, considering competition and predation etc.
Population refers to a group of organisms of the same species, all occupying a particular area at the same time, usually isolated to some degree from other similar groups. It is considered as interbreeding individuals of a species within the same area.
Community is made of any group of organisms belonging to a number of different species that coexist in the same habitat or area and interact through trophic and spatial relationships. It may constantly change dynamically as species enter or leave the location due to changes, succession or catastrophe.
Ecosystem is a complete life-supporting environment of living or biotic components together with the non-living or abiotic components through which energy flows and nutrient cycles. Abiotic components include physical, chemical and edaphic (soil-related) factors. Biotic components include intraspecific and interspecific relationships (e.g. parasitism, predator-prey relationships and symbiosis) and habitat and niches. An ecosystem comprises of several habitats and their associated communities.
1.2.2 What are producers, consumers and decomposers?
Producers (autotrophs) which include green plants and photosynthetic bacteria that harness energy from the sun to build up their organic materials from simple inorganic raw materials via photosynthesis.
Consumers (heterotrophs) can be primary or secondary. The former are herbivores that consume primary producers and the latter feed on primary consumers.
Decomposers and detritivores are consumers that derive their energy from organic wastes and dead organisms. This group includes scavengers such as cockroaches and they form a major link between primary producers and higher level consumers. Examples of this group of organisms are bacteria, fungi, earthworms, termites and small insects. Their role is to prevent accumulation of dead organic material by breaking it down and returning resulting minerals and simple organic compounds to the soil in the form of humus.
1.2.3 What is trophic level and food chain?
Trophic level refers to a stage in the food chain at which organisms obtain their food. Trophic levels provide a framework to understanding energy flow through the ecosystem. Organisms whose food is obtained from plants by the same number of steps in a food chain belong to the same trophic level.
Food chain refers to the linear relationship of different trophic levels within an ecosystem and it shows the transfer of food energy from producers through a series of organisms with repeated eating and being eaten. Usually, not more than 4 trophic levels can be supported in one chain due to huge loss of energy between trophic levels.
Food webs comprises of interconnected food chains; since each organism may be the food of more than one organism or may feed from more than one food chain. Hence, food chain intersect to produce complicated network of food webs.
1.3 Biotic Factors in an Ecosystem
Symbiosis is the association of 2 or more organisms of different species living together and there are generally 3 types of symbiosis: parasitism, mutualism and commensalism
In parasitism, parasites live in the host for most of the time and depend on the host for food, resulting in the host getting harmed with only the parasites benefiting.
In mutualism, 2 species live in close association with both benefitting from each other.
In commensalism, 2 species live in close association with the commensal benefiting while the host is not harmed.
Competition occurs when 2 species compete directly for exactly the same living resources resulting in the more efficient species eliminating the other. The 2 species will compete until one becomes extinct or niche differentiation is achieved.
Predator-prey relationship has a typical characteristic of having cyclic fluctuations that occur in members of the 2 species being slightly out of phase with each other.
1.4 Abiotic factors in an ecosystem
These include physical, chemical and edaphic factors. Physical factors are temperature, light, rainfall, wind and water currents, and catastrophe. Chemical factors include gases, pH, salinity and minerals. Edaphic factors are those related to soil.
2. Recycling of Nutrients
Living organisms require more than a supply of energy as they also require materials from which to build their bodies. Living organisms are built from a relatively small number of different kinds of atoms and of these; carbon, hydrogen, oxygen and nitrogen are the most common. Plants are able to make use of inorganic sources of these atoms. They can use carbon dioxide from the air and water from the soil to provide carbon, oxygen and hydrogen atoms to make carbohydrates. They use nitrate and ammonium ions to supply nitrogen atoms to make proteins. Unlike plants, animals obtain most of the atoms from organic molecules they eat. We have a continuous supply of energy from the sun but supply of materials like nitrogen, carbon etc are limited. Since living organisms require these materials, they have to be recycled.
2.1 Carbon Cycle
Carbon is an important component of carbohydrates, fats and proteins which are important constituents of the living organisms. The atmosphere is a large vital carbon reservoir despite having a mere concentration of 0.04% content of carbon dioxide. Autotrophs (green plants, algae, blue-green bacteria) use the atmospheric carbon dioxide and via the process of photosynthesis, incorporate it into their biomass. The resulting organic matter will become a carbon source for the heterotrophs. However, not all plants are eaten by other animals hence waste materials and dead bodies are used as food sources for decomposers such as fungi and bacteria. When both plants and animals respire, a portion of this carbon is returned to the atmosphere as carbon dioxide. In water, carbon dioxide from the air dissolves in water to produce bicarbonate ions which are used by aquatic autotrophs as a carbon source. The ocean contains 50 times the amount of carbon dioxide as that of the atmosphere.
In conditions where dead plant material cannot be rapidly broken down by decomposers, such as where solids are waterlogged and oxygen in short supply, decay may only be partial and vast quantities of semi-decayed material accumulate and form peat. These accumulating peat deposits and organic sediments may in the long term generate new “fossil” fuel deposits in a process termed as carbonification. Many marine organisms have shells containing calcium carbonate and when these organisms die, their shells fall to the sea bed. Huge deposits of such shells built up over thousands of years to form limestone rocks. Earth movements may carry these rocks deep into the earth from where the carbon atoms may be returned to the atmosphere by volcanic eruptions which release carbon dioxide.
When fossil fuels are burnt, carbon dioxide is released. This rising atmospheric carbon dioxide concentration (greenhouse effect) leads to global warming. Deforestation is another cause for the increase in the level of atmospheric carbon dioxide as less vegetation is used to remove carbon dioxide for photosynthesis.
2.2 Nitrogen Cycle
Nitrogen being the principle component of proteins, nucleic acids, is an essential element required to sustain life. Air is comprised of 79% nitrogen gas by volume; however, this is not utilizable. Nitrogen gas is made up of 2 N atoms bonded together by 3 covalent bonds and this makes it very stable and chemically inert (unreactive). Before nitrogen can be used by living organisms, it has to undergo nitrogen fixation. Nitrogen cycle comprises of the following 4 steps.
2.2.1 Nitrogen Fixation
This is the conversion of free nitrogen into nitrogen compounds. Nitrogen occurs in huge quantities in the air but most organisms cannot use atmospheric nitrogen. This nitrogen must first be converted to absorbable nitrogen compounds by a process called nitrogen fixation. In nature, little nitrogen fixation occurs during thunderstorms. Lightning provides the energy to oxidize nitrogen to nitrogen oxides. Nitrogen fixation can also be carried out by nitrogen-fixing bacteria such as Azobacter and Clostridium which live free in the soil; Rhizobium which lives mutualistically in root nodules on leguminous plants (like beans, sweet peas, clover). Nitrogen-fixing bacteria possess nitrogenase an enzyme that enables them to reduce nitrogen to ammonia or ammonium compounds. Nitrogen fixation can also be done artificially in industry by a process called Haber process.
2.2.2 Ammonification / Decomposition
This is a process of converting organic compounds to ammonia. Ammonia is produced in ecosystems from organic nitrogen-containing compounds. These compounds occur in faeces, nitrogenous excretory products such as urea and the dead bodies of organisms. Ammonification is carried out by putrefying bacteria and fungi which act as decomposers in ecosystems, breaking down the bodies of dead organisms. This process is important as it recycles large amounts of nitrogen to the soil.
2.2.3 Nitrification
It involves the conversion of ammonium ions to nitrites and nitrates. Ammonium ions in the soil or water are oxidized to nitrites and nitrates by nitrifying bacteria like Nitrosomonas which oxidizes ammonia to nitrite and Nitrobacter which oxidizes nitrite to nitrate. These bacteria obtain energy from the redox reactions which is involved in nitrification which requires oxygen, thus it happens most rapidly in well aerated soils or well-oxygenated bodies of water. The nitrate ions produced by nitrification can be taken up by plants to make proteins. Consumers obtain their nitrogen in the form of proteins when they eat plants or animals.
2.2.4 Denitrification
It involves the conversion of nitrates back to atmospheric nitrogen. The nitrogen cycle is completed by denitrifying bacteria such as Pseudomonas which lives in conditions of low oxygen and they reverse the nitrifying process, converting nitrates to nitrogen gas. This denitrification leads to the loss of nitrogen from the biotic component of the ecosystem to the atmosphere.
3. Energy Flow through the Ecosystem
3.1 Laws of Thermodynamics
The 1st Law of thermodynamics states that energy may be transformed from one form to another but is neither created nor destroyed.
The 2nd Law of thermodynamics states that energy conversion can never be 100% efficient and some energy may escape as heat.
3.2 Energy Flow
Organisms of the ecosystem are linked by their energy and nutrient relationship. The energy that powers most ecosystems is ultimately derived from the sun. Constant recycling of nutrient occurs in an ecosystem. While the chemicals in the ecosystem are constantly recycled, some of the energy transferred within is changed into forms which cannot be used again by the system.
3.3 Energy losses in Food Webs
As energy is transferred from one organism to another in a food web, a large proportion of it is lost to the surrounding. In a pond, for example, a certain amount of sunlight falls on to the water surface and a portion of this energy is converted to chemical energy by producers. The producers use some of this energy themselves e.g. for active transport but some of this energy is lost in the form of heat energy
When these producers are eaten by herbivores, not all the energy in the producers can be used by herbivores because not all parts of the plant are edible or it may not be possible for herbivores to digest and absorb all of the plant material they eat. On the average, in a terrestrial food web, only about 10% of the energy in the producers will be transferred to the herbivores. The percentage is larger in the aquatic food web
The herbivores will use some of this energy, for processes such as moving and active transport but once again, a high proportion of the energy will be lost to the environment as heat. Only a small proportion of the energy is transferred to the herbivores is available to be transferred to the carnivores. This pattern continues along the food chain, with approximately 90% of the energy being lost at each transfer between trophic level.
3.4 Conservation of Solar Energy
Energy from the sun is taken as 100%. About 40% is reflected and 15% is used as heat energy to heat things up. The remaining 45% is by absorption by earth’s surface or by plants. Of this 45%, 2/3 is radiated from the surface and heats up the atmosphere. The remaining 1/3 is available to plants as photosynthetically active radiation and as heat loss.
Less than 1% of solar energy is used in photosynthesis and transformed into the chemical energy of plant tissues.
Production is defined as what has been produced and is measured as the standing biomass which is the biomass at the time of sampling or at a given moment in time. Biomass refers to the combined dry weight of all organic matter contained in all organisms per unit area of ground or per unit volume of water. It is usually expressed in units of dry mass (tones per hectare) or in units of energy (kJ/m2). Biomass is measured as the dry weight of organisms because the water they contain is not a source of energy. When organisms’ dry weight is required, how is it possible to measure its biomass while it is alive?
Productivity is the rate of production of standing biomass. It is a measure of the amount of energy incorporated into the organisms in the trophic level, in a given area, over a certain period of time. The rate at which producers convert light into chemical energy is called primary productivity. Primary productivity determines the total energy flow through the system and hence the amount of life the ecosystem can support.
3.4.1 Gross Primary Productivity (GPP)
It is a measure of the total production of organic matter by green plants per unit area per unit time during photosynthesis. It does not represent the actual amount of food available for heterotrophs because some of the organic matters are used for the plants’ respiration and metabolism needs. It is measured in units of energy or dry organic mass.
3.4.2 Net Primary Productivity (NPP)
NPP is the rate at which autotrophs store organic materials as new tissue. Glucose molecules produced in photosynthesis are used to provide energy for maintenance and growth. Energy is lost as heat from plants during respiration. The rest is deposited in various forms in and around cells and represents stored dry mass.
Thus NPP corresponds to GPP minus plant respiration rate (R). NPP represents food energy potentially available to heterotrophs.
3.4.3 Secondary Productivity
It is the rate at which energy is used to make new consumer tissue. It is also the rate at which consumers and decomposers in the food chains accumulate dry mass (or biomass) or energy. Productivity declines with each transfer of energy through the trophic level. Secondary production refers to the mass or energy available to the next trophic level. Secondary production, P = Ingestion – egestion – respiration – urine.
3.4.4 The 10% law
A study done on energy flow showed that energy taken in by the animals at one trophic level was about 10% of the energy taken in by the animals at the previous trophic level. In another words, about 10% of primary consumer material is converted to secondary consumer material which in turn can only have about 10% of its material changed into the organism at the next trophic level.
Since there is a great loss of energy along the food chain, it seldom includes more than 4 trophic levels and each trophic level usually contains fewer organisms and of a smaller biomass than the preceding trophic level. This 10% law only applies to food taken in by mouth by animals, the transfer of energy between primary and secondary consumers and to tertiary consumers and to whole trophic levels. It does not apply to an individual and also does not apply to energy transfer between plants and primary consumers which eat them.
3.5 Trophic Organization
Each ecosystem has a trophic structure which represents the different feeding relationships that determines the route of energy flow and the pattern of chemical cycling. Ecologists divide the species in a community or ecosystem into 5 trophic levels based on their main source of nutrition. Primary producers, primary consumers, secondary consumers, tertiary consumers and decomposers.
Primary producers are photosynthetic autotrophs and they determine the entire energy budget of an ecosystem since they are the only ones that utilize solar energy. Primary consumers are herbivores that eat the primary producers. Secondary consumers are carnivores that eat herbivores. Tertiary consumers are carnivores that eat other carnivores. Decomposers are consumers that derive their energy from organic wastes and dead organisms. They digest food outside their bodies by secreting enzymes into the environment. These organisms include scavengers such as cockroaches and eagles. Detritus feeders consume dead organic matter, extract some of the energy stored within in and excrete it in a further decomposed state.
3.6 Food Chains and Food Webs
A food chain involves the transfer of food from one trophic level to another. Food chains are usually limited to 3 to 4 links due to the loss of energy at every transfer of it from one level to another. Biomass at the apex may not be sufficient to support another level leading to top-level consumers having a high possibility of getting extinct. Organisms at the higher trophic levels are usually bigger in size and they require even more energy to support and maintain their existence.
Food web is made up of interconnecting food chains in a community and it describes the actual feeding relationships within a given community more accurately than a food chain. Some animals, being omnivores, play different roles at different times e.g. they can be primary consumer and secondary or tertiary consumers at different times.
3.7 Ecological Pyramids
Food webs give a useful description of the feeding relationships in a community but it is not quantifiable. Ecological pyramids give a quantification of feeding relationships as they involve obtaining numerical data on the accumulation of organic matter by the producers, consumers and decomposers.
Ecological pyramids are useful in providing comparisons of different ecosystems and allowing analysis of how an ecosystem responds to abnormal conditions such as pollution. It also provides information necessary for the assessment of the potential of an ecosystem for food production.
There are many ways of looking at ecological pyramids – in terms of numbers, biomass or energy content. The pyramid shape that results from the inefficiency of energy transfer shows the pattern of energy usage by the members of each trophic level.
3.7.1 Pyramids of Numbers
As its name suggests, it illustrates the numbers of organisms at each trophic level at any one time. It is constructed using the number of organisms per unit area at each trophic level. Each level is represented by a horizontal bar and the length of each bar represents the number of organisms at that particular level. The bar at the base indicates the number of producers, above that the number of primary consumers, above which the secondary consumers and so on. The dentritivores and decomposers and parasites may not be included. In most communities, there are more primary producers than primary consumers and more primary consumers than secondary consumers etc, resulting in an upright pyramid.
The advantage is that date to construct the pyramid can be obtained relatively easily.
The limitations are as follows. All organisms are taken to be equal regardless of size so an oak tree is counted as one and so is an aphid. No account is made for juveniles and other immature form of a species whose diet and energy requirements may differ from the adult. The numbers of some organisms are so huge that they cannot be represented accurately on the same scale as other organisms of different trophic levels.
Some of the above limitations can be overcome by using the biomass of organisms rather than their numbers.
3.7.2 Pyramids of Biomass
These represent the biomass of each trophic level at any one time in a given unit area where biomass equals the total dry weight of organisms (number of individual organism multiplied by mass of each organism). Generally, the shape is a broad base with a narrow top, due to the inefficient energy transfer. Organisms at the lower trophic level have a larger biomass to support those at the higher trophic levels. This takes into account of the size of organisms and it is reflective of terrestrial ecosystem.
The advantage is that it is more likely to produce a pyramid shaped chart than pyramid of numbers.
The limitations are as follows. Inverted pyramids of biomass may still occur in open water and deep water where the producers are small and short-lived (high turnover) e.g. zooplankton consume phytoplankton so rapidly that the producers do not have a chance to build up a large population size or standing crop. The biomass may not equal to the energy value and biomass is a measurement of dry weight hence only dead organisms weight can be taken.
3.7.3 Pyramids of Energy
This involves the measurement of energy produced per unit area by each trophic level over a given period of time. The length of the producer bar is proportional to the amount of solar energy used annually in photosynthesis. The other bars show the rate at which energy passes along the food chain.
The advantages are as follows. The energy pyramid indicates the amount of energy required to support each trophic level and the amount of energy loss, but not in pyramid of numbers or biomass. They are neither inverted nor having a central bulge. There is no need to consider numbers or differences in size because all organisms can be converted to their energy equivalente rate of productivity of individual organisms within an ecosystem.
The limitations is that the pyramid of energy is relatively time-consuming and troublesome to obtain involving destructive sampling.
3.7.4 General Advantages of Ecological Pyramids
The pyramids provide for quantitative visual representation of data. The pyramids convey the relative importance of various trophic levels
3.7.5 General Criticisms of Ecological Pyramids
The pyramids of numbers, biomass and energy described depend on assigning living organisms to trophic levels. Although the correct level is obvious for plants and obligate herbivores, many carnivores and omnivores have varied diet and thus their trophic level varies according to the food selected, which may in turn be an animal with a range of possible trophic levels.
Dead organic materials (DOM) are important food source. Up to 80% of the energy fixed by terrestrial plants enters decay pathways rather tha being passed on to herbivores. It is difficult to fit detritivores and its consumers into conventional pyramids though the energy flow within these pathways is high.
3.7.6 Difference between Energy Flow and Nutrient Cycling in Ecosystems
The earth receives a continuous and unlimited supply of solar energy. The supply of nutrients such as carbon, nitrogen and phosphorus is limited in an ecosystem.
Energy flow is in a linear fashion along the food chain at trophic levels. Nutrients such as carbon and nitrogen occur in global cycles.
Energy cannot be created nor destroyed but can be converted from one form to another. Eventually, all energy is lost as heat to the environment at each trophic level as organisms cannot use heat as a source of energy. For nutrient cycling, nothing is lost but reused and recycled over and over again in ecosystems. Nutrients in organic form eventually return either as waste products or as the dead bodies of organisms back to the environment.
For energy flow, solar energy is absorbed during photosynthesis in order to supply energy required in the endergonic reduction of atmospheric / inorganic carbon dioxide to organic carbon compounds. Solar energy is converted to and stored as chemical energy which is useful to plants and heterotrophs. For nutrient cycling, solar energy drives the nutrient cycles as the former regulates abiotic components such as temperature, movement of atmosphere, evaporation and rainfall. Nutrients are derived originally from the abiotic components of the ecosystem to be converted to plant proteins and animal proteins. Carbon and nitrogen are major elements in amino acids and proteins.
4. Effects of Human Activities
4.1 Human Impacts on the Ecosystem
As human culture has developed over the centuries, the impact we made on the ecosystem has become greater as greater. For example, as new tools are invented, hunting of animals becomes easier, leading to their extinction. Another example is the development of agriculture, which leads to the removal of natural vegetation and with the use of pesticides; it has affected natural communities as well as organisms on the farmland.
The industrial revolution ked to an upsurge in the demand for energy and other resources, which increased the amount of land disturbed by the extraction of materials such as fossil fuels, metal ores and gravel. As more fossil fuels are burnt, they release large amounts of gases such as carbon dioxide, sulphur dioxide into the atmosphere.
The growing human population and the expectation of better living conditions and easier transport has led to building of larger cities and more roads. Pollution of water, land and air by human wastes and exhaust gases from vehicles has increased.
4.2 Fossil Fuels
These are forms of stored energy. Plants are solar energy collectors and they convert solar energy to chemical energy through photosynthesis. The fossil fuels were created from incomplete biological decomposition of dead organic matter (mostly plants and marine organisms). When organic matter is buried and escapes oxidation, it can be converted by complex chemical reactions to hydrocarbons and to fossil fuels. The main fossil fuels i.e. coal, crude oil and natural gas, are our primary energy sources because on the worldwide basis, they provide approximately 90% of the energy consumed.
4.2.1 Coal
It originated as partially decomposed plant matter which is buried deeply in a sedimentary environment. Over time, heat and pressure converted the organic matter into peat, then into solid, brittle carbonaceous rock we called coal, an organic material, when burnt, produces light and heat. Coal is the world’s most abundant fossil fuel. The energy from coal is ancient solar energy trapped by plants and stored in the bonds between the carbon atoms.
4.2.1.1 Environmental Impacts of Coal Mining
Most coal mining in the U.S. is done by strip mining, a type of surface mining in which the overlaying layer of rock and soil is stripped off to reach the coal. Strip mining will cause the mine waste to be eroded away and spilled into streams and lakes, destroying fish habitat, recreational sites and reservoirs that supply water for human use. Mining also creates dust and noise and destroys wildlife habitat. In addition to surface mining, underground mining still accounts for 40% of the coal mined in U.S. With underground mining, drainage from the mines and waste piles has polluted many kilometers of streams. In underground mining, accidents like the collapse of the mines occurred, often killing many workers. Cola fires in underground mines produce smoke and hazardous fumes causing people who live near the mines to suffer from respiratory disease.
4.2.1.2 Solutions
There should be less reliance on fossil fuels and more on renewable sources like solar power and wind power. We have to educate and persuade more people to use less fuels and to reduce dependence in many energy consuming devices (like air-conditioning).
Regulations of government attempt to solve such problems. For example, the Surface Mining Control and Reclamation Act of 1977 required that mine land to be restored to pre-mining use. Reclamation Acts include proper disposing of waste, contouring the land (preventing erosion), replacing vegetation, controlling on-site erosion and acid contamination of nearby lakes and streams. International cooperation and political will states that all nations, especially the rich ones, should cut down fossil fuel emissions and help developing countries through collaboration and research to move away from fossil fuel dependence.
4.2.2 Oil and Natural Gas
Please refer to a G.C.E. “O” level Geography text book for related information.
4.2.3 Deforestation
4.2.3.1 Causes
There is the slash and burn culture where the farmer cuts the trees, tills the land for a few years then abandons it, leaving it to fallow for up to 7 years.
Fire is used as a tool to slash and burn farming. Fire can also be caused by dry weather condition in equatorial region.
There are cattle ranching. With the increased demand for hamburgers, cattle rangers in the U.S. are clearing away the forest and converting them to grazing lands. Next time you bite a hamburger, you should reflect on the fact that you may be contributing to deforestation.
There is also the gathering of fire wood where the wood is used directly for firewood.
There is also industrial logging. Commercial logging in tropical regions is wasteful and inefficient because more than 55% of the trees are damaged in the process of logging.
4.2.3.2 Effects of Deforestation
There is loss of cultural diversity. Due to deforestation, forest dwellers are affected and they would have been driven away from the forest or may even become extinct.
There is also the loss of natural habitats and biodiversity. Destruction of the tropical rainforest where biodiversity is the greatest, contributes directly to a reduction in global diversity.
There is a loss of gene pools.
Food sources and other forest products are also vanishing. Mangroves provide spawning sites for many commercially important marine animals such as crabs, prawns, shellfish and fish. If cleared, drying of rivers and streams and erosion of the shoreline may result. Food supply from aquatic ecosystem will decrease. Other forest products like pharmaceuticals, fruits etc will be depleted.
There will be a loss of carbon storage capacity. Plants help to regulate / moderate the amount of carbon dioxide by storing carbon in organic compounds. Carbon dioxide has an insulating capacity to the atmosphere and helps to reduce heat loss to outer space and thus is termed as a greenhouse gas. When forests are burnt, there is increased release of greenhouse gases, causing the temperature of the earth’s surface to increase. It also causes changes in weather patterns, sea levels and natural cycles.
There also will be climate change. When the forest is removed, radiation of heat is increased, causing global warming. The increased global temperature could cause polar ice caps to melt and the major cities on our coasts to be destroyed by floods.
There will be soil destabilization. This is a result of soil erosion caused by absence of trees. Soil structure is no longer stabilized by tree root systems.
4.2.3.3 Solutions (Conservation efforts)
We need reforestation. This involves natural reseeding which leaves few mature wind-firm trees intact as seed source. There can also be aerial seeding involving seeds sown from planes. We can also plant young trees instead of growing them from seedling to ensure successful growth.
We also need forest management. We can limit access to certain areas in the forest. We can use alternative cutting rather than cutting all trees at the same time. We can replant quick-growing species. We can also develop genetically superior trees which are faster growing and better disease-resistant. Finally, we can establish seed banks t maintain a good gene pool of species.
We need a conservation of complete habitats for example the national parks, forest reserves and botanic gardens. The preservation of individual species inadvertently saves whole habitats.
We need to find wood substitutes and reduce demand on wood related products by recycling paper and reducing paper packaging.
4.3 Conservation versus Production Challenges
Only 20% of the earth surface is suitable for grazing and 10% for growing crops. There is a challenge to produce enough food to feed the whole world’s population; not only to produce sufficient quantity but also to produce batter quality food (rich in proteins, vitamins and minerals) to avoid malnutrition. In addition, consideration to store food has to be made to reduce wastage after harvest. The next challenge then is to address the equitable distribution of food throughout the country and the world.
Crop yield potentials may be increased by careful use of fertilizers, pesticides, expanded irrigation and better farming practices. But with the use of these methods, how will that affect conservation?
4.4 Nitrogenous Fertilizers
Nitrogen is vital to the growth of plants. It is part of all the essential constituents of cells (chlorophyll, nucleic acids, proteins and cell walls).
Nitrogenous fertilizers are commonly used by farmers to increase the yield of their crops. There is an optimum level at which fertilizers are used, beyond this level; applying extra nitrogenous fertilizers cease to be worthwhile. Thus farmers must know when and how much to apply in order to achieve the desired outcome. When farmers apply fertilizers above the optimum, this will contribute to nitrate pollution. There is a correlation between increased nitrate fertilizers and the rise in nitrate concentrations in drinking water. Nitrogenous fertilizers have been blamed for causing cancer, cyanosis in infants and growth of toxic algae in rivers and seas.
4.4.1 How nitrogenous fertilizers influence the yield of crops?
As for leaf area, nitrogen may make leaves larger, increasing surface area to trap more light and rate at which cells multiply and the size of cells.
In crop development, skillful timing of fertilizer may encourage development of flowers and yield of grain.
As for crop quality, sometimes quality is more important than yield. For example, brewers need barley to make malt but they need grain with as little protein as possible.
There are also side effects. For example, extra growth of leaves means extra weight for stems, increasing stress on stems. Enlarged cells make them more succulent and prone to insect attack.
4.4.2 Effects of Nitrogen Pollution
There is eutrophication (nitrogen enrichment). Due to leaching of nitrates into water bodies such as rivers and lakes, plants may grow in excess thus narrowing water bodies, overlaying and damaging banks, clogging water supply conduits and damaging machinery such as propellers of boats. It may also cause excessive growth of algae which are unsightly and may be toxic. When algae die, the bacteria that feed on them use up oxygen leading to a decrease in oxygen level which may cause organisms to die, resulting in ecological imbalance of the river.
There is soil acidification.
There is also a threat to plant species. It may cause extinction of species adapted to low nitrogen supply.
Finally, there is contamination of water resources / drinking water (nitrate toxicology). There is a concern for infant health. Infants’ feed made with water with more than 50 mg of nitrate per litre is believed to involve a risk of attacks of acute infant methaemoglobinaemia (nitrate transforming oxyhaemoglobin into inactive methaemoglobin which does not carry oxygen leading to “blue babies”). There is a concern that nitrate may react with food components to give carcinogenic compounds. Finally, there is a concern that nitrate may cause a variety of other disease like goiter (interfering with iodine uptake), serious malformations and heart disease.
4.4.3 Agricultural Practices that minimize use of fertilizers
There is proper land management such as ploughing just before the next crop and crop rotation. There is alternative agriculture as in hydroponics. There is gene transfer in plant breeding to have plants with improved qualities such as resistance to insects. Finally, there is the need to educate the public like increasing public awareness of the good agricultural practices the minimize the use of fertilizers.
