Ecology; Definition, Meaning, Ecological Hierarchy And Ecological Factors

Introduction To Ecology

Ecology is the scientific examination of interactions between organisms and ecological factors. Ecological factors comprises a multitude of ecological factors, such as light, temperature, soil, air, water, and more, that surround an organism and can potentially impact its growth, distribution, behavior, reproduction, and survival.

It literally means the study organisms in their natural habitats or homes. It is derived from the combination of two Greek words, where “oikos” refers to a dwelling or a place to live, and “logos” means the study of something. Alexander Von Humboldt is often regarded as the father of ecology.

Ernst Hackel, a German zoologist from 1869, stated ecology as the study of the mutually influential relationship between living organisms and their surroundings. E.P. Odum in 1996 described ecology as the exploration of the “structure and function of nature.” The term “ecology” was originally introduced by German biologist (zoologist) H. Reiter in 1868.

The environment consist of several factors, such as light, temperature, soil, air, water, and more, that surround an organism and can potentially impact its growth, distribution, behavior, reproduction, and survival. Synonyms for ecology include hexicology and ethology. Based on living organisms, ecology can be divided into two main branches.

• Autecology, also referred to as individual ecology or species ecology, this ecological study focuses on understanding the relationship between an individual animal or plant species, or its population, and its environment throughout its life history. Autecology examines how specific organisms interact with their surroundings, considering factors such as habitat preferences, resource utilization, reproductive strategies, and other aspects relevant to the survival and well-being of the species.
• Synecology, also known as community ecology, this ecological study explores the relationships between different groups of species, known as communities, and their environment. Synecology examines how different species within a community coexist, compete for resources, interact with each other, and respond to environmental factors. Examples of synecological studies include the investigation of forest communities, grassland communities, aquatic communities, and other types of ecology (ecological communities) found in various habitats.

Ecological hierarchy

The organization of ecological groups is categorized into levels or ranks, known as the ecological level of organization or ecological hierarchy. This hierarchy encompasses various levels, starting from the largest components to the smallest components. The following is a typical sequence of ecological levels:

• Biosphere: The highest level of ecological organization, encompassing all living organisms and their interactions with the physical environment on a global scale.
• Biome: A large-scale geographic region characterized by distinct climate, vegetation, and animal communities.
• Landscape: An intermediate-scale ecological unit consisting of a mosaic of different ecosystems, such as forests, rivers, grasslands, and mountains, within a particular geographic area.
• Ecosystem: A specific area where living organisms (biotic components) interact with the physical environment (abiotic components), including factors like climate, soil, water, and nutrients.
• Community: All the populations of different species living and interacting within a defined ecosystem.
• Population: A group of individuals of the same species living within a specific area and capable of interbreeding.
• Individual: The smallest unit of ecological organization, referring to a single organism of a particular species.

Ecological Factors

Ecological factors are external forces, substances, or conditions that surround and impact the life of an organism in various ways. These factors can be categorized as living or non-living, and they play a significant role in shaping the structure and functioning of ecosystems.  These factors are as follows:

I. Abiotic Components

These are the non-living factors of an ecosystem. It includes climatic, edaphic and topographic factors.

A. Climatic Factors

a. Light

Visible light refers to the radiant energy emitted by the sun, which falls within the wavelength range of 390 nanometers (nm) to 760 nm. This specific range of wavelengths has significant ecological effects and influences various processes in organisms and ecosystems. Some of the important effects of light include:

• Photosynthesis: Photosynthesis relies on the presence of light. The rate at which photosynthesis occurs is influenced by the intensity and duration of light. Optimal plant growth and yield are typically achieved with moderate light levels over an extended period. Red and blue light wavelengths have been found to be particularly effective in driving photosynthesis.
• Chlorophyll formation: Chlorophyll formation is influenced by light, and it significantly affects both the abundance and positioning of chloroplasts.
• Stomatal movement: Stomatal movement, which involves the opening and closing of stomata, is controlled by light. Typically, stomata are open during periods of light and closed during darkness.
• Photoperiodism: The response of plants towards duration of light for flowering is called Photoperiodism. On this basis plants are classified into following types. Short day plant: Plants that require short period (less than 12hrs) of light for flowering is called short day plants. Ex Datura stramonium, Cannabis sativa etc. Long day plants: Plants that require long duration period (more than 12hrs) of light for flowering are called long day plants. Ex Raphanus sativus , Solanum tuberosum. They flower only in summer. Day neutral plant: Plant which show little response to length of light for flowering are called day neutral plants. Ex tomato, cotton, Balsam, etc.
• Movement: Various small photosynthetic organisms like Euglena, Volvox, Chlamydomonas, and others exhibit positive movement, specifically positive phototaxis, towards moderate light. In plants, the aerial parts demonstrate positive phototropism by bending towards the light source. Flowers also exhibit opening and closing responses influenced by light. On the other hand, organisms such as Planaria, earthworms, and slugs display negative movement, known as negative phototaxis, away from light.
• Growth: High light intensity reduces growth but stimulates the development of mechanical tissue in plants. Darkness increases growth, internodal length and size of leaves. Seed germination occurs by the effect of light.
• Reproduction: In animals like birds light initiates the breeding activities. In some birds gonads become active with increased light intensity during summer.
• Overall development of plant parts: Based on their relative requirement and effects of light on their overall vegetative development plants are classified into two types. Heliophytes: Plants which grow in high intensity of light are called heliophytes. They grow best in direct sunlight. Ex. Sal plant. Sciophytes: Plants which grow in defused light are called sciophytes. Ex. Ginger.
• Pigmentation: It influences pigmentation in animals. Prolonged exposure of skin of animals to sun light produces “melanin” which makes the skin dark. Light also induces the formation of chlorophyll pigments in plants.
• Overall effect of light on animals: Light shows various affect on animal life as growth, coloration of body, migration, reproduction etc. Many nocturnal animals prefer to survive without light. It also influences the development of visual organs as eyespots in protozoans, Vesicular eyes in polychaetes, mollusca, compound eye in insects, etc.

b. Temperature

Temperature refers to the measure of hotness or coldness in an environment. It has significant effects on various aspects of organisms, including metabolism, growth and development, coloration, and distribution.

• Metabolism: Metabolism is a fundamental process in living organisms, and it is greatly influenced by enzymes. Enzymes, in turn, are highly sensitive to temperature. An increase in temperature within the range of 17°C to 48°C generally enhances the rate of metabolism. However, once the temperature exceeds 48°C, metabolic activities begin to decline due to the denaturation of enzymes. Extremely high temperatures, typically above 50°C, can be lethal to organisms as the protoplasm coagulates under such conditions. Conversely, temperatures below 0°C can also have detrimental effects, leading to the normal killing of protoplasm. Additionally, it is important to note that the rate of respiration tends to double with each 10°C increase above the optimum temperature.
• Growth and development: There is an optimal temperature range that is conducive to the growth and development of organisms. Extremely low or high temperatures have detrimental effects on these processes. Excessive heat can lead to stunting and eventual death of plants as it negatively affects vital functions such as respiration and transpiration. On the other hand, very low temperatures can cause chilling or freezing injuries in cells due to the formation of ice crystals. Both extreme temperatures hinder proper growth and development. Plants subjected to extreme temperature conditions tend to have limited growth potential due to increased transpiration rates and decreased metabolism.
• Effect on coloration: In certain insects, birds, and mammals, coloration can be influenced by temperature and climatic conditions. In warm and humid climates, these organisms tend to exhibit darker pigmentation compared to those in cooler and drier climates.
• Transpiration and absorption: An increase in temperature generally leads to an increase in the rate of transpiration, which is the process of water loss from plants through their leaves. However, higher temperatures can also impede the rate of absorption, which is the uptake of water and nutrients by plant roots. The combined effect is that increased temperature promotes higher transpiration rates but may hinder efficient absorption by plants.
• Distribution of plants: Temperature plays a vital role in determining the types of vegetation found in specific areas. Different plant species have different temperature requirements for growth and survival. Therefore, the temperature conditions of an area largely influence the composition and distribution of plant communities. For example, certain plant species are adapted to thrive in cold climates, while others are better suited to warmer regions. The temperature range of an area helps define the types of plants that can successfully establish and grow there.

c. Atmospheric Humidity

Atmospheric moisture is in the form of water vapour known as humidity. It is influenced by solar radiation, temperature, altitude and soil water. It plays an important role in the life of plants and animals.

• Higher humidity lower the rate of transpiration and absorption.
• It promotes the germination of spores in fungi and other microbes.
• It promotes the growth of epiphytes and other plants like orchids, those use atmospheric moisture as water for photosynthesis. It is also used by moss and lichens.
• Activities of animals diminished below and above the optimum humidity range.

d. Wind (Air)

Air is a complex mixture of many gas like N2, O2, CO2, and other gases. The moving air from high pressure area to low pressure area is known as wind. The pressure differences are mainly due to differential heating of atmosphere. It shows both physical (Mechanical) and physiological effects on living organisms.

• Rate of respiration and absorption of water increases with high velocity of wind while deceases with low velocity of wind.
• It helps in pollination, dispersal of seeds and fruits.
• High velocity (Storm) wind give some adverse effects like deformation, abrasion, breaking and uprooting of plants, dessication, etc. Soil erosion, decreases soil fertility, deposition of sands on plants and animals, salt spray on coastal plants, lodging of plants (falling down of herbaceous plants on ground), dwarfing of plants etc.

e. Precipitation

The moisture falling on area in the form of dew, frost, hail and snow is called Precipitation. Of all the forms of precipitation, the rain is the main source of soil water. Soil water is utilized by plants and animals. Based on water relation plants are divided into hydrophyte, xerophyte and mesophyte. The precipitation affects organisms in several ways like.

• Rainfall promotes the growth and development of plants.
• The amount of annual rainfall determine the types of vegetation of particular area.
• Heavy rainfall in tropical area throughout the year promotes evergreen forest.
• Good rainfall in one or two seasons promotes deciduous forest.
• Moderate rainfall in one or two seasons favors the grassland.
• Low rainfall promotes xerophytic vegetation.
• Running water or high rainfall causes soil erosion and landslide. It decreases soil fertility.
• High snow fall damages growing buds, fruits, flowers and young parts of plants.

f. Fire

Fire is an important factor. Fire is caused by lightening, friction of branches of trees, Volcano and human activities. Fire gives huge loss of forest productivity and loss in life of flora and fauna, if it caught in forest. It is some beneficial also for organism as fired place is suitable for growth of some fungi, bryophytes etc.

• Fire destroys seeds, seedlings, seeds, herbs, shrubs and trees as well as habitat of wild life.
• It destructs the organic matter in soil and decrease soil fertility.
• Fire destructs soil coverage by burning the grasses or herbs. Fire accelerates soil erosion either by wind or water.
• In some plants as in Populus and Epilobium growth is stimulated by fire
• In some plants like Cynodon, Aristida a large number of seeds are produced by stimulation of fire.
• In some grasses and legumes seeds are germinated easily and vigorously only after fire treatment. Some ascomycetes fungi grow in burnt area, such fungi are known as pyrophilous as Pyronema confluens.

B. Edaphic Factors (Soil Factors)

The composition of soil represents edaphic factors. Soil is the upper weathered surface of the earth mixed with organic matters, and in which micro-organisms live and plants grow. It is the important factors which provide nutrition, water and anchorage of plants. Different components of soil and their effects on living organisms are described as :

a. Soil texture

On the basis of the proportions of soil particles mixed in the soil it is classified into different textural groups. Soil texture directly influences soil water, temperature and root penetration. Loam soil is better for plants growth. Sandy soil has less water holding capacity due to high porosity. Silt soils have high water holding capacity but poor aeration.

b. Soil moisture and soil water

Plants absorb a small quantity of rain water and dew, but large quantity from soil water hold by the soil. It is in different forms – gravitational water, capillary water, hygroscopic water, chemically combined water and water vapor. Mainly hygroscopic water attract in soil particles by cohesive and adhesive force of molecules and not easily absorbed by plants. Capillary water is mainly absorbed by root in certain moisture tension because it is the available form of soil water for plants.

c. Soil reaction

Soil reaction influences the growth and distribution of plants. It may be acidic, alkaline or neutral. Acidic soil: It contains the ions of PO4, SO4 and other ions. Growth and development of some acid loving plants influenced by acidic soil like Rhododendron, tomato etc. Alkaline soil: It contains Ca++, Na+, Mg etc. It increases the permeability of root and cell membrane. It is not suitable for plants. Some plants cannot survive in Ca++ rich soil but slightly alkaline soil favors growth of ferns and birch. Most of the plants grow well in neutral soil (7.0pH) and slight acidic soil.

d. Soil Temperature

Soil temperature influences the plant life. Rate of absorption decrease in low temperature and cause chilling injuries to the roots in winter seasons. It is mostly found in sandy soil. Very high temperature causes heat injuries. It increases absorption of water up to certain optimum temperature (below 48°C).

e. Soil nutrient

Organic matter or humus is formed by death and decay of living beings. Humus is the partially decomposed organic matter. Normally inorganic matters are in the forms of Ca++ OH, Na*, PO, etc. These are useful for the growth of plants.

f. Soil atmosphere (air)

In the soil the space left between soil particles are called soil spaces. These spaces contains air(O2) in soil is necessary for growth of underground parts of plants, for the life of micro organism and other soil inhabitants except denitrifying bacteria. It helps in respiration of different organisms and growth of plants. Water logged soil contains low percentage of O2 in soil which harms the life of soil organism.

g. Soil Fertility (Organisms)

Micro organisms increase soil fertility for growth of plants by decaying of dead organic matters. N2 fixing bacteria increase the fertility while some fungi of soil secrete hormones for root growth. But some organisms produce diseases on the plant and show harmful effects. Some useful organisms like BGA (Nostoc, Oscillatoria) and N2 fixing bacteria (Rhizobium) increase soil fertility.

C. Topographic or Physiographic Factors

Topography concerns with physical structure of the earth. Topographic factors influence vegetation due to variation of climatic factors like light, temperature, air pressure, rainfall, soil conditions etc. Main topographic factors are:

a. Altitude (Height of the place)

Higher altitude decreases the temperature and atmospheric pressure but it increases light intensity, velocity of wind, rainfall and humidity. So altitude influences the patterns of vegetation due to variation of climatic factors. Alpine region (4000 m above) contain grass vegetation due to very cold climate.

b. Steepness of slope

Less steepy area is best for plants growth. Very high steepness of land allows rapid flow of rainfall which causes soil erosion, landslide and uprooting of trees. Slopy soil contains less humidity. So Xerophytic vegetation is generally found in high steepy place.

c. Direction of mountain and valley

Sunward direction is suitable for good vegetation because this position achieves high intensity of light for long duration than the opposite sunward direction. In opposite sunward direction of mountain amphibian plants bryophytes (Moss and liverwort), small bushes and broad-leaved plants are found due to high humidity in soil.

II. Biotic Components

The biotic factors include all living beings present in ecosystem. They are producers, consumers and decomposers which interact with each other and maintain ecosystem. They are as follows:

A. Producers

They are autotrophic plants which synthesize organic compounds from inorganic raw materials in the presence of energy, usually derived from the sun (exception-chemosynthetic bacteria). Organic compounds synthesized by the autotrophs or producers serve two purposes body building and liberation of energy during the process of respiration. The energy contained in the organic compounds is in the chemical form. Only producers are able to change radiant energy into chemical form. They are, therefore, also called converters or transducers (Kortnondy, 1969).

All other organisms depend upon the producers for getting their food and the energy contained in it. Producers other than bacteria, also help in maintaining CO2/O2 balance of the atmosphere. They obtain CO2 (released during respiration and burning) from the atmosphere and release O2 during photosynthesis process.

B. Consumers-Macroconsumers

They are also called phagotrophs (phago-to ingest). Consumers are animals which ingest other organisms (organic matter) as food. They are of two main categories, herbivores and carnivores.

a. Herbivores; feed on plants

The herbivores or primary consumers directly feed on plant matters. Herbivores may be small or large. They are found in both terrestrial and aquatic ecosystems. The common large herbivores are rabbits, deer, cattle, goats, horses, etc. Mice, caterpillars, beetles, weevils, birds, etc. are some smaller terrestrial herbivores. Crustaceans and mollusks constitute the major herbivores of the aquatic ecosystem.

Depending upon the nature of the plant part eaten by them, the herbivores are often distinguished into several types-leaf eaters, frugivores (fruit eating), bark feeders, root feeders, wood borers, sucking animals, etc. Herbivory is useful to some plants as browsing and cutting favor their growth. Animals may also help the plants in pollination and dissemination of fruits. In others, herbivory keeps a control on plant population. Thus the herbivorous caterpillar of Cactoblastis cactorum helps in keeping the spread of Opuntia.

b. Carnivores; feed on the flesh of other animals

Secondary consumers or primary carnivores eat the herbivores, e.g., frog, centipedes, small birds, etc. The secondary consumers in turn, are eaten by tertiary consumers and so on. The carnivores which are not further preyed upon, are called top carnivores, e.g., Vulture, Lion, etc.

C. Parasites

They belong to all categories of organisms including viruses. Parasites are heterotrophs. They obtain food directly from other organisms of all trophic levels. Parasites live on hosts for their food. They may also cause diseases. Sometimes, a disease may spread in an epidemic form and destroy the host from a large area. Parasites, therefore, keep the population of other species under check.

D. Scavengers (Detrivores)

They are animals which feed on the dead bodies of other organisms. The Common scavengers or detrivores are insects, beetles, wood boring beetles, termite, worms, crow, vulture etc. Detrivores seem to be essential for quick breakdown of dead bodies of organisms.

E. Decomposers

They include bacteria, actinomycetes and fungi. The decomposers secrete digestive enzymes in the surroundings of the decaying organic matter. The enzyme converts the complex organic substances into simple and soluble compounds. A number of minerals and raw materials are released during the process. The phenomenon is called mineralisation. Some of the simple and soluble compounds are absorbed by the decomposers for their body building and energy liberation.

Both scavengers and decomposers are important organisms for the removal of detritus or dead bodies of organisms. The degree of removal depends upon the climate, type of vegetation, pH, number and kind of detritus feeders. The complete decomposition of organic matter takes two to a few months in tropical regions and 3-5 years in coniferous forests of temperate region (Ovington, 1962).

Detritus feeders may become food for some group of consumers. Thus bacterial decay become food for mosquito larvae. In this way there is never complete mineralisation though complete decomposition can occur.