Environmental Factors

5 Ecological Factors that Constitute the Environment of an Organism

Some of the major ecological factors that constitute the environment of an organism are as follows: 1. Climatic Factors 2. Edaphic Factors 3. Topographic Factors 4. Biotic Factors 5. Limiting Factors.

In any eco-system, a living organism is influenced by a number of factors and forces. These environmental factors are known as eco- factors or ecological factors which include light, temperature, soil, water etc. These factors may be biotic (living) and abiotic (non­living). The sum total of all these factors constitutes the environ­ment of an organism.

All these ecological factors can be broadly classified into the following divisions:

1.      Climatic or Aerial factors:

a.        Light

Light plays an important role in the species composition and development of vegetation. Light is abundantly received on the surface of the earth. And, on an average approximately only 2-3 per cent of this solar energy is used in Primary Productivity.

Light intensity shows special variations due to the factors like atmos­pheric water layer, particles dispersed in the air, etc. Further, the vegetation of an area may also affect the light intensity. In deep shade under trees, or under water, light becomes limiting below which photo-synthesis is not sufficient for effective growth.

The plants are influenced by light in the following ways: Effect on Chlorophyll synthesis, Photosynthesis, number and Position of Chloroplasts, Respiration, Transpiration, Production of Hormone, development of Flowers, Fruits and Vegetative parts, Formation of Anthocyanin Pigment, Movement, Photoperiodism, Seed Germination, Distribution of Plants, and Effect on Photo-morphogenesis.

Besides the multifarious influence of light over plants, it has far reaching effects on the various biological activities of animals such as growth, development, reproduction, locomotion, pigmen­tation, metabolism, Photoperiodism, Effect on Eyes, etc.

2.  Temperature

Temperature is a measurement of the degree of heat. Like light, heat is a form of energy. The radiant energy received from the sum is converted into heat energy. Heat is measured in calo­ries. The temperature at which physiological processes are at their maximum efficiency is called optimum temperature.

The mini­mum, optimum and maximum temperatures are called cardinal temperatures. The cardinal temperature varies from species to species, and in the same individual from part to part. The distributions of plants, animals are also influenced by tem­perature.

Temperature plays an important role in affecting the structure physiology, growth and distribution of plants and animals, such as Effect on cell and Protoplasm, Effect on Metabolism, Effect on Respiration, Effect on Development, Effect on Transpiration in Plants, Effect on Reproduction, Effect on Sex-ratio, Effect on Morphology, and Effect of Colouration.

3. Water

Water is an indispensable part of land and soil productivity. The misuse of water leads to soil degradation and erosion. Proper management of water is highly necessary for better production. Water is also indispensable for human beings.

Thus, it goes without saying that water is the most important substance necessary for life. All the physiological processes take place in the medium of water. Protoplasm, the very basis of life, is made up mostly of water. Plants and animals show considerable variation in their re­quirements of water.

On the basis of nature of soil, the water requirement of different plants and animals are as follows:

·         Hydrophytes : Plants living in water require large quanti­ties of water.

·         Xerophytes: Terrestrial plants which cannot tolerate ex­tremely dry conditions and pass through long periods without-water.

·         Mesophytes : Terrestrial plants require moderate quan­tity of water.

Similarly, animals also belong to three important ecological groups depending on the requirement of water:

·         Hydrocoles: Aquatic animals which live in water and require large quantity of water

·         Xerocoles : Terrestrial animals which can tolerate ex­tremely dry conditions and pass long periods without water.

·          Mesocoles : Terrestrial animals requiring moderate quan­tity of water.

4.  Rainfall

The main source of soil water is precipitation. The rainfall pro­vides water to plants and animals. Rainfall occurs due to inter­change of water between earth’s surface and the atmosphere. This is known as the hydrologic cycle. In this cycle two important things are precipitation and evapo-transpiration.

Annual rainfall determines the types of vegetation in any re­gion. We find evergreen forests in tropical regions due to heavy rainfall throughout the year. Grasslands are found in such regions where there is heavy rainfall during summer and low rainfall dur­ing winter.

Different regions of the earth receive, different quantity of rain­fall depending upon the geographical features and the availability of moisture laden winds. The quantity, duration and intensity of rainfall regulate plant life. Only a part of the rain water is used by the plants, the rest is lost in many ways like evaporation and run-off. Thus, there is a difference between the actual rainfall and the effective rainfall. The evaporation is governed by the moisture content and the temperature of the atmosphere, and hence, in effective rainfall the total rainfall in relation to temperature is taken into account.

The quantity of water that a soil holds or that infiltrates into the soil depends upon the properties of soil and type and den­sity of vegetation covering it. In a bare area, the rain drops beat the compact surface of the soil and loosen the soil particles which are washed away. Though most of the plants cannot make use of atmospheric humidity, several lichens, filmy ferns and epiphytic orchids can absorb humidity from the air.

5.  Humidity

Atmospheric moisture in the form of invisible vapour is known as humidity. Humidity is greatly influenced by intensity of solar radiation, temperature, altitude, wind, water status of soil etc. Low temperature causes higher relative humidity by decreasing the capacity of air for moisture. Processes as transpiration, ab­sorption of water etc. are influenced by atmospheric humidity. Humidity, thus, plays an important part in the life of plants and animals.

6. wind

Air in motion is called wind. It is a vital environmental factor. It affects plants, and other organisms. It modifies the water rela­tion and light conditions of a particular region. Wind brings about a number of physical, anatomical and physiological changes of plants. Such changes are breakage and uprooting of plants, de­formation, erosion and deposition,, salt spray etc.

The wind accelerates transpiration, removes solid moisture and at high velocities causes soil erosion. Erosion is the removal of the surface soil, rich in organic matter and fine mineral parti­cles. Excessive transpiration leads to desiccation and death of apical meristems. Thus, the plants tend to become dwarf, pro­fusely branched and usually have small leaves. The sand parti­cles blown with the wind deposit on leaf surface and reduce photo-synthesis, cause rise in temperature and lead to rapid des­iccation.

On the exposed mountain tops, plants frequently live in dan­ger of being uprooted and blown away by strong winds. In these situations, the vegetation is largely composed of species with a prostrate habit of growth and a tenacious underground root or rhizome system.

7.  Atmospheric Gases

Some principal gases like nitrogen, oxygen, carbon-dioxide, helium, hydrogen, methane, ozone etc. are found in atmosphere. In addition to these gases, there are water vapours. Industrial gases, dust, smoke particles, micro-organisms etc. are present in the atmosphere. These gases have important influence on the environment.

2.  Topographic or Physiographic factors

 The factors concerned with physical geography of the earth are known as topographic factors. These factors influence vegetation which causes variation in climate of a geographic region, ultimately give rise to a characteristic microclimate.The different topographic factors are:

1. Altitude of the place:

As the altitude above the sea level increases, there happens a decrease of temperature. Besides, the values of pressure, humidity, wind velocity etc. also changes. All these factors together give a definite pattern of vegetational zone.

2. Steepness and Exposure of the slope:

The slope of mountain affects the nature of vegetation. In northern hemisphere, south facing slopes receives more solar radiation than the north facing slope. This may be due to the fact that the steep southern slope receives the solar radiation almost at right angles during the mid-day whereas the northern slopes receive only oblique rays during morning and evening hours. This difference in solar radiation brings about a change in vegetation in the two sides of the slope.

In addition to this, the steepness of slope accelerates the downward movement of surface water. The downward movement of water over the slope causes soil erosion and as a result, the vegetation disappears from that area.

3.  Direction of mountain chains:

The direction of mountain chains considerably influences the rainfall in an area. If the moun­tain chains lie in the path of wind full of water vapour, then there is heavy rainfall on the wind striking side on the mountain chain.

3.  Edaphic factors:

Edaphic factors deals with different aspects of soil, such as the structure and composition of soil, its physical and chemical fea­tures. A galaxy of complex factor constitutes the soil. Soil is usually defined as “any part of earth’s crust in which plants root”. The soil is constituted as a result of long-term proc­ess of complex interaction leading to the production of a mineral matrix in close contact with interstitial organic matter both living and dead.

After a long time, the parent mineral matter takes the modified shape which forms soil. The interactions among climatic, topographic and biological factors pave the process of transfor­mation and modification of mineral matter into soil. Thus, soil has mainly the following components: Mineral matter, Soil organic matter or humus, Soil water/soil solution, Soil Atmosphere,  Biological system (fauna of bacteria, fungi, algae, proto­zoa, ratifies, arthropods, etc.). The soil development may be classified into two major phases Weathering of parent rock and Maturation profile development.

a.      Weathering:

The weathering is the process by which large rocks are broken down to small pieces and converted to a fine powder. This is a long-term process occurring mostly under the influence of the climatic conditions of the area, and hence called weathering.

The mechanical or physical weathering takes places by the movement of rocks with running water or ice (as in rivers and glaciers) and by action of gravitational forces as landslide in moun­tainous regions. The freezing of water in small crevices in the rocks may also exert enough pressure to breakdown rocks into pieces.Biological weathering includes the action of various organisms, particularly lower plants (lichens and mosses) which secrete vari­ous organic acids, and produce humic acids after death and de­cay. These acids help in the weathering process.

b.      Maturation:

The maturation process determines the struc­ture of the soil profile and the type of the soil. It is largely influ­enced by the prevalent climatic conditions, and indirectly by the type of vegetation found in that area.

There are four major maturation processes:

(a) Melanization: The humus derived from the dead organic matter gets mixed in the upper layers of the soil which become dark coloured. It occurs mostly in the regions of low humidity.

(b) Podzolization: In regions with high rainfall or high hu­midity and low temperature, the minerals in the humus get leached from the upper horizon and get precipitated in middle of B horizon (alluvial) forming a hard pan. This leaves an ash-coloured surface layer of the soil from which the soil derives its name Podzol.

(c) Gleization: In very cold climates the underground water lying above the rock layer continuously reacts with the partly weathered mineral matter. The hydrolysis and re­duction of the minerals result in the formation of a hard gley horizon.

(d) Patternisation: In very hot and humid climate, the rapid decay of organic matter and release of base from organic combination result in the solubility of silica and forma­tion of oxides of iron, aluminium and manganese, etc. This results in a red coloured soil, usually rich in iron, and deficient in bases and organic matter.

4. Biotic factors:

Under natural situations, organisms live together with their inter­actions directly and indirectly. The biotic factors constitute the living organisms of the environment and definitely they have their interactions. The population occurring together in an area interacts with each other in several ways. In the study of environmental reactions of a particular kind of organisms, these interactions are generally referred to as the biotic factors.

We can elaborate in detail the relationship found in biotic factor, influencing the environment. Ecologists use the term symbiosis which means living together. All types of interactions including parasitism have been included under “symbiosis.” Symbiosis means interaction of living organ­isms which are naturally beneficial..

Odum has analysed the aforesaid interaction into two main groups. These are:

1.  Positive Interactions:

When the populations help one another and either one or both the species are benefited, the interactions are known as positive interactions. The benefits may be in respect of shelter, food, substratum or transport and the association may be con­tinuous or transitory, obligate or facultative and the two partners may be in close contact or one of them may live within a specific area of the other or attached to its surface. The beneficial interac­tions are:

·         Mutualism:

Mutually beneficial inter-specific interactions with permanent and obligatory contact indispensable for their survival is termed as mutualism. Generally, two species (population) enter into some contact beneficial to each other.

Some examples of mutualism are as follows:

(i) Pollination by Animals: Bees, moths, butterflies etc. de­rive their food from plants and bring about pollination.

(ii) Dispersal of fruits and seeds: Generally, the animals dis­perse the fruits and seeds. The birds eat the fruits and the seeds contained in fruits are left through excrement at different places.

(iii) Symbiotic nitrogen fixers: The bacterium Rhizobium forms nodules in the roots of leguminous plants and lives symbiotically with the host. Bacteria derive food from the higher plants and in return fix gaseous nitro­gen which is necessary for the plants.

·         Commensalism:

Commensalism represents two or more populations living to­gether without entering into any kind of physiological exchange. In this process, one is benefited without any effect on the other. A commensal which lives upon the hosts is called as ectocommensals.

A variety of micro-organisms, saprophytic bacteria and fungi, and protozoans live within tissues or cavities of higher plants and animals. There are many commensals which make temporary contact with other organisms. Squirrels, monkeys, tree frogs, birds and snakes belong to this category.

From the living root as well as leaves of higher plants, there is a continuous diffusion of their metabolic products like sugar and amino acid. These are the sources of nutrient for micro-organ- isms. These micro-organisms supply protection to roots and leaves against attack by pathogens. Some metabolic products are pro­duced by micro-organisms. These are specified as auxins. These microbes play a vital role in controlling the growth and develop­ment of the higher plants.

·         Proto-Co-Operation:

The positive relationship between populations, mutually ben­efiting each other has been termed as proto-co-operation. Such association of populations is non-obligatory mutualism. Exam­ple of proto-co-operation is sea anemone. Adamsia palliate is at­tached to the shells or hermit crab. The sea anemone is carried by the crab to fresh feeding sites. The crab is also protected from its enemies by sea anemone.

2. Antagonism or Negative Interactions:

The relationship between members of different species in which one or both are harmed is termed as antagonism. This has been referred to as negative interactions.The relationships of an­tagonism include:

·         Antibiosis:

Through the production of some substances or environmen­tal conditions due to metabolic pathways, there is death of one organism by another. This is termed as antibiosis. Productions of chemicals which are antagonistic to microbes have been referred as antibiotics.

·         Parasitism:

A parasite is the organism living on or in the body of another organism and deriving its food from its tissues. A galaxy of plants and animals are parasites in their mode of existence. Species of cuscuta grow on other plants on which they depend for nourish­ment.

·         Predation:

Predator is free living organism which kills and devours individuals of other species. The parasite which lives on or in its host derives nourishments without killing it, whereas the preda­tor kills and devours its prey. Carnivore’s animals are predatory.

·         Competition:

When two organisms survive for something which is inadequate leads to competition. Darwin (1859) in his famous work, “On the Origin of Species Through natural Selection” has highlighted the concept of struggle between species. Plants compete for light, nutrients in a forest and animals for food and shelter.

Competition may be Intra-specific competition occurs between the members of same population. Inter-specific competition occurs between the populations of different species. It is known as interference com­petition. The intra-specific competition is the basis for the develop­ment of theory of natural selection and evolution of species. In­ter-specific competition between plants may be found itself by chemical aggression or allelopathr. A population cannot tolerate a certain range of temperature, humidity, etc. Thus, any popula­tion can only survive and reproduce within certain environment limits.

5. Limiting Factors:

A limiting factor is that substance of quality in the environment, j the supply of which is least abundant or over abundant in rela­tion to the need of the living organism concerned. Limiting factors are of two types on the basis of their correlation with population density:

1. The Density Dependent Limiting Factor:

The effect of such type of limiting factor has direct correlation with population density. The influence of limiting factor increases j with the increase in population density. For example, food sup­ply is density dependent. Higher the population density lower food will be available to eat and higher will be food scarcity.

2. The Density Independent Limiting Factor:

The effect of such type of limiting factor is limited to many or few individuals without reference to the population level. For example, flood is density independent. It may wipe out entire population of a species whether these are few or many. Besides, the other limiting factors which influence living organisms are the various environmental factors. The environmen­tal factors may be abiotic or biotic. The abiotic factors are either physical factors (light, temperature, water, soil, wind, etc.) and chemical factors (nutrients). The nutrients may be divided into macro-nutrients (required in large quantities) and micro-nutrients (required in traces).

The essential macro-nutrients for plants are carbon, oxygen, nitrogen, phosphorous, sulphur, potassium, cal­cium and magnesium. The essential micro-nutrients are boron, chlorine, sodium, copper, iron, manganese, Zinc vanadium, and molybdenum.

Daftar rujukan

Environmental polution.2016. 5 Ecological Factors that Constitute the Environment of an Organism. (online), (http://www.environmentalpollution.in/environment/5-ecological-factors-that-constitute-the-environment-of-an-organism/178), diakses 25 januari 2017.