Abiotic Factors

The non-living elements of an environment are known as abiotic components. These include various physical and chemical factors such as light, temperature, rainfall, atmospheric pressure, pH, and the levels of oxygen and other gases. These factors can change throughout the day and night, as well as across different seasons and years.

1.0Types of Abiotic Environmental Factors

• Certain environmental or ecological factors control the distribution, abundance, growth and reproduction of the organisms comprising the individual members of populations. 
• An environmental factor is any external force, substance or condition which surrounds and affects the life of an organism in any way. 
• Abiotic environmental factors are customarily classified as follows :

Climatic Factors

• Light
• Temperature
• Water (including atmospheric water, rainfall or precipitation, soil moisture, etc.)
• Atmosphere (gases and wind)
• Fire

Topographic or physiographic factors:

• Altitude
• Direction of mountain chains and valleys
• Steepness and exposure of slopes

Edaphic factors: 

• Soil formation, 
• Physical and chemical properties of soil, 
• Nutrients 

2.0Major Abiotic Factors

Light

• It is a complex physical environmental factor. A lux meter or photometer measures light. It is an electromagnetic spectrum.
• The radiant energy from the sun is the basic requirement for the existence of life on Earth. This energy source is of fundamental importance to plants' photosynthetic food production. As mentioned, the world's heat budget depends on solar radiation.
• Visible light: In solar radiation, the wavelength of light or visible spectrum is 400–700 nm. It is also called photosynthetically active radiation (PAR). It is made up of a series of colours ranging from violet to indigo, blue, green, yellow, orange and red, all constituting the visible spectrum.
• Depending upon the penetration of light, oceans are divided into euphotic zones (up to 50 meters in depth), disphotic zones (up to 80 to 200 meters in depth) and aphotic zones (below 200 meters in depth).

Effect of Light on the Plants

Direct effects of light on plants:-

• Formation of chlorophyll pigment.
• A powerful influence on the number and position of chloroplasts.
• Light has its most significant role in photosynthesis.
• Light inhibits the production of auxins or growth hormones.
• The development of flowers, fruits and seeds is greatly affected by light-intensity
• Photoperiodism
• The effect of sunlight on the plant movement is called heliotropism or phototropism

Indirect effects of light on plants:-

• Transpiration
• Absorption of water
• Respiration of plants

Effects of Light on Animals:-

• Effect of light on metabolism
• Effect of light on pigmentation
• Effect of light on animal movements
• Phototaxis: Oriented locomotory movements towards and away from a source of light is called phototaxis
• Phototropisms: The light directed growth mechanisms are called phototropisms
• Photokinesis: Animals when responding to light reduce their velocity of movement and these movements which are non-directional are called photokinesis

Temperature

• Temperature is a vital and dynamic environmental factor that affects every part of the biosphere.
• It plays a crucial role in regulating various life processes, such as behavior, metabolism, reproduction, development (including embryogenesis and blastogenesis), and even death.
• As a universally present factor, temperature often acts as a limiting element in determining the growth and distribution of both plants and animals.
• Most life processes function efficiently only within a certain temperature range, known as the optimum temperature or optimum temperature range.
• Thermal stratification:- The process of differentiation of freshwater habitat into these three strata is called thermal stratification.
• Epilimnion: The superficial layer of fresh water is constantly stirred by wind and is called epilimnion. It is a layer of warmer water, and its temperature may rise to 22°C during summers.
• Hypolimnion: The stagnant water of the bottom constitutes the hypolimnion. The hypolimnion has a temperature of 5°C to 9°C.
• Thermocline or Metalimnion: In between epilimnion and hypolimnion occurs an intermediate zone called thermocline or metalimnion, which has rapid vertical temperature changes.

Effect of Temperature on Plants and Animals:-

1. Metabolism: Different types of enzymes control various metabolic activities of microbes, plants, and animals, and in turn, enzymes are influenced by temperature; consequently, a rise in temperature up to a particular limit increases enzyme activity, resulting in an increased metabolism rate.

2. Reproduction: 

• Different species vary in the maturation of gonads, gametogenesis, and liberation of gametes, which occur at a particular temperature. 
• For example, some species breed uniformly throughout the year, some only in summer or winter, while some species have two breeding periods, one in spring and the other in fall. 
• Thus, temperature determines the breeding seasons of most organisms.

3. Growth: The growth rate of different animals and plants is also influenced by temperature.

4. Morphology:

• Temperature also affects the absolute size of an animal and the relative characteristics of different parts of its body.
• As per Bergman's Rule, birds and mammals can develop larger body sizes in cold regions than in warm areas. Larger species also occur in colder regions.
• Similarly, the extremities of an organism, such as the tail, ears and legs of mammals, appear to be shorter in colder climates, according to Allen's Rule.
• Temperature also influences the morphology of some fishes and is found to have some relation with the number of vertebrae, according to Jordan's Rule.

5. Animal distribution: Because the optimum temperature for the completion of the several stages of the life cycle of many organisms varies, temperature restricts species distribution.

Water

• Water is the most significant factor affecting the life of organisms next to temperature.
• You may think that the organisms living in oceans, lakes, and rivers should not face any problems regarding water, but this is not true. 
• In aquatic organisms, water quality (chemical composition, pH) is also important. 
• Salinity ranges from less than 5 PPT in inland waters through 30-35 PPT in the sea to over 100 PPT in some hypersaline lagoons.
• Some organisms may tolerate a wide range of salinities, such as euryhaline, but others are confined to a narrow range of salt levels. 
• Most freshwater animals cannot live very long in seawater, and vice versa, partly because of the osmotic problems they would face.

Soil

• Soil is the topmost layer of the Earth’s crust, formed through the weathering of rocks.
• It consists of a mixture of both living and non-living components.
• The characteristics and properties of soil vary from one region to another, influenced by factors such as climate, the nature of the weathering process, whether the soil is transported or formed in place (sedentary), and the stage of soil development.
• Key features like soil composition, grain size, and particle aggregation affect important properties such as water percolation and retention.
• These, along with factors like pH, mineral content, and topography, play a crucial role in determining the type of vegetation that can grow in a particular area — which in turn influences the kinds of animals that can be supported.
• Minerals 45% + Water 25% + Air 25% + Organic matter (living + non-living) 5%
• Soil formation is a slow process 1-inch soil is formed in 500-1000 years. 
• Pedogenesis: development of soil or soil formation. Pedology (Edaphology) – the study of soil
• Soil mineral matter: Due to weathering, mineral particles of different sizes are formed.

Soil Organic Matter

• The dead organic matter present in soil is called humus, which is formed by decomposition of plant and animal remains. 
• Freshly fallen plant and animal material called detritus or litter, partially decomposed litter is called duff. Fully decomposed litter is called humus.

Decomposition (Formation of Humus):-

• It plays a vital role in breaking down complex organic materials into simpler substances such as humus and inorganic compounds like carbon dioxide, water, and nutrients — a process known as decomposition.
• The raw material for this process, called detritus, consists of dead plant parts (like leaves, bark, and flowers), animal remains, and faecal matter. Decomposition occurs through several key steps: fragmentation, leaching, catabolism, humification, and mineralization.
• Detritivores (for example, earthworms) fragment detritus into smaller pieces; this process is called fragmentation. 
• The water-soluble inorganic nutrients leach into the soil horizon and precipitate as unavailable salts. 
• Bacterial and fungal enzymes degrade detritus into simple organic and inorganic substances; the process is known as catabolism.
• All the above-given steps of decomposition act simultaneously on the detritus. Decomposition in the soil leads to humification and mineralization. 
• Humification results in the accumulation of a dark-coloured amorphous substance called humus, which is highly resistant to the action of microorganisms and decomposes at a very slow rate. Colloidal in nature, it thus serves as a reservoir of nutrients. 
• Some microbes further degrade humus, and the release of inorganic nutrients is done by the process known as mineralization.

Soil Profile

Wind Facts

• The strong moving current of air is called wind.
• It is an important ecological factor of the atmosphere that affects plant life differently on flat plains, along sea coasts, and at high altitudes in the mountains. 
• The wind directly involves transpiration, causing mechanical damage and disseminating pollen, seeds, and fruits.
• Wind also modifies the water relations and light conditions of a particular area. Some of the various physical, anatomical, and physiological effects of winds on plants are listed below.

3.0Other Physiographic Factors

• Physiographic factors arise from the structure, form, and dynamics of the Earth's surface. 
• These include topographic or orographic features such as elevation and slope, geodynamic processes like erosion and silting, as well as the characteristics of the local geology

Different physiographic factors can be grouped under the following headings:

Latitudes and Altitudes: 

• Latitude is the distance from the equator. Temperature values are maximum at the equator, which decreases gradually towards the poles. 
• Marked variations in temperature at different latitudes result in the division of earth's vegetation into different zones such as equatorial, tropical rain forests, desert or grasslands, deciduous forests, coniferous forests, alpine forests, tundra and ice and snow of poles. 
• Altitude refers to the height above sea level. At higher altitudes, wind velocity tends to increase, while temperature and air pressure decrease. In contrast, both humidity and light intensity generally rise with elevation.
• Because of these reasons, vegetation at different altitudes is different, showing distinct zonation.

Direction of Mountains and Valleys: 

• The directions of mountain chains or ranges and high mountains act as wind barriers and affect the climate.

4.0Response to Abiotic Factors

• A few organisms can tolerate and thrive in various temperatures (eurythermal). Still, most are restricted to a narrow range of temperatures (such organisms are called stenothermal). 
• The thermal tolerance levels of different species determine their geographical distribution to a large extent.

Regulators:

• Some organisms can maintain homeostasis by physiological means (sometimes behavioural too) wherein constant body temperature, constant osmotic concentration, etc, are maintained.
• Evolutionary biologists believe that mammals' success' is partly because of their ability to maintain a constant body temperature whether they are living in Antarctica or the Sahara desert.
• The mechanisms most mammals have for regulating their body temperature are similar to those in our bodies.
• During summer, as the outside temperature is more than our body temperature, we experience excessive sweating. The resultant evaporative cooling cools the body, much like when a desert cooler is at work. When the outside temperature is much below 37°C, we start shivering - a sort of exercise which generates heat and raises the body temperature.
• However, plants do not have such mechanisms to maintain their internal temperatures.

Conformers:

• Organisms that cannot maintain a constant internal environment have a constant body temperature or osmotic concentration that changes with the external environment.
• Most animals, 99 per cent and nearly all plants cannot maintain a constant internal environment. Their body temperature changes with the ambient atmospheric temperature.
• In aquatic animals, the osmotic concentration of the body fluids changes with that of the ambient surrounding water osmotic concentration. These animals and plants are simply conformers.
• Considering the advantages of a constant internal environment to the organism, we must again.
• Thermoregulation is energetically expensive for many organisms. In small animals, such as shrews and hummingbirds, this is particularly important.

5.0Difference Between Biotic and Abiotic Factors