Environmental Factors – Abiotic and Biotic Components of Ecosystem

The Biology Topics of ecology involve studying the relationships between living organisms and their environment.

Abiotic and Biotic Factors in the Environment – Meaning, Differences & Examples

Environmental factors directly or indirectly regulate the growth, reproduction, and life cycle of the living organism. The classification of environmental factors is as follows.

Abiotic Factors

Except for living factors, all non-living factors in the ecosystem are abiotic factors. Abiotic factors are divided into three categories Physical, Inorganic, and Organic factors and Physiographic or Topographic factors.

A. Physical Factors

Solar energy, light, air, temperature, humidity, wind atmospheric pressure are the primary physical components that help to maintain the vitality of the living world.

1. Solar energy:
Green plants are able to convert solar energy into chemical energy that is stored as potential energy in food substances. Consumers take this good and thus a relationship between producers and consumers in maintained in the ecosystem.

2. Light:
It is the primary source of energy in the living world. Various life processes are influenced directly or indirectly by this factor. It also affects the distribution, colour, and certain structures in terrestrial animals. It influences their pigmentation (skin colour) in several ways. In birds, light effects reproductive activities. The light factor also affects the orientation, behaviour, and normal daily activities of terrestrial animals. For example, cockroaches, moths, bats, etc., are active during light.

Light is also one of the major factors controlling the distribution, movement, colouration, and development of certain structures in aquatic organisms. The occurrence of bioluminescence in the sea is the result of low intensities of light.

During photosynthesis plants produce their food, when sunlight is available as the major source of energy. The presence of light on the land surface is closely related to that of the temperature, where the sun is the source for both. Other life processes of organisms like growth, transpiration, germination, movements, and photoperiodism, also are all related to light. In the case of growth, it is favoured by moderate light intensity. The rosette habit of plants is also favoured by the UV-radiations. During light, stomata open whereas they close in darkness. So transpiration is promoted by the light.

Photoblastic seeds are sensitive to light, these seeds germinate only in the presence of light, e.g., Rumex, and Lactuca. As well as germination is also effected by the light. Pigmentation, movement of such small photosynthetic organisms, and photoperiodism are all initiated and properly respond to the duration of light. Fondness of light, plants are of two types

• Heliophytes: Plants growing in bright light.
• Sciophytes: Sciophytes grow well under shade. They are adapted to low intensity of light.

In the light, photosynthesis in plants occurs. In high light intensity, C4 and CAM plants are assimilate more carbon, than C3 plants. In case of animal, Euglena, a single celled animal is positively phototactic but copepod like zooplantktons are negetively phototactic.

Differences between Heliophyte and Sciophyte Plant:

Heliophyte	Sciophyte
1. Plants thrive in higher intensity of light.	1. Sciophytes need less intensity of light.
2. Leaves are dark green and internodes are short.	2. Leaves are light green and internodes are long.
3. Lenticels are in the lower epidermis of the leaf.	3. Lenticels are on both sides of the leaf.

Light Zones in Aquatic Habitat: The aquatic habitat is also affected by the different zones of light. There are two main zones are Littoral zone and the Limnetic zone.

• Littoral Zone: Littoral zone is a shallow coastal region where light is able to pass through the shallow water and reach the bottom.
• Limnetic Zone: Limnetic zone is an open water zone where water is deep and the amount of oxygen and light decreases with the depth.

This limnetic zone is further divided into 3 parts:

• Photic Zone: The limnetic zone, is the upper part where light can easily penetrate. The upper and lower part of the photic zone, are called a euphotic and disphotic zone. In the euphotic zone where light received is more than the compensation point, similarly in the disphotic zone, where received light is below the compensation point.
• Profundal zone: Profundal zone is a zone of deep water where light does not easily penetrate.
• Benthic zone: Benthic zone is the bottom zone where light does not penetrate.

3. Temperature:
It may be divided into three types – optimum, maximum, and minimum. An optimum temperature is necessary for the processes of growth and development to proceed at a normal rate. In this temperature range, all life processes function smoothly and efficiently. The chemical constituents of the protoplasm suffer a considerable range at around 38°C. The proteins, one of the chief constituents of the protoplasm, become denatured and coagulated at considerably high temperatures. However, the average maximum temperature for living organisms lies between 40°C-45°C.

According to temperature, plants are divided into four types-

• Megatherms: The area where plants are growing in high temperatures, e.g., Tropical rainforest.
• Mesotherms: The area where plants can tolerate moderate temperature, e.g., Tropical deciduous forest.
• Microtherms: A plant requiring a mean annual temperature between 0° and 14°C for full growth.
• Hekistotherm: A cold-tolerant plant of polar regions.

4. Humidity:
Humidity together with light and temperature plays a vital role in regulating the activities and distribution of organisms. The atmospheric humidity influences the form and structure of plants. It directly affects the transpiration rate in plants. Animals in rainforests live only when the air is almost saturated with moisture. On the other hand, desert animals live where the air is extremely dry.

5. Wind:
Wind exerts an influence on both the configuration and distribution of plants. It also affects other factors like water content and temperature in a given area, through its effect on evaporation. The direct effect of strong winds in mechanical leading to the uprooting of trees and permanent curvatures in plants. Indirectly, it affects the transpiration rate by making the air surrounding the plants the most. Wind is also involved in the dispersion of pollen, seeds, and fruits.

6. Atmospheric Pressure:
It exerts its own impression on the living world. It varies inversely with altitude. Low atmospheric pressure results in low oxygen pressure – a harmful condition due to less oxygenation of tissues.

7. Precipitation:
Precipitation is water released from clouds in the form of rain, freezing rain, sleet, snow, or hail. It is the primary connection in the water cycle that provides for the delivery of atmospheric water to the earth. Most precipitation falls as rain.

B. Inorganic Factors

The inorganic factors are water, soil, and mineral elements, which are involved in the material cycle.

1. Water:
It is one of the most important physical factors that affects the vital processes of all living beings. Water with mineral nutrients in the soil is absorbed by plants. It provides the habit for a number of organisms. Along with other factors, it regulates the structure and distribution of plants and animals. Water actions also influence the distribution of organisms. Thus the differences between a lotic and a lentic community are mainly due to a substantial difference in the current factors.

2. Soil:
Soil is the upper part of the earth’s surface which is humus humus-containing part. The nature of soil in different places is different i.e., dependent on the climate. The different characteristics of soil are soil composition, soil texture, soil porosity, soil air, soil pH, soil water, etc.

Soil Composition:
Soil is composed of mineral particles, organic matter, air, and water. Soil mineral particles include sand, silt, and clay. Soils are also composed of organic matter, which includes living biomass, detritus (dead tissue), and humus (non-living). Humus is an amorphous and colloidal mixture of complex organic substances.

Soil Porosity:
There are several pore spaces, occu¬pied in the percentage of soil volume. These pores are 2-types Macropores and Micropores.

Soil Air:
Soil air is essential for roots and all soil organisms. Around 25% of the total volume of the soil is filled with air in case of good soil. Oxygen and carbon dioxide are important constituents that affect processes like nitrification and denitrification. Generally, soil air is richer in carbon dioxide.

Soil pH:
pH determines the acidity and alkalinity level. The soil pH determines the type of soil microorganism, solubility of different mineral components, and growing plant types. Saline soils contain an excess of salts.

Soil Water:
It is one of the most important characteristics of soil. Soil water is mostly derived from rain and running water. On the basis of the position of water in the soil, there 4 different types as Hygroscopic water, Capillary water, gravitational water, and chemically bound water.

Soil texture:
The relative proportions of sand (0.05 – 2.0 mm), silt (0.002 – 0.05 mm) and clay (< 0.002 mm) in soil is referred to as soil texture. According to the proportion of these three components soils are classified into sands, silt, clays, and loams.

• Sands: The sand group includes all soils in which the sand separates make up at least 70% and the clay separates 15% or less of the material by weight. The properties of such soils are therefore characteristically those of sand in contrast to the stickier nature of clays.
• Silt: The silt group includes soils with at least 80% silt and 12% or less clay. Naturally, the properties of this group are dominated by those of silt.
• Clays: To be designated clay soil must contain at least 35% of the clay separate and in most cases not less than 40%. In such soils, the characteristics of the clay separates are distinctly dominant.
• Loams: An ideal loam may be defined as a mix¬ture of sand, silt, and day particles that exhibits the properties of those separates in about equal proportions.

Soil Profile:
The mineral and organic components of soil are differentiated into horizons or start of variable depth. Each horizon differs in morphology, physical structure, and chemical and biological characteristics. These horizons are evident when a vertical cut is made through the soil, revealing the soil profile. The structure of the soil profile is as follows.

• The O-horizon: This is the uppermost layer of the organic litter of loose leaves and debris. This horizon of soil is often black-brown or dark brown in colour due to the presence of organic content.
• The A-horizon or Topsoil: This layer is rich in organic material and is known as the humus layer. This layer is dark in colour and seed germination takes place here.
• The E-horizon: This layer is composed of nutrients leached from the O and A horizons. This layer is more common in forested areas.
• The B-horizon or Subsoil: It is the subsurface horizon, present just below the topsoil and above the bedrock. It contains less humus, soluble minerals, and organic matter and is lighter brown due to the presence of clay soil.
• The C-horizon or Saprolite: This layer of parent rock is devoid of any organic matter and is weakly weathered.
• The R-horizon: This is unweathered bedrock made up of compact rocks such as granite, basalt, and limestone.

Physiologically dry soil: In some areas where halophytic plants grow, the soil contains a huge amount of salts like sodium chloride, magnesium chloride, magnesium sulphate, etc. The presence of such salts in the soil interferes with the absorption of water by these halophytic plants. This saline soil is termed physiologically dry soil.

3. Minerals:
Minerals are naturally occurring substances i.e., solid and usually biogenic. It is different from a rock which can be an aggregate of minerals or non-minerals and does not have a specific chemical composition. Potassium, calcium, sulphur, magnesium, phosphorus, iron, etc., are all vital mineral components as part of inorganic components.

C. Organic Factors

The organic factors of the ecosystem are proteins, carbohydrates, lipids, amino acids, dead and decomposed body, humus, urea, etc., all of which are synthesized in the biotic phase. These organic factors produce a connecting link between living and non-living as biochemical substances.

D. Physiographic or Topographic Factors

The altitude, undulating landscapes, amount of light falling on a place or wind blowing through the region, steep slopes, etc., constitute the topographic factors of an ecosystem.

1. Height or Altitude:
Higher altitude (mountains, hills, etc.) is characterized by low temperature, high velocity of wind, lower atmospheric pressure, high humidity, and rainfall. The temperature decreases with the increase in height and the lower temperature favour the formation of clouds and rain. Thus, the mountains and hills are favourable for plant growth and cause different types of forests due to the above climatic variations. However, at very high hills and mountains the water vapours directly condense into snow and cause poor vegetation.

2. Direction of the Slope:
It is generally observed that the sunward direction of the slope is warmer compared to the opposite, because, the duration of sunlight is the longest in the sunward direction. It also gets good rainfall. Thus, the sunward-directed slope possesses good vegetation whereas the vegetation is poor in the opposite direction due to little or no direct solar radiations.

3. Steepness of the Slope:
The steepness of the slope allows the rapid flow of rainwater and causes a water deficit. The rapid movement of water over the slopes causes erosion of the topsoil and thus the vegetation disappears from the area. On the other hand, a plain soil surface slows the water movement and allows it to soak in the soil. It also receives sunlight for a long duration. Thus, the less steep area is best suitable for plant growth.

Responses to the Abiotic Factors

Abiotic factors like light, temperature, water, rain, various gaseous components, humidity, etc., influence the life pattern of the organism in a particular region. In different times those factors create unfavourable conditions for organisms but that organism actively adapts to the unfavorable environmental condition and survives successfully. According to the external environment, the whole living organism can be classified into the following four-

1. Regulators
This type of organism physiologically and biochemically adjusts to unfavourable conditions and survives. Due to the process of homeostasis, the animal can maintain their internal body temperature and pH balance. The birds and mammals whose internal temperature is always constant, are called homeothermal animals. Regulators are able to withstand differences in their external environment because they can control their internal environment. This allows regulators to increase the possible ecological niches that they can inhabit. However, this regulation requires energy, so regulators tend to have high metabolic rates.

All birds and mammals, a very few lower vertebrates and invertebrates are regulators (thermoregulation and osmoregulation). For example, human beings maintain their body temperature by sweating in the summer and shivering during the winter season. Plants do not have such mechanisms to maintain internal temperatures.

Osmoregulation is the active regulation of the osmotic pressure of an organism’s body fluids to maintain the homeostasis of water content; that is it maintains the fluid balance and the concentration of electrolytes (salts in solution) to keep the fluids from becoming too diluted or too concentrated. Osmotic pressure is a measure of the tendency of water to move into one solution from another by osmosis. The higher the osmotic pressure of a solution, the more water tends to move into it. Pressure must be exerted on the hypertonic side of a selectively permeable membrane to prevent diffusion of water by osmosis from the side containing pure water.

Organisms in aquatic and terrestrial environments must maintain the right concentration of solutes and amount of water in their body fluids; this involves excretion (getting rid of metabolic nitrogenous wastes and other substances such as hormones that would be toxic if allowed to accumulate in the blood) through organs such as the skin and the kidneys. Osmoregulators tightly regulate their body osmolarity, maintaining constant internal conditions. They are more common in the animal kingdom. Osmoregulators actively control salt concentrations despite the salt concentrations in the environment When the osmotic concentration of body fluid is more than the osmotic concentration of the surrounding environment is known as hyperosmoregulator.

An example is freshwater fish. The gills actively uptake salt from the environment by the use of mitochondrial cells. Water will diffuse into the fish, so it excretes a very hypotonic (dilute) urine to expel all the excess water when the osmotic concentration of body fluid is lower than the osmotic concentration of the surrounding environment is known as hypoosmoregulator. A marine fish has an internal osmotic concentration lower than that of the surrounding seawater, so it tends to lose water and gain salt. It actively excretes salt out from the gills. Most fish are stenohaline, which means they are restricted to either salt or fresh water and cannot survive in water with a different salt concentration that they are adapted to. However, some fish show a tremendous ability to effectively osmoregulate across a broad range of salinities; fish with this ability are known as euryhaline species, e.g., Flounder. Flounders have been observed to inhabit two utterly disparate that is essentially separate kind of environments marine and fresh water and it is inherent to adapt to both by bringing in behavioral and physiological modifications.

Some marine fish, like sharks, have adapted a different, efficient mechanism to conserve water, i.e., osmoregulation. They retain urea in their blood in relatively higher concentrations. Urea damages living tissues so, to deal with this problem, some fish retain trimethylamine oxide (TMAO). This provides a better solution to urea’s toxicity. Sharks, having slightly higher solute concentration (.i.e., above 1000 mosm (milliosmole) which is sea solute concentration), do not drink water like freshwater fish.

Osmoregulation in Plants:
While there are no specific osmoregulatory organs in higher plants, the stomata are important in regulating water loss through evapotranspiration, and on the cellular level the vacuole is crucial in regulating the concentration of solutes in the cytoplasm. Strong winds, low humidity and high temperatures all increase evapotranspiration from leaves. Abscisic acid is an important hormone in helping plants conserve water – it causes stomata to close and stimulates root growth so that more water can be absorbed.

Plants share with animals the problems of obtaining water but, unlike in animals, the loss of water in plants is crucial to create a driving force to move nutrients from the soil to tissues. Certain plants have evolved methods of water conservation. Xerophytes are plants that can survive in dry habitats, such as deserts, and are able to withstand prolonged periods of water shortage. Succulent plants such as cacti store water in the vacuoles of large parenchyma tissue. Other plants have leaf modifications to reduce water loss, such as needle-shaped leaves, sunken stomata, and thick, waxy cuticles as in the pine. The dense roots of marram grass help stabilize sand dunes. They have rolled leaves with stomata on the inner surface.

Hydrophytes are plants in water habitats. They mostly grow in water or in wet or damp places. In these plants the water absorption occurs through the whole surface of the plant, e.g., the water lily. Halophytes are plants living in marshy areas (close to the sea). They have to absorb water from such soil which has higher salt concentration and therefore lower water potential (higher osmotic pressure). Halophytes deal with this situation by activating salts in their roots. As a consequence, the cells of the roots develop lower water potential which brings in water by osmosis. The excess salt can be stored in cells or excreted out from salt glands on leaves. The salt thus secreted by some species helps them to trap water vapours from the air, which is absorbed in liquid by leaf cells. Therefore, this is another way of obtaining additional water from the air, e.g., glasswort and cord grass.

Mesophytes are plants living in lands of temperate zone, which grow in well-watered soil. They can easily compensate for the water lost by transpiration by absorbing water from the soil. To prevent excessive transpiration they have developed a waterproof external covering called cuticle.

Osmoregulation in Animals:
Kidneys play a very’ crucial role in human osmoregulation by regulating the amount of water reabsorbed from glomerular filtrate in kidney tubules, which is controlled by hormones such as antidiuretic hormone (ADH), aldosterone, and angiotensin II. For example, a decrease in water potential of detect¬ed by osmoreceptors in the hypothalamus, which stimulates ADH release from the pituitary gland to increase the perme¬ability of the wall of the collecting ducts in the kidneys. Therefore, a large proportion of water is reabsorbed from fluid to prevent a fair proportion of water from being excreted.

A major way animals have evolved to osmoregulate is by controlling the amount of water lost through the excretory system.

• Stenohaline organisms can tolerate only a relatively narrow range of salinity.
• Euryhaline organisms are tolerant of a relatively wide range of salinity.

2. Conformers
Conformers tend to have low metabolic costs and a narrow ecological niche unless they can withstand change in the external environment. For example, the temperature of a heat conformer, like a snake or lizard, will change as a result of the environment it is in. Conformers must change their behaviour in order to survive under extreme circumstances. Behavioural responses by conformers include reducing their activity when the environmental temperature falls.

A common way in which conformers maintain an optimum temperature is to bask in the sun and absorb the heat energy directly or from the ground around them. Some desert lizards burrow under the surface of the sand in order to cool down or warm up depending on what time of day it is. Spider crabs are able to conform to the salinity in their environment as they can lose or gain water to match their external environment.

Osmo conformers are marine organisms that maintain an internal environment that is isoosmotic to their external environment. This means that the osmotic pres¬sure, or osmolarity, of the organism’s cells, is equal to the osmotic pressure of their surrounding environment. Minimizing the osmotic gradient subsequently minimizes the net influx and efflux of water into and out of cells. Even though osmoconformers have an internal environment that’s isoosmotic to their external environment the types of ions in the two environments differ greatly in order to allow critical biological functions to occur. A benefit to osmoconformation is that organisms don’t need to expend as much energy.

Most osmoconformers are marine invertebrates such as echinoderms (such as starfish), mussels, marine crabs, lobsters, jellyfish, ascidians (sea squirts-primitive chordates), and scallops. Some insects are also osmoconformers. Some osmoconformers, such as echinoderms, are stenohaline, which means they can only survive in a limited range of external osmolarities. The survival of such organisms is thus contingent on their external osmotic environment remaining relatively constant. On the other hand, some osmoconformers are classified as euryhaline, which means they can survive in a broad range of external osmolarities. Mussels are a prime example of an euryhaline osmoconformer. Mussels have adapted to survive in a broad range of external salinities due to their ability to close their shells which allows them to seclude themselves from unfavorable external environments.

Difference between Regulators and Conformers

Regulators	Conformers
1. Here they maintain constant homeostasis.	1. Here homeostasis is little.
2. Regulator maintains their body temperature.	2. According to the environment, their body temperature changes.
3. Regulator consumes a large amount of energy.	3. Conformers consume a lesser amount of energy.
4. They are more active.	4. They are less active.

3. Migration
Migration means the movement of organisms from extremely unfavourable conditions to favourable conditions. For example, many aquatic animals like Eel, Salmon, Whale move from one place to another for favourable environment.

4. Suspension of growth
Due to extremely unfavourable environmental conditions, the proper growth of the organism stops. As an example, bacteria produce endospores to resist unfavourable conditions. Entamoeba like parasites resists the unfavourable situation through the formation of cyst.

Biotic Factors

Plants, animals, and microbes constitute the biotic factors. On the basis of a functional point of view, the living organisms of the ecosystem are divided into two factors by Odum (1966), e.g., Autotrophs or producers and heterotrophs or consumers.

1. Autotrophs
Autotrophs, in which the organisms fix light energy, utilize substances like carbon dioxide and water to produce complex food materials. All green plants containing chlorophyll, are known as autotrophs. They produce their own food by photosynthesis, therefore they are called producers. Such synthesized food is used by consumers and decomposers.

Producer
Producers are the autotrophic organisms, i.e., green plants which are able to manufacture food from simple inorganic substances in the presence of light energy and chlorophyll by photosynthesis yielding carbohydrates, proteins, fats, and other complex materials. In general, all green plants are known as producers. However, in a true sense, green plants only convert solar energy into chemical energy of food. So, in terms of energy, green plants are actually converters of energy or transducers.

There are certain bacteria that can prepare their own food through the chemosynthesis process. So, those bacteria are also producer organisms. A part of synthesized food is used by the producers themselves and the remaining portion is used by the consumers and decomposers. In this process, a part of the solar energy is stored within the producer’s body as potential energy and again consumers release this energy by respiration process as heat and kinetic energy.

2. Heterotrophs
Heterotrophs, in which the organisms utilize, rearrange and decompose the complex materials, that are synthesized by the autotrophic organism. Except for some plants, all animals depend directly or indirectly on autotrophs for their food, therefore, they are called consumers.

Consumer
Consumers are heterotrophic organisms that ingest other organisms or particulate organic matter. Animals mainly depend directly or indirectly on the producer for their food, therefore, they are entitled as consumers. Consumers are of two types Macroconsumers or phagotrophs, Microconsumers or decomposers.

(i) Macroconsumers:
These include relatively big heterotrophic organisms, largely animals that ingest other organisms or food synthesized by the producers. Macroconsumers are of three kinds Primary consumers, Secondary consumers, Tertiary consumers, and Quaternary consumers.

• Primary Consumers (Consumers of first order): The plant-eaters are called primary consumers. They include minute zooplankton like Cyclops, Daphnia, Stenocypris, Protozoa etc. Some phytoplankton like Brachionus, Asplanchna, etc., and some benthic or bottom-form animals like insect larvae, fish, and mollusks act as primary consumers. Primary consumers of land are herbivorous animals, e.g., grasshoppers, pigeons, rabbits, monkeys, goats, cows, etc.
• Secondary Consumers (Consumers of second order): The carnivorous animals feeding on the primary consumers are called secondary consumers, e.g., toads, lizards, and spiders are insect eaters, and dogs, cats, and foxes are small carnivore eaters.
• Tertiary Consumers (Consumers of third order): These are flesh-eaters and eat the dead flesh leftover of the secondary consumers or carnivores, e.g., tigers, lions, whales, sharks, hawks, eagles, vultures, etc.
• Quaternary Consumers: The carnivores that are not killed or rarely killed and eaten by other animals, are called quaternary consumers. Lions, tigers, vultures, etc., are regarded as quaternary consumers.

(ii) Microconsumers or Decomposers:
These are heterotrophic usually microscopic organisms like bacteria and fungi which break down and decompose the complex substances of dead organisms (producers and macroconsumers), absorb the decomposed products, and release inorganic nutrients for reuse by the producers. Thus the decomposer organisms play a very important role within an ecosystem by helping to recycle the materials in the biosphere so that the process of life may go on like an unending chain. The producers, phagotrophs, and saprotrophs, thus, make up the biomass of the ecosystem the living weight.