In this essay we will discuss about the six main climatic factors that influence environment.
Essay # 1. Atmospheric Gases:
The gases present in the atmosphere are chiefly oxygen, carbon dioxide and nitrogen which greatly influence the living organisms.
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Atmosphere is the thick gaseous envelope around the earth.
The composition of atmospheric air is:
(1) Oxygen = 20.84%
(3) Nitrogen = 78.64%
(2) Carbon dioxide = 0.03%
(4) Water vapours = 0.1%
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Beside these gaes, dust particles, smoke (industrial discharge), micro-organisms, pollen grains, organic gases (e.g. methane released during the decomposition of dead plants and animals) and other gases (SO2, SO3, NH3, etc. released from industries and volcanoes) are also present. These contents greatly affect the weather and living organisms.
(i) Oxygen:
Main sources of oxygen are producers which evolve oxygen as a by-product of photosynthesis. It forms 20.84% of the atmospheric air and is chiefly used by most of living organisms in their aerobic respiration except certain anaerobes e.g. Entamoeba, Taenia, Ascaris, Fasciola and many bacteria like Clostridium.
These organisms are adapted to live in oxygen-free habitats through anaerobic respiration. Entamoeba can survive even in the presence of small amount of oxygen so is a microaerobe. Oxygen acts as a limiting factor in the distribution of animals in aquatic media and at high altitudes of mountains (e.g. Andes lake) due to low atmospheric oxygen.
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So animal life, with certain exceptions, is wanting in fresh-water bodies polluted with industrial wastes causing low oxygen tension and deep sea waters (e.g. Black sea). Animals which can survive even in highly polluted water include Colpidium, Paramecium, blood worm and sludge worm. It is so as the water (about 800 times denser than air) contains much less free oxygen than air (only about 1/30 of the oxygen present in equal volume of air).
So aquatic animals especially fishes are nicely adapted to counter current mechanism (for rapid oxygen uptake) and rapid circulation of water over the respiratory surface of the gills by a continuous one way flow.
(ii) Carbon Dioxide:
Main sources of CO2 are animals (release CO2 in expired air), decomposers and combustion processes going on in the industries and automobiles. CO2 forms about 0.03 per cent by volume. It is mainly used by the producers as a raw material in the process of photosynthesis. So is essential both for plants and animals.
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About 50% of the CO2 is used by oceans and green plants. Atmospheric CO2 is always a limiting factor for photosynthesis. So photosynthesis increases in CO2 upto 15 to 20 times. However, the amount of CO2 in the water is usually not a limiting factor for land animals.
(iii) Nitrogen:
It forms about 78.64 per cent by volume in the atmosphere. It is chemically inert gas but can be used to form nitrites and nitrates under electric discharges (non-biological) or by nitrogen fixing bacterium e.g. Rhizobium, and cyanobacteria e.g. Nostoc, Anabaena, etc. (called biological N2-fixation).
Essay # 2. Light (Radiation Factor):
Light is a very important of the climatic factors:
Which is directly responsible for the growth, development and differentiation of plants? Similarly, light, as a complex physical factor, also affects the colour vision, eye-size, skin pigmentation, migration, reproduction and biological periodicity of the animals. Thus, light is a factor of physical and physiological importance.
Parameters of light affecting the living organisms:
The activities of both plants and animals depend upon three parameters of light—light intensity, light quality and light duration.
Light intensity of the atmosphere depends upon a number of factors like season, altitude, latitude and atmospheric conditions. Atmospheric components like gases (N2, O2 and CO2 etc.) and suspended particles (clouds, smoke, dust etc.) reduce light intensity. According to Geiger out of morning solar radiations, 42% are reflected (33% by clouds and 9% by dust particles), 10% are absorbed by the ozone layer and only 48% reaches the surface of the earth. The intensity of light is further reduced by additional vegetational cover. It is also greatly affected by the topography of the habitat e.g. greater on south-facing slopes of the mountains.
Light quality is also modified by several environmental factors e.g. water vapours absorb the longer wavelengths particularly infra-red while reflect the green and blue wavelengths of light.
Daily light duration varies with the tilt of earth’s axis. On the equator, the length of day is almost 12 hours while it varies with season in temperate area. The days grow longer as spring progresses and June 22 is longest day, while December 21 is shortest day. The day length is 24 hours at the poles throughout the summer.
Essay # 3. Thermal Factor (Temperature):
Temperature is the degree of hotness or coldness of a substance. It is the most important ecological factor affecting almost all the metabolic activities of the organism. Every physiological function has an optimum temperature at which it shows the maximum metabolic rate. The vertical temperature gradient over earth’s surface is called lapse rate. This value comes equal to 65°C per 1000 m elevation.
Change in temperature is affected by factors like latitude altitude, topography, vegetation and slope. Temperature shows a great amount of variation altitudinally and latitudinally. The mean temperature of air changes by 10° F with every latitude. Obviously, the temperature values are maximum at the equator and decrease gradually towards the poles. Similarly, it also decreases from plains to mountain tops.
It ranges from subzero levels in polar areas and high altitudes to >50°C in tropical deserts in summer. Most of the organisms can survive in the temperature range of 0- 60°C except certain bacteria, cyanobacteria, shelled protozoans, dry seeds, certain yeasts etc.
The bacteria and cyanobacteria are known to survive even in thermal spring (60-90°C) or permafrost (-30° to -50°C). But most of the organisms are killed by higher temperatures due to denaturation of enzymes while others are killed by very low temperature due to freezing of body fluids except dry seeds, spores and cysts which have no water. Tolerance power to the extremes of temperature varies from species to species.
Thermal Stratification in Lakes:
In deep aquatic systems, due to differences in temperature of water at varying depths leads to thermal stratification (Fig. 13.8). A zone of slow change in temperature is called thermocline. During summer, surface water bears a higher temperature, which is separated from deep water by thermocline. Two layers are distinguishable due to thermocline.
(i) Epilimnion:
It represents upper layer of water. In temperate lakes, water is at freezing temperature on surface, in winter season. This water is cool in autumn and warm in spring. This leads to free mixing of water in aquatic system and is called as spring turn over. This leads to redistribution of oxygen and nutrients leading to excessive growth of phytoplankton.
(ii) Hypolimnion:
It represents the lower layer of water body and temperature is about 4°C during winter in temperate lakes.
Due to stratified condition in summer and winter, growth of phytoplanktons is highly regulated due to less supply of oxygen and nutrients.
Temperature Based Zonation:
a. Latitudinal Zones (Fig. 13.9):
As many as six temperature-based terrestrial latitudinal zones are differentiated north of equator, each being characterized by a specific vegetation type e.g. Snow, tundra, coniferous forests, deciduous forests, grasslands or deserts and tropical rainforests.
b. Altitudinal Zones:
As many as four temperature based terrestrial altitudinal zones are differentiated in Himalayas, each having specific vegetation type: alpine (having Rhodendron, Juniperus), temperate (mainly conifers, oaks and Magnolia), tropical and subtropical zones (having mixed forests, bamboos, sal, etc.)
Adaptation of Plants to Extremes of Temperature:
In order to survive under extremes of temperature, plants have evolved many morphological and physiological adaptations. These are found in xerophytes. Mesophytes and hydrophytes lack adaptation.
Leaves in many plants are vertically oriented to avoid their perpendicular exposure to incoming light. Leaf- colouration in many desert plants are of adaptive significance. Whitish or grey green leaf colouration escape extreme heat absorption. Thick cuticle, leaf hairs etc. also help in reflecting the heat and saving the underlying tissues from injury. Transpiration reduces the temperature of leaf by utilizing heat in the evaporation of water.
Low degree of protoplast hydration increases heat tolerance as can best be seen in lichens. Many plants escape thermal extremes by producing spores or seeds that are capable to withstand the extremes of temperatures. In some plants, the above ground vegetative parts are destroyed by extreme temperature but the plant survive by means of underground tubers, stolons, corms, rhizomes etc. In some plants, there is an increase in osmotic concentration that prevent freezing under low temperatures.
The amount of annual rainfall greatly affects the vegetation as well as animal population of a particular region e.g:
1. Tropical areas, having heavy rainfall throughout the year so with high relative humidity, are with evergreen forests and abundant faima.
2. In areas with heavy rainfall during winter and low rainfall during summer, are with sclerophyllous forests.
3. The areas with heavy rainfall during summer and low during winter are characterized by the grasslands.
4. The areas with scanty rainfall have deserts with xerophytic vegetation.
The overall influence of precipitation on the distribution of plants has been expressed by Schimper’s third law which states that “the type of vegetation in tropical and sub-tropical region is controlled by the total amount and seasonal distribution of rainfall and humidity of air.” This change in vegetation greatly affects the distribution of animals so different geographical areas have different types of animals.
Essay # 4. Wind:
Air in motion is called wind. Speed of wind is called wind velocity.
It affects both plants and animals in following ways:
1. Strong winds cause soil erosion so reducing soil fertility. These also cause desertification by shifting of sand particles to fertile areas.
2. These cause lodging (flattening of plants against the ground) of plants like wheat, rice, maize, oat, sugarcane etc.
3. These increase the rates of evaporation and transpiration leading to desiccation which cause dwarfism in the plants which generally take cushion form.
4. These help in pollination in the anemophillous gymosperms (e.g. Pinus) and angiospermic plants (e.g. Cannabis).
5. Wind helps in dispersal of many seeds, fruits, cysts, spores, eggs and even some adult animals like winged insects, ballooning spiders etc. The animals may appear even in those areas where these were earlier absent. Dispersal of seeds and fruits by air is called anemochory. Plants have special structures for anemochory e.g. winged seeds in Pinus, coma in seeds of Calotropis, persistent hairy style with the fruits of Clematis, Pappus with the fruit of Tragobogon, etc.
6. Unidirectional winds stimulate the development of flag trees (with branches directed on one side only (Fig. 13.11) on hill tops and sea shore, while many trees {e.g. Pinus flexilis) become inclined.
7. These also help in migration of flying animals.
8. Plants may develop eccentric secondary growth leading to anatomical deformities e.g. a reddish coloured xylem called reaction or compression wood on the compressed side.
9. Salt sprays. Wind, moving from sea to land, carries thin film of salt which is sprayed on the coast vegetation. The plants resistant to this hyper-salinity shall survive while many plants die due to desiccation by exosmosis.
The effect of wind on plants is both direct and indirect. The direct effect is usually mechanical represented by breaking off the branches and twigs and uprooting of the plant. The action of wind can be seen at timber line (above 3600 meter altitude), where the growth of plants become stunted and twisted. The indirect effect of winds is physiological. Due to strong winds, there is excessive transpiration which increases desiccation of the plant body. Loss of turgidity during maturation and expansion of cells result in dwarfing.
In addition to above effects, wind pose some useful effects on the plants. It replaces the old air with fresh air, thus’, helping in gaseous, exchange. Slow wind helps in pollination in many plants (wind-pollinated plants) and also serves an agent for fruit and seed dispersal.
Essay # 5. Atmospheric Humidity:
It is the amount of water vapours present in the atmosphere. Relative humidity (RH) is the amount of moisture present in the air as the percentage of the amount of water which the air can hold at saturation at the given temperature. It is affected by light intensity (decreases with increase in relative humidity), temperature (water holding capacity of air doubles with every 10°C rise in temperature), wind velocity, vegetation and soil water.
It plays an important role in life of plants as well as animals:
1. It promotes the growth of hygroscopic roots in epiphytes e.g. orchids. Such plants growing in high R.H. are called hygrophytes e.g. lichens.
2. It regulates the evaporation of water from the body of land organisms in transpiration and perspiration.
3. It promotes the germination of spores in fungi.
4. Low R.H. promotes the development of spines, hair, thorns, succulent leaves or stems, thick cuticle, sunken stomata, increased succulency, etc. in desert plants.
5. High R.H. causes poor development of vascular and mechanical tissue, and palisade tissue, so the plants are elongated, thinner and paler.
6. Similarly, certain animals are restricted in areas with high humidity e.g. in tropical rain forests, while some are found in areas with low humidity e.g. in deserts. Many animals occur in areas with intermediate humidity.
In relation to humidity, several plants produce morphological and anatomical changes. For example, development of hygroscopic roots in orchids because they live under humid conditions, and development of spines, hairs, thorns, succulent leaves or stems in desert plants, where relative humidity is low. Similarly, thick cuticle, sunken stomata, more water storage tissue, mucilage secretion, more scleranchyma are other features of plants found in arid regions i.e. low humidity.
Under humid conditions the plants are elongated, thinner and pale. Their leaves become small, transparent and thin due to the poor development of pallisade tissue. In moist conditions, there is an enlargement of intercellular space, poor development of vascular and mechanical tissue.
Essay # 6. Water:
Water is second most important ecological factor after the temperature. Water is essential for life. Even the origin of life occurred in water on primitive earth. It covers more than 70% of the earth’s surface. The chief source of soil water is atmospheric precipitation. It may occur in the form of snow, rain, hail, sleet, frost, dew, fog or mist.
About 45% of water flows into rivers, 20% percolates into soil and 35% lost by evaporation. Melting of snow and ice are also important sources of water. Land plants derive water from the soil while the land animals derive water from pools, ponds, lakes, rivers, springs etc. The organisms have to face different problems of water scarcity or abundance, so osmoregulation is required for their proper functioning.
Effect of Rainfall on Vegetation:
Rainfall is the chief source of water present in the soil. Rainfall is uneven at different places of earth. Cherrapunji gets >11,000 mm rainfall every year when compared with deserts receiving <100 mm year each year.
Precipitation is an indirect factor affecting plants through atmospheric humidity and water content of the soil. However, the vegetation of a particular region is primarily determined by the amount and seasonal distribution of rainfall. Not only the distribution but even the productivity of plants is heavily dependent upon water. In a broad sense, depending upon the amount of rainfall, the vegetation may be of three types- forests, grasslands and deserts.
i. Where the rainfall is evenly distributed throughout the year, the plants show luxuriant growth as found in tropical, subtropical and warm-temperate rain forests.
ii. Where rainfall does not occur in winter, the vegetation consists of broad-leaved trees accompanied with leaf fall as in cold temperate deciduous forests.
iii. In cold temperate coniferous forests, the plants have needle-like leaves and remain evergreen. They show xerophytic structure as rainfall is not available throughout the year.
iv. Where water is scarce and there is low temperature, the vegetation comprises of short life-cycled plants. Trees and shrubs are not present here. It can be seen in Tundras and ice deserts.
v. Light rainfall in winter and heavy rain in summer season corresponding to the growing season of plants like grasses, herbs, sometimes shrubs and scattered trees are the characteristic of grasslands.
vi. Scanty rainfall and scanty vegetation of scattered thorny shrubs and trees correspond to deserts.