Meaning of Ecology
The term ecology is derived from two Greek words, oikos means 'home' and logos means 'study of". Literally, the term ecology refers to the study of living organisms at home. As all organisms have their own specific surroundings, the term ecology means the study of living systems in relation to their environment.
Definition
According to Taylor, Ecology is 'the science of all relation of all organisms to all their environments.'
Andrewartha's definition states that Ecology "is the scientific approach to the study of environmental interactions which control the welfare of living things, regulating their distribution, abundance, reproduction and evolution."
Ecosystem
Our environment is enriched with various living and non-living natural resources. Among them, the biotic community undergo a life cycle that starts from birth and ends in death. This life cycle can flourish in an environment which is full of food, nutrients, energy and their continuous flow. Such a system is termed as ecosystem. The living community of plants and animals in any area together with the non-living components of the environment, such as soil, air and water constitute the ecosystem.
Definition of Ecosystem
Ecosystem is defined as 'a complex of living organisms, physical environment and all their interrelationships in a particular unit of space'.
The structure and functions of an ecosystem
The structure indicates compositional aspects of the biotic community and the functions mean the rate of energy flow and nutrient cycles.
Structure of Ecosystem
An ecosystem is composed of two major components.
1. Abiotic (non-living) 2. Biotic (living)
Abiotic Ecosystem
The non-living factors or the physical environment prevailing in an ecosystem form the abiotic component. They include media such as soil, water, land, air, minerals, light, climate etc. The abiotic constituents are further classified into physical and chemical constituents. The physical constituents are soil, temperature, light and water and chemical component constituent inorganic and organic structure such as phosphorous, carbon, hydrogen, nitrogen, carbohydrates, fats, protein etc.
Biotic Ecosystem
The living organisms including plants, animals and microorganisms like bacteria, fungi that are present in an ecosystem form the biotic components.
The biotic components are classified into producers (Autotrophs) and consumers (Heterotrophs). Consumers are further classified into macro consumers and micro consumers. Macro consumers include herbivores,carnivores and omnivores and micro consumer are the decomposers.
On the basis of the role of biotic components in the ecosystem, they can be classified into three groups.
(a) producers, (b) consumers, (c) decomposers or reducers
a. Producers
Producers refer to those organisms which either produce food or convert the compounds from one form to another. For this they obtain energy from sunlight or from the inorganic compounds. The green plants trap energy from sunlight and prepare proteins, carbohydrates and fats using their chlorophyll. This process is known as photosynthesis.
The chemical energy stored by the producers is used partly by the producers for their own growth and survival and the remaining is stored in the plant parts for their future use.
b. Consumers
Consumers refer to those organisms which consume the food produced by the producers and gain the energy for their survival. Though they cannot produce food for themselves, they can transform organic compounds from one form to another.
The consumers are of four types:
(i) Primary consumers (or herbivores) are the animals like goats, deers, cattles, grasshoppers etc. which feed on primary producers.
(ii) Secondary consumers (or small carnivores) are the animals such as lizards, cats, foxes, snakes etc. which feed on primary consumers.
(iii) Tertiary consumers (or large carnivores) are the animals like wolves, hawks etc. which feed on secondary consumers.
(iv) Quarternary consumers (or largest carnivores) are the animals like bears, tigers, lions etc. which feed on tertiary consumers.
c. Decomposers
Decomposers (or micro-consumers) are those organisms which eat dead organism (animals, plants and other living beings), and transform the organic compounds back into inorganic compounds. These inorganic compounds are then used by the 'producers' to prepare food. In this way, there occurs a cyclic exchange of substances between the living community and the environment.
Functions of Ecosystem
An ecosystem performs the following functions.
1. It allows flow of biological energy i.e., controls the rate of production and respiration of the community.
2. It controls the rate of nutrient cycles i.e., production and consumption of minerals.
3. It regulates both ways i.e., the environment by organisms and the organisms by environment. For example, the nitrogen fixing by bacterias is the process of 'environment regulation by organisms', and photoperiodism is the process of 'organisms regulation by environment".
4. It allows circulation of chemical elements along characteristic paths from environment to organisms and back to environment. In this way it provides nutrients to the 'producers' which build-up organic matter.
Energyflow in the ecosystem
Flow of energy is an essential feature of all ecosystems. Ecosystems depend on a steady and continuous supply of energy inorder to maintain structural organisations and to carryout all life preserving activities. It is well known that the sun is the ultimate source of energy. The ecosystem requirement of energy ultimately depends on solar energy. The importance of its uninterrupted flow can be understood by the following examples.
1.If the quantity of solar energy (sunlight) is reduced, the quantity and quality of forest will degrade and the growth will be inadequate.
2.If the quality of solar energy is poor, ie it's intensity is less than normal,plantation and vegetation will be scarce.
Ecological Succession
Ecological succession means ecological development. It refers to the process of gradual change in conditions of environment, and the replacement of older species. Over the time, it undergoes automatically. This is an ever continuing phenomenon that happens by means of autogenic process. The occurrence of ecological succession has the following characteristics.
1. It is a systematic process that involves changes in species structure.
2. The changes are directional and take place as a function of time.
3. The succession occurs due to changes in physical environment and population of the species.
4. The changes also occur due to population explosion of the species.
5. The changes are predictable. The process of succession is self-going. and biologically feasible.
Food Chain
The transfer of food energy from the producers, through a series of organisms (herbivores, to carnivores to decomposers) with repeated eating and being eaten is known as food chain. The various steps in a food chain are called trophic levels. Energy is transferred from one trophic level to another trophic level.
Producers utilise the radiant energy of the sun which is transformed into chemical energy during photosynthesis. Here, green plants occupy the first
trophic (nutritional) level. The energy stored in the food manufactured by the green plants, is then utilised by the herbivores, which constitute the second trophic level. Herbivores, in turn are eaten by the carnivores, which forms the third trophic level. They are called secondary consumers, which in turn are eaten by the tertiary consumers (carnivores). Some organisms are omnivores eating the producers as well as carnivores. Such organisms may occupy more than one trophic level in the food chain.
A food chain in grass land ecosystem starts with grasses and forbs and goes through grass hoppers, the frogs, the snake and the hawk in an orderly sequential arrangement based on the food habits. In a pond, it starts with phytoplanktons and macrophytes, going through water flees, smaller fish, bigger fish, birds, the larger animals and so on.
In all ecosystems two types of food chains are distinguished. They are:
(i) Grazing food chain - It starts from the living green plants, goes to grazing herbivores and on to carnivores. Cattle, grazing on grass land, deer browsing in forests and insects feeding on crops and trees are the important links in this food chain. Some of the grazing food chains are as follows:
Grass Grasshopper→Frog→ Snake → Hawk → Micro-organisms
Paddy → Mouse → Snake → Kite→ Micro-organisms
Grass → Deer → Tiger→ Micro-organisms
(ii) Detritus food chain-It starts with dead organic matter and passes through detritus feeding orgainsims in soil (microbes) and then to organisms feeding on detritus feeders. A large fraction of energy flows through the detritus food chain. The two types of food chains are linked together and belong to the same ecosystem.