This involves the understanding of a whole network of relationships comprising the various exchanges and interactions between the living and non-living. The various structural components of an ecosystem are classified under two main groups, viz., (i) Abiotic or Non-living; and (ii) Biotic or living.
The abiotic component of ecosystem consists of kinds, quantity and distribution of physical and chemical factors such as light, temperature, water, oxygen, carbon, nitrogen, and minerals. The biotic component comprises the kinds, numbers and distribution of living organisms.
Abiotic Factors of Ecosystem
Even in the present age of advanced science, all the abiotic factors of the ecosystem are not known and implications of many have not been understood. The ability of various organisms to utilize or tolerate different abiotic factors vary considerably and it may limit their number, distribution, behavior and relationship with other organisms. The factors that are limiting the living organisms are as follows:
Temperature : Life exists only within a range of 300 degree Centigrade, i.e., from -200 C to 100 C. Actually, most species and their activities are restricted to even a narrower band of temperature. Temperature is often responsible for zonation and stratification occurring, both in water and land environment.
Fresh water has maximum density at 4 degree Centigrade. During winter, upper water surface freezes which prevents the cooling of water below it. In summer with rise of atmospheric temperature, upper surface of pond water becomes warm while lower surface remains cool and is called Epilimnion and Hypolimnion respectively. Between these two, an intermediate zone of varying temperature is called Therrnocline.
Temperature tolerance: The organisms which can tolerate a wide range of temperature are called Eurythermal, while those having very narrow temperature tolerance are called Stenothermal. The temperature at which the activity of the organism is at maximum is the optimum temperature for that organism or groups of organisms. The range of temperature tends to be less in water than on land. Hence, aquatic organisms generally have limited tolerance to change in temperature than animals living in land. However, animals and plants have developed certain specialized structures by which they counter harmful effect of temperature extremes.
Meeting temperature extremes:
(i) Hibernation is the process by which the cold blooded animals become dormant during winter season. The cold blooded animals are called Piokilotherms. During the period of hibernation, the basic metabolic activity rates fall considerably for these animals; and the body temperature comes down. Respiration becomes very negligible and the heart beat lowers very much. With rise in temperature, animals come out of winter sleep and become active.
(ii) Aestivation: It is the period of dormancy during summer and found in certain insects, some invertebrates and mammals. A special method of dormancy, Diapause, during which morphological growth and development are suspended, takes place in insects.
(iii) Homiothermy (Warm Bloodedness): In the case of warm blooded animals, constant body temperature is maintained irrespective of environmental conditions. They remain active throughout the year. This is the case with birds and mammals.
(iv) Thermal Migration: Certain animals and birds avoid adverse temperatures by migrating from one place to another.
(v) Cyclomorphosis: This is a phenomenon in which certain planktonic animals change their body form with change in temperature.
So, temperature has various effects on every aspect of organic life. Metabolic activity, growth and development, distribution, reproductive behaviors, reproduction, sex-ratio and even structure are affected by temperature. In plants, formation of Spores, Cysts are mechanisms by which the seeds are protected in changing temperatures. This is Nature’s gift for the perpetuation of the species.
Everyone knows that water is essential for life and activities of life. From the ecological point of view, water is a limiting factor either in the land environment or in water environment. It is the availability of water that decides the type of vegetation and the style of living by human beings. Water is the main factor controlling the dispersal and distribution of organisms.
Hydrophytes are aquatic plants inhabiting regions around water or wet soil, Plants that grow in regions of moderate water are called Mesophytes. Cultivated agricultural crops and garden vegetables come under this category. Xerophytes are plants that grow in arid or semi-arid regions where there will be little or no water (Example: Cactus). Apart from availability of water, the salinity of water, i.e., the extent of salt concentration decides the type of life.
Depending on this, the aquatic ecosystem can he divided into three categories, viz., Fresh Water ecosystem, Marine ecosystem and Estuarine ecosystem. Generally water salinity results in the loss of water from the body of organisms by Osmosis.
Animals which can tolerate only a small range of salt concentration are called Stenohaline, and animals which tolerate a wide range of salinity in water are called Eughaline. Generally, animals of estuarine ecosystem are euryhaline. On the other hand, animals living in land always face water problems. This would make them conserve water, whenever there are scarcities of water due to seasonal changes. The system has endowed these animals with adaptation to conserve water.
Animals of desert change over to nocturnal habits; some animals develop dry and impervious skin and others reduce sweat glands considerably so as to prevent evaporation of water from the body. Birds and reptiles conserve water by changing their excretory product to solid uric acid. Water is considered as a cyclic commodity within the whole ecosystem.
Sun light is very essential for life, as it is the ultimate source of energy. The evolution of the biosphere and also the existence of biosphere in good state are the result of the process involved in taming of incoming solar radiation in such a way that the useful components of solar radiation are exploited, while harmful components are shielded out. The characteristic behavior of various organisms on the biosphere are much concerned with this process for continuance of the same to perpetuate healthy organic life and they respond well for this process.
Thus, light is not only a vital factor, but also a limiting factor, both at maximum and minimum levels. Ecologically, the quality of light, (i.e., wave length and color) intensity and duration of light etc., are considered to be very important.
Plants and animals respond to different wave lengths of light. Light has a very dominant role to play in the environment on animals and plants. It is essential for photosynthesis in plants. Within optimum limit, photosynthesis will increase in proportion to the intensity of the light.
Aestivation and hibernation of cold blooded animals depend on the extent of solar radiation, i.e., intensity of light. Further, in animals, light initiates the breeding activity by stimulating their gonads. The response of an organism to duration of day-light is called Photoperiodism. This is very important from ecological point of view, as the reproductive behavior of plants and animals is triggered by the sun-light.
Classification of Plants based on photoperiods
On the basis of photoperiod, plants could he classified as (a) Long Day Plants; (b) Short Day Plants; and (c) Day Neutral Plants. Long Day Plants bloom on increased period of day-light; that is 12 hours or more. Short Day Plants bloom and form seed when day-light period is less than 12 hours. Blooming of Day Neutral Plants is not affected by the length of day-light.
In animals, the effect of photoperiod is manifold. It increases the reproductive activity, storing of food and migrating to places of warmth and security. The intensity of light changes the color of skin by changing the pigment in it and it also reacts on the development of the eyes of animals and their efficiency. For the animals in the depth of ocean, the size of eyes increases, as the intensity of light decreases.
In lightless zones, the size and efficiency of eyes decrease. In certain lower order animals, the locomotion (movement) is influenced by light. This phenomenon is called Photokinesis. When only a part of an organism moves in response to sunlight, the phenomenon is called Phototropism which is quite common in plants. The branches and creepers move towards sun-light.
Air and Humidity :
Air currents and humidity also regulate the life of organisms. Winds determine the rate of transpiration and the velocity of the wind determines the survival of the plants. Winds help in the dispersal of seeds and fruits. Humidity in atmosphere regulates the water evaporation from the body of animals and surface of the land and also in plants. This process is done by means of transpiration, perspiration and other means. Plants and animals show various adaptations to withstand dry conditions to certain extent.
Topography and Soil :
The Topography tells about surface features of the earth, whether it is a plain land or mountain or valley or plateau, etc. Topography, besides making geographical separation, influence the type of animals and plants. Height of mountains, steepness of slopes, the extent of valleys and basins on land influence the flora and fauna of the regions.
The factors related to the soil influence a lot on the type of vegetation and animals The soil texture, porosity of the soil, chemicals and their concentration in the soil, percentage of oxygen, etc., determine a particular type of vegetation and animal form. It is the soil which supports a comply` group of animals, vegetation, bacteria, worms, insects, protozoans, nematodes and numerous vertebrates.
Biotic Factors of Ecosystem
The biotic components of the ecosystem can be grouped as (1) Producers (2) Consumers and (3) Decomposers. The relationships between these components of the ecosystem are not only unique, but also mutual for the preservation of the biosphere in perfect order.
(1) Producers : In the biosphere only green plants and a few organisms live by taking energy directly from the non-living things of the environment. Not only this, they convert the form of energy and make it available to all other organisms to live. In this respect, these organisms and green plants are called Producers as they produce the chemical energy required by other organisms for their sustenance.
Green plants which are chlorophyll-bearing, assimilate carbon dioxide into energy rich carbon compounds in the presence of sun-light, releasing oxygen as a byproduct. Thus these green plants produce not only food for other organisms, but also oxygen which is very essential for living. The algae of a pond, the trees of the forest are very essential for producing food for eating and oxygen for breathing.
In a pond ecosystem, the producer organisms include Phytoplankton which are minute floating plants. When in abundance, these give a greenish color to the ecosystem such as lakes, ocean, etc. In this category falls filamentous algae which occur floating in water. The plants which are rooted and floating on the surface of water fall under the second category comes . In the third category comes plants which are submerged in water with or without roots. In the fresh water pond ecosystem, we can find many of these types of plants like lotus, lily and eichornia (water-hyacinth).
(2) Consumers: Consumers in the ecosystem are those organisms which obtain their energy form plants, either directly or indirectly. These organisms cannot find sources of energy within and they have to depend on the energy-food produced by plants. All animals live only at the expense of green plants. A community without green plants cannot exist, whereas a community without animals can. Among consumers, we have Primary Consumers and Secondary Consumers.
Animals that live directly on the green plants are primary consumers and they are called herbivore, Animals which eat herbivorous animals are called carnivorous and these animals come under the category of secondary consumers, as their food consists of primary consumers. Sonic, ecosystems contain Tertiary Consumers also, i.e., carnivores that feed on other carnivores. Omnivores are those consumers that derive their energy both from producers and herbivores.
(3) Decomposers: When all organisms, both producers and consumers die after completing their life cycle, they become food for bacteria and mould. These organisms, i.e., bacteria are called decomposers and they operate in relay terms, simplifying step by step the organic constituents of each dead body. They release material which is cycled back to the soil and atmosphere. In this process, the bacteria obtain energy and chemical substances for their own growth and reproduction.
Therefore, the decomposers play an important role in the ecosystem by releasing the vital materials from dead organisms. The decomposers comprise a very wide and diverse group of organisms which act at different levels in the process of decay of dead animals. The final group of decomposers release energy. The decomposers in the fresh water ecosystem are called Saprophytes found at the bottom of the ponds. When temperature and other conditions are favorable, the decomposition is very rapid.