Factors of Ecosystem [Part 1]

Every living organism is surrounded by materials and forces which constitutes its environment and from which it must derive its needs. Any external force, substance or condition which surrounds and affects the life of an organism in any way is referred to as environmental factor or ecological factor. These factors are living as well as non-living. The living factor is called the biotic factor and non-living is called the abiotic factor. Thus, the ecosystem is governed by two environmental factors (components) biotic factors and abiotic factors. These factors determine the quality and the viability of the ecosystem.

A) Climatic Factors:
1) Light: The radiant energy coming from the sun in the form of visible spectrum is called Light. Light is one of the most important ecological factors for organisms. It directly or indirectly affects almost all aspects of living organisms.
a) Effects of light on Plants: Light is well known for its effects in photosynthesis, chlorophyll formation, stomata movement, transpiration, tissue formation, growth and development of flowers, seeds and fruits, enzyme and hormone formation. It also plays an important role in the species composition and development of vegetation. The plants grow in strong light or which receive direct sunlight are called heliophytes or sun plants. Whereas the plants growing in diffused or lower intensities of light are termed as sciophytes, photophobic or shade plants.
Photosynthesis: The green plants synthesize their food only in the presence of sunlight by photosynthesis. Light provides energy for this process.
Chlorophyll Formation: Light is essential for the chlorophyll formation. It has marked effect on the number and position of chloroplasts.
Stomata movement: Usually the stomata remain opened in the light and closed in the dark.

Duration of light (photoperiod) plays an important role in flowering of wide varieties of plants. According to the duration of light required by plants for flowering, the plants are classified into following types:
i) Long day Plants: Plant that require long duration of light from the critical day length for flowering is called the long day plant. They mostly flower in summer, e.g. radish, potato, Allium cepa, Hordeum valgare, wheat etc.
ii) Short day plant: Plant that requires short duration of light for flowering from the critical day length is called the short day plant. They mostly flower in winter, e.g. tobacco, Cannabis sativa, Zea mays, Oryza sativa, etc.
iii) Day neutral plant: Plants which show little response to length of daylight are called the day neutral plants, e.g. cotton, balsam, tomato, etc.

b) Effect of Light on Animals: Light shows various effects on animal's life. It affects the growth, colouration of body, migration, reproduction in various insects, birds, fishes, reptiles and mammals. Many nocturnal animals prefer to live in dark while others like hydroids fail to survive in the abscence of light. Light influences the development of the visual organs like 'eyespots' in protozoa; flat ocelli in jellyfish, pit eyes in gastropods, vesicular eyes as in polychaetes, molluscas and some vertebrates, compound eyes in insects and simple eyes or ocelli in other anthropods (Tobias, 1976).

c) Effect of Light on Animal Movement: Lower animals show movement in response to light. For example: Euglena, Ranatra etc. show positive response to light and move towards the source of light, while planarians, earthworms, slugs, siphonophores move away from the source of light. Oriented locomotary movements towards and away from a source of light is called phototaxis.

2) Temperature:

The temperature is the degree of hotness and coldness. Temperature is one of the most essential factors which affects the various vital activities such as the metabolism,behaviour, reproduction, embryonic development, growth and distribution of plants and animals.

a) Metabolic Process: Temperature regulates most of the metabolic activities of microbes, plants and animals. Increase in temperature upto a certain limit, brings about increased enzymatic activity, which increases the rate of metabolism. But an increase in temperature beyond 40 centigrade shows adverse effect on the metabolic rate. High temperature increases transpiration, respiration and causes denaturation of enzymes in plants. The rate of respiration in plants, however, increases with the rise of temperature, but beyond the optimum limit high temperature decreases the respiration rate. The rate of respiration become doubles (like in animals) at the increase of 10 centigrade above the optimum temperature (Vant Hoff's law). A very high temperature (above 50 centigrade) coagulates the protoplast. Low temperature increases the rate of transpiration and retards the rate of absorption, thus the tissues are dehydrated and injured.

b) Effect on growth and development: Both extremely low and high temperature show adverse affect on the growth of plants. A very low temperature below 0 centigrade causes cold injuries such as desiccation, chilling and freezing injury. In desiccation, tissues are dehydrated and injured due to rapid transpiration and slow absorption during winter.

3) Precipitation (Rain fall): Rainfall is the chief source of water. It influences all the vital processes of the living organisms. The water of atmosphere reaches to the earth's surface by rain and again it reaches to the atmosphere through evaporation and transpiration. Thus, a continous circulation of water from earth to atmosphere and vice-versa is called water-cycle. The amount of annual rainfall gratly influencesthe vegetation as well as animal population of a particular region. It is the medium of solutes, raw material in photosynthesis and is essential for maintenance of turgidity of cells. Human beings, animals, birds and plants are closely related with water for their survival. Rainfall distribution in different seasons of the year also may further be important in regional distribution of vegetation. Annual rainfall determines the type of vegetation in any region. For example, rainfall throughout the year produces tropical evergreen forests, good rainfall in one or two seasons causes deciduoud forests. Moderate rainfall in 1 or 2 seasons causes grasslands, while low seasonal rainfall gives rise to deserts. Based on water relationship, plants are classified into three types: Hydrophytes, plants growing in plaent of water; Mesophytes, plants growing on land surface with moderate water supply; Xerophytes, plants growing in scarcity of water.

4) Humidity of Air (Moisture): The water vapour present in the atmosphere is known as humidity. The atmospheric humidity influences directly the form and structure of the plants. It directly influences the physiological process of the plants such as transpiration, absorption of water etc. High percentage of humidity increases the rate of transpiration and absorption. Some plants like lichens, mosses, orchids etc. get their water supply directly from the air. In fungi and other microbes, it plays an important role in germination of spores and subsequent stages in life cycle.

5) Wind: Movement of air from high pressure area to ow pressure area is called the wind. It is an important ecological factor in open areas like plains, sea coasts and at high altitudes like in mountains. It directly affects the rate of transpiration, causes various types of mechanical injuries and dispersal of pollen grains, fruits and seeds. Wind causes a number of physical, and physiological effects on plants, some of which are as follows:

Physical Effects:

a) Breakage and uprooting: High velocity of wind causes premature shedding of flowers, buds and frutis. Sometimes it causes breakage of branches, bending of crops is called lodging. The wind of a very hish velocity sometimes causes complete uprooting of trees.

b) Constant undirectional wind in open areas (sea shores and high mountain tops) causes branches only in wind ward direction. The type of tree is called the flag tree.

Desiccation: Strong wind increases the rate of transpiration by removing saturated air from transpiring areas. Under such condition, plants fail to maintain an internal balance and thus suffer from desiccation.

Dwarfing: Plants growing under the influence of dry winds generally suffer from dehydration which causes loss of turgidity. The plant organs decome dwarfed under such conditions.

Pressure: Pressure caused by air in atmosphere is called atmospheric pressure. The atmospheric pressure has great role in weather and climate and thus acts as directly limiting factor to organisms. Pressure on terrestrial animals affects certain behaviour and metabolism. In the ocean, hydrostatic pressure is important being of tremendous gradient from the surface to the depths. It has a constant effect on aquatic organisms. Generally, great pressures which are found in the depths of the ocean exert a depressing effect.

Fire: Destruction of forests by fires is one of the serious problems observed in dry deciduous forests and grasslands. Frequent annual fires may decrease the growth of grass, herbs and shurbs. However, growth of some plant like Cynodon, Populus, Epilobium, etc. are stimulated by fire. Fire is ocasionally caused by natural phenomenon such as lightning or volcanic activity and mostly by human activities.

Gases: The concentration of gases present in air such as carbon dioxide (0.03%) and oxygen (21%) greatly influence the life of organisms.

a) Carbondioxide: Co2 is mainly used by green plants as raw material in photosynthesis. It is produced by biological respiration and combustion. Increase in concentration of CO2 speed up photosynthesis to a certain level. High CO2 concentration may cause toxic effect in animals including humans. Fishes are affected by high concentration of CO2 and die if water is highly charged with unbound CO2.

b) Oxygen: Oxygen is the product of photosynthesis of green plants (producers). The concentration of oxygen becomes limiting factor for organisms which perform aerobic respiration. It acts as limiting factor in the distribution od animals in aquatic media and at high altitudes of mountains.

pH (Hydrogen ion concentration): It is the relative acidity or alkalinity of the media. A pH below 7 indicates an acid medium; one above 7 indicates an alkaline medium; while the pH value of neutral soil is 7. The growth and productivity of many species are critically related to soil acidity. Some organisms require acidic conditions, others need alkaline conditions while others need neutral conditions of soil and water. Thus, acidity or alkalinity of the media greatly influence the distribution of organisms and become limiting factor.

B) Edaphic Factor (Soil Factor):

Soil is the upper weathered surface of the earth mixed with organic matter and in which micro-organisms live and plants grow. Soil is one of the most important ecological factors which provide nutrition, water supply and anchorage to the plant. The important soil components which affect the vegetation or plant life are as follows:

1) Soil Particles: Depending upon the size of soil particles the international society of soil science has given different names to soil particles, which are as follows:

Clay: diameter less than 0.002 mm

Silt: diameter 0.002 to 0.02 mm

Fine sand: 0.02 to 0.2 mm

Coarde sand: 0.2 to 2.0 mm

Stones and gravel: Above 2.0 mm

2) Soil Texture: On the basis of the proporiton of different sized particles, soils are classified into different textural groups. Soil texture directly influences soil-water, aeration and root penetration. From the above proportion of soil particles it is clear that the loam soil is better for plant growth, because, it contains appropriate proportin of air, sufficient nutritive salts and good water holding capacity. Sandy soils are nutrient-deficient due to high porosity. While silt soils have greater water holding capacity, they are poorly aerated.

3) Soil Air: The spaces between mineral particles contain gases in addition to liquids, which make the atmosphere of soil. Soil air contains slightly lower proportion of oxygen and higher percentage of CO2 in comparison with atmospheric air. Waterlogged soil contains even low percentage of oxygen. Usually, plenty of oxygen in the soil is necessaru for the life of micro-organisms and in the respiration of underground parts of higher plants. It is also essential for seed germionation, because the germinating seeds respire rapidly.

4) Soil Water: Main source of soil water is rainfall. Water in soil is generally present in five forms: (i) Hygroscopic water (ii) Capillary water (iii) Gravitational water (iv)combined water and (v) water vapour. Only the capillary water present in soil is available to the plants. Waterlogged soil excludes soil air and thus it is injurious for plant growth. Low water content in the soil is also injurious for the growth of plant, because it causes wilting of plants. Soil water fulfil the water requirements of plants and it also acts as media by which essential mineral salts enter the plant body.

5) Soil Temperature: Soil temperature gratly influences the plants life. THe absorption rate of water and minerals are reduced by low temperature. Low temperature also causes root injury mostly in winter season in sandy soil. Similarly, a very high temperature is also injurious for root.

6) Soil Organic Matter: Organic matter or soil humus is formed from the death and decay of plants or the parts of plants and animals. Organic matter makes the soil porous and increases the aeration of soil. It also increases the water holding capacity of soil.

7) Soil Reactions: Depending upon the presence of basic and acidic ions, the soil may show acidic, alkaline or neutral reactins. the groeth and productivity of many species of plants are critically related to soil acidity. Species of Rhododendron and Rumex are acid loving and grow best in highly acidic soil. SLightly acidic soils favour the growth of most field crops such as barley, maize, soyabeans, tomato, rye, potato, etc. Slightly alkaline soils favour the growth of ferns and beech trees. The accumulation of calcium, sodium amd magnesium salts increases the alkalinity of soil. The alkaline reaction of soil influences the absorption of water and mineral salts. The acidic or alkaline property of the soil can be measured by pH value.

8) Soil Organisms: It includes both flora and fauna of soil (bacteria, fungi, actinomycetes, algae, blue-green algae, protozoans, rotifers, nematodes, earthworms, molluscas, arthropods etc.) which make the 'biological system' of soil complex. The plants, animals and microbes show marked effects of the soil fertility. Bacteria, fungi and many others are responsible for return of essential elements back to the soil by decomposition of dead organic matter. Earthworms increase the fertility of the soil by adding excretory matters to it and also by making it loose.