Ecology
- The interactions of a particular group of organisms with abiotic factors within a particular habitat resulting in clearly defined energy flows and material cycles on land, water and air, are called ecological systems.
- The term ecology is derived from the Greek word 'oikos' meaning 'house', combined with the word 'logy' meaning the 'science of or 'the study of.
- Literally, ecology is the study of the earth as a 'household', of plants, human beings, animals and micro-organisms.
- They all live together as interdependent components.
- A German zoologist Ernst Haeckel, who used the term as 'oekologie' in 1869, became the first person to use the term 'ecology'.
- The study of interactions between life forms (biotic) and the physical environment (abiotic) is the science of ecology.
- Hence, ecology can be defined as a scientific study of the interactions of organisms with their physical environment and with each other.
- A habitat in the ecological sense is the totality of the physical and chemical factors that constitute the general environment.
- A system consisting of biotic and abiotic components is known as ecosystem.'
Types of Ecosystems
- Ecosystems are of two major types: terrestrial and aquatic.
- Terrestrial ecosystem can be further be classified into 'biomes'.
- A biome is a plant and animal community that covers a large geographical area.
- The boundaries of different biomes on land are determined mainly by climate.
- Therefore, a biome can be defined as the total assemblage of plant and animal species interacting within specific conditions.
- These include rainfall, temperature, humidity and soil conditions.
- Some of the major biomes of the world arc : forest, grassland, desert and tundra biomes.
- Aquatic ecosystems can be classed as marine and freshwater ecosystems.
- Marine ecosystem includes the oceans, estuaries and coral reefs. Freshwater ecosystem includes lakes, ponds, streams, marshes and bogs.
Structure and Functions of Ecosystems
- From a structural point of view, all ecosystems consist of abiotic and biotic factors.
- Abiotic factors include rainfall, temperature, sunlight, atmospheric humidity, soil conditions, inorganic substances (carbon dioxide, water, nitrogen, calcium, phosphorus, potassium, etc.).
- Biotic factors include the producers, the consumers (primary, secondary, tertiary) and the decomposers.
- The producers include all the green plants, which manufacture their own food through photosynthesis.
- The primary consumers include herbivorous animals like deer, goats, mice and all plant- eating animals.
- The carnivores include all the flesh-eating animals like snakes, tigers and lions.
- Certain carnivores that feed also on carnivores are known as top carnivores like hawks and mongooses.
- Decomposers are those that feed on dead organisms (for example, scavengers like vultures and crows), and further breaking down of the dead matter by other decomposing agents like bacteria and various microorganisms.
- The producers are consumed by the primary consumers whereas the primary consumers are, in turn, being eaten by the secondary consumers.
- Further, the secondary consumers are consumed by the tertiary consumers. The decomposers feed on the dead at each and every level.
- They change them into various substances such as nutrients, organic and inorganic salts essential for soil fertility.
- Organisms of an ecosystem are linked together through a food chain.
- For example, a plant eating beetle feeding on a paddy stalk is eaten by a frog, which is, in turn, eaten by a snake, which is then consumed by a hawk.
- This sequence of eating and being eaten and the resultant transfer of energy from one level to another is known as the food-chain.
- Transfer of energy that occurs during the process of a food chain from one level to another is known as flow of energy.
- However, food-chains are not isolated from one another. For example, a mouse feeding on grain may be eaten by different secondary consumers (carnivores) and these carnivores may be eaten by other different tertiary consumers (top carnivores).
- In such situations, each of the carnivores may consume more than one type of prey. As a result, the food-chains get interlocked with one another.
- This interconnecting network of species is known as food web.
- Generally, two types of food-chains are recognised: grazing food-chain and detritus food- chain.
- In a grazing food-chain, the first level starts with plants as producers and ends with carnivores as consumers at the last level, with the herbivores being at the intermediate level.
- There is a loss of energy at each level which may be through respiration, excretion or decomposition. The levels involved in a food chain range between three to five and energy is lost at each level.
- A detritus food-chain is based on autotrophs energy capture initiated by grazing animals and involves the decomposition or breaking down of organic wastes and dead matter derived from the grazing food-chain.
Figure: Structure and Functions of Ecosystems
Biogeochemical Cycles
- The sun is the basic source of energy on which all life depends.
- This energy initiates life processes in the biosphere through photosynthesis, the main source of food. and energy for green plants.
- During photosynthesis, carbon dioxide is converted into organic compounds and oxygen.
- Out of the total solar insolation that reaches the earth's surface, only a very small fraction (0.1 per cent) is fixed in photosynthesis.
- More than half is used for plant respiration and the remaining part is temporarily stored or is shifted to other portions of the plant.
- Studies have shown that for the last one billion years, the atmosphere and hydrosphere have been composed of approximately the same balance of chemical components.
- This balance of the chemical elements is maintained by a cyclic passage through the tissues of plants and animals.
- The cycle starts by absorbing the chemical elements by the organism and is returned to the air, water and soil through decomposition.
- These cycles are largely energised by solar insolation.
- These cyclic movements of chemical elements of the biosphere between the organism and the environment are referred to as biogeochemical cycles.
- Bio refers to living organisms and geo to rocks, soil, air and water of the earth.
- There are two types of biogeochemical cycles: the gaseous and the sedimentary cycle.
- In the gaseous cycle, the main reservoir of nutrients is the atmosphere and the ocean. In the sedimentary cycle, the main reservoir is the soil and the sedimentary and other rocks of the earth's crust.
The Carbon Cycle
- Carbon is one of the basic elements of all living organisms. It forms the basic constituent of all the organic compounds.
- The biosphere contains over half a million carbon compounds in them.
- The carbon cycle is mainly the conversion of carbon dioxide. This conversion is initiated by the fixation of carbon dioxide from the atmosphere through photosynthesis.
- Such conversion results in the production of carbohydrate, glucose that may be converted to other organic compounds such as sucrose, starch, cellulose, etc.
- Here, some of the carbohydrates are utilised directly by the plant itself.
- During this process, more carbon dioxide is generated and is released through its leaves or roots during the day.
- The remaining carbohydrates not being utilised by the plant become part of the plant tissue.
- Plant tissues are either being eaten by the herbivorous animals or get decomposed by the microorganisms.
- The herbivores convert some of the consumed carbohydrates into carbon dioxide for release into the air through respiration.
- The micro-organisms decompose the remaining carbohydrates after the animal dies.
- The carbohydrates that are decomposed by the micro-organisms then get oxidised into carbon dioxide and are returned to the atmosphere.
The Oxygen Cycle
- Oxygen is the main by-product of photosynthesis.
- It is involved in the oxidation of carbohydrates with the release of energy, carbon dioxide and water. The cycling of oxygen is a highly complex process.
- Oxygen occurs in a number of chemical forms and combinations.
- It combines with nitrogen to form nitrates and with many other minerals and elements to form various oxides such as the iron oxide, aluminium oxide and others.
- Much of oxygen is produced from the decomposition of water molecules by sunlight during photosynthesis and is released in the atmosphere through transpiration and respiration processes of plants.
The Nitrogen Cycle
- Nitrogen is a major constituent of the atmosphere comprising about 79 per cent of the atmospheric gases.
- It is also an essential constituent of different organic compounds such as the amino acids, nucleic acids, proteins, vitamins and pigments.
- Only a few types of organisms like certain species of soil bacteria and blue green algae are capable of utilising it directly in its gaseous form.
- Generally, nitrogen is usable only after it is fixed. 90 per cent of fixed nitrogen is biological.
- The principal source of free nitrogen is the action of soil micro-organisms and associated plant roots on atmospheric nitrogen found in pore spaces of the soil.
- Nitrogen can also be fixed in the atmosphere by lightning and cosmic radiation.
- In the oceans, some marine animals can fix it. After atmospheric nitrogen has been fixed into an available form, green plants can assimilate it.
- Herbivorous animals feeding on plants, in turn, consume some of it.
- Dead plants and animals, excretion of nitrogenous wastes are converted into nitrites by the action of bacteria present in the soil.
- Some bacteria can even convert nitrites into nitrates that can be used again by green plants.
- There are still other types of bacteria capable of converting nitrates into free nitrogen, a process known as denitrification.
Ecological Balance
- Ecological balance is a state of dynamic equilibrium within a community of organisms in a habitat or ecosystem.
- It can happen when the diversity of the living organisms remains relatively stable.
- Gradual changes do take place but that happens only through natural succession.
- It can also be explained as a stable balance in the numbers of each species in an ecosystem.
- This occurs through competition and cooperation between different organisms where population remains stable.
- This balance is brought about by the fact that certain species compete with one another determined by the environment in which they grow.
- This balance is also attained by the fact that some species depend on others for their food and sustenance.
- Such accounts are encountered in vast grasslands where the herbivorous anim&ls (deer, zebras, buffaloes, etc.) are found in plenty.
- On the other hand, the carnivorous animals (tigers, lions, etc.) that are not usually in large numbers, hunt and feed on the herbivores, thereby controlling their population.
- In the plants, any disturbance in the native forests such as clearing the forest for shifting cultivation usually brings about a change in the species distribution.
- This change is due to competition where the secondary forest species such as grasses, bamboos or pines overtakes the native species changing the original forest structure. This is called succession.
- Ecological balance may be disturbed due to the introduction of new species, natural hazards or human causes.
- Human interference has affected the balance of plant communities leading to disturbances in the ecosystems.
- Such disturbances bring about numerous secondary successions.
- Human pressure on the earth's resources has put a heavy toll on the ecosystem.
- This has destroyed its originality and has caused adverse effects to the general environment.
- Ecological imbalances have brought many natural calamities like floods, landslides, diseases, erratic climatic occurrences, etc.
