Ecosystem; Definition, Meaning and It’s Structural and Functional Aspects

Introduction

An ecosystem refers to a specific area or habitat where living organisms co-exist and interact with each other and with the non-living elements of their environment.

It can also be defined as a biological community of interacting organisms (living, or biotic components) and their physical environment (abiotic components).

The concept of an ecosystem was first introduced by A.G. Tansley in 1935. It is regarded as the fundamental unit of ecology, encompassing both structure and function.

It can be defined as a natural area that includes living organisms (biotic components) and their interactions with the physical environment (abiotic components), enabling the flow of energy and the cycling of nutrients within the system. Simply put, an ecosystem is a distinct and self-sustaining system that supports life, with specific structure and functionality.

Within an ecosystem, there is a continuous flow of energy and cycling of nutrients that support the functioning and sustainability of the system as a whole.

Ecosystems can vary in scale, ranging from small microhabitats to vast biomes, each with its own unique set of organisms and environmental characteristics.

Ecosystem can be explained in two aspects;

• Structural aspect of an ecosystem
• Functional aspect of an ecosystem

Structural Aspect of An Ecosystem

The structure of an ecosystem is chiefly related to the composition of biological community or species diversity (biotic components) and the quantity and distribution of the non-living things (abiotic components). Thus from structural point of view ecosystem consists of following two basic components.

Structural aspect of an ecosystem consist of two components;

• Abiotic Components
• Biotic Components

Abiotic Component of an Ecosystem

These include inorganic and organic compounds of the ecosystem. The inorganic components are carbon-dioxide, water, oxygen, nitrogen, calcium, phosphate etc. all of which are involved in matter cycling (biogeochemical cycles.)

The organic compounds of an ecosystem are proteins, carbohydrates, lipids, amino acids etc, all of which are synthesized by living organisms of an ecosystem and are reached to ecosystem as their wastes, dead remains etc.

The climatic factors ( temperature, light, humidity, atmospheric pressure, fire etc.), edaphic factors (soil texture, soil moisture, soil reaction, soil temperature, soil nutrient, aeriation of soil etc.), topographic factors (altitude, steepness of slope, direction of slope etc.) are other abiotic components of the ecosystem which directly or indirectly influences an ecosystem.

Biotic Components of an Ecosystem

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:

Producers

Producers are autotrophic organisms like photosynthetic bacteria and chemosynthetic bacteria, blue green algae and all other green plants. They are called producers because they capture energy from non-organic sources (solar energy & chemical energy) and store some of the energy in the form of organic food (chemical energy) by photosynthesis process.

Consumers

They are heterotrophic organisms in the ecosystem, which derive their food from other organisms. They are herbivores, carnivores or top carnivores.

• Herbivores: Herbivores obtain food from plants or producers and are called as primary consumers eg. cow, rabbit, grasshopper, zooplanktons etc.
• Carnivores: Carnivores derive their food from herbivores and are called as secondary consumers. eg. fox, jackel, frog, small fishes etc. Sometimes secondary consumers are omnivores which take their food from both primary consumer and producer.
• Top carnivores: Top carnivores derive their food from both primary consumer and secondary consumer and are called as tertiary consumers eg. tiger, lion, hawk etc. Consumers are also known as phagotrophs, because they ingest their organic food matter.

Decomposers

Decomposers are heterotrophic micro-organisms. They are saprophytic organisms that break dead and waste matter and convert complex organic compounds into its simpler and soluble forms. . A number of minerals and raw materials are released during the process. The phenomenon is called mineralization. They include bacteria, actinomycetes and fungi.

Functional Aspect of An Ecosystem

The functional aspects of ecosystem include the flow of energy and the cycling of nutrient matters through. structural components of the ecosystem.

The solar energy captured by green plants is transferred to various levels of consumers (animals) as food energy. Some of this energy is lost as heat during the respiration of organisms. A significant amount of energy is also lost to the environment when the dead bodies of organisms are decomposed by decomposers.

Therefore, in an ecosystem, energy flows in a unidirectional manner among living organisms. Similarly, the inorganic nutrients taken up by producers and consumers are released back into the environment when their dead bodies are decomposed by decomposers.

These inorganic nutrients are then reused by producers and other organisms. Thus, in an ecosystem, nutrient cycling occurs between living organisms and the environment.

Functional aspect of an ecosystem can be explained by following parameters.

• Trophic Level
• Food Chain
• Food Web
• Ecological Pyramid

Trophic Level

There are different aspects or approaches to study the ecosystem which relates organisms to their environment. When we consider organisms, they are interrelated among themselves by eating and being eaten process.

In other words, all organisms in an ecosystem have their feeding relationship. Every organisms need energy to survive, grow and reproduce so that they consume their prey, e.g., carnivores consume herbivores. Organisms are found in different feeding groups or levels of feeding which is called trophic level.

Organisms of similar feeding habit constitute the one trophic level. Examples of trophic levels in the ecosystem are autotrophs, herbivores, carnivores and decomposers. These trophic levels show feeding relationship of organisms in the ecosystem.

Producers are first trophic level (T1). The herbivores which eat plants fall under, second trophic level (T2). Similarly, carnivores which consume herbivores are third trophic level (T3) and so on.

Food Chain

Food chain is defined as the transfer of food energy from the source (producers) through the series of organisms (consumers) in the ecosystem by the continuous process of eating and being eaten. Hence, green plants are always found at base of a food chain.

For example, cereals-plants is eaten by rat, rat is eaten by snake and in turn snake is eaten by hawk. Food chains are basically divided into three types;

• Grazing Food Chain
• Detritus Food Chain
• Parasitic Food Chain

Grazing Food Chain

This type of food chain starts from the living green plants and goes to grazing herbivores and again to carnivores. Thus the base of this food chain consists of living green plants or producers. Other successive levels include herbivores and carnivores.

Such type of food chain depends on the solar energy which is circulated through the food chain. Such type of food chains are more prevalent in nature.

Detritus Food Chain

This type of food chain goes from dead organic matter (detritus) into micro- organisms and then to organisms feeding on detritus (detrivores) and their predators. Thus the base of first trophic level of this kind of food chain is formed by dead organic matter which is then directed towards microorganisms and other detritus feeders.

This food chain doesn’t utilize direct solar energy. Detritus feeders include insect larvae, arthropods, crustaceans, mollusks etc. After this detritus consumer level, the food chain assumes similar pattern to that of grazing food chain

Parasitic Food Chain

This type of food chain chain starts from the parasites feeding on the hosts body. It passes through the hyperparasites and ultimately to the decomposers.

Food Web

In any ecosystem there exist more than one linear food chains. These food chains are interconnected or interrelated with each other and can not be separated.

In nature there are found alternatives and most animals (consumers) have more than one food sources. Sharing of food resources occurs at different trophic levels.

The interlocking pattern of different food chain form a net-like structure known as food web. The complexity of any food web depends upon the diversity of organisms in the system.

Ecological Pyramids

The graphic representation a different trophic structures in an ecosystem is known as ecological pyramid. When energy transfers from one level to another level in a food chain, there is energy loss in each step. This phenomenon gives a definite trophic structure to a particular ecosystem. Such trophic structures can be represented or shown graphically by means of ecological pyramids.

Ecological pyramid indicates the trophic structure and functions of an ecosystem. Ecological pyramid may be upright or inverted. Such pyramids are of different types, viz. pyramids of number, pyramids of energy and pyramids of biomass.

• Pyramid of Number
• Pyramid of Biomass
• Pyramid of Energy

Pyramid of Number

It shows the relationship between producers, herbivores and carnivores at successive trophic levels in terms of their number. It is mainly based on the population density of these trophic levels. The number of individual organisms decrease as we go from 1st trophic level to 2nd trophic level and so on.

This can be illustrated by taking an example of pond ecosystem. The lowest or first trophic level is occupied by Phyto-planktons (producers) which are much abundant. The second trophic level is occupied by zooplanktons (primary consumer) and are less abundant than producer. The third and fourth trophic levels are occupied by small fishes and large fishes respectively. And there is gradual reduction in the number of individual of these trophic levels. Hence, it was found that the number of individuals decrease as we pass from 1st trophic levels to 2nd and so on. It shows upright pyramid. Similar is in the case of forest ecosystem i.e pyramid of number is upright.

But in some cases, when we study on parasites, the pyramid of number may be found in inverted position. This can be explained by giving an example. Many herbivores organisms may live on a single large tree. In this case herbivorous animals outnumber the number of trees. These herbivorous animals may feed upon by many large parasites. These parasites in turn may be parasitized by other parasites called hyperparasites. In this case, the pyramid of number is found in inverted position. It shows inverted pyramid.

Pyramid of Biomass

It shows the relationship between producers, herbivores and carnivores at successive trophic level in terms of their biomass. The pyramid of biomass is determined by calculating biomass of different trophic levels for a given unit area, e.g., biomass of producers, biomass of herbivores and so on.

The pyramids of biomass clearly show that the biomass decreases with the increase in trophic level. For example, in the grassland ecosystem, the producers (grass) occupy the 1st trophic level and the herbivores occupy the 2nd trophic level. Similarly, carnivores and top carnivores occupy the 3rd and 4th trophic levels respectively.

In the grassland ecosystem, the biomass decreases with the increase in trophic level. It shows upright pyramid while in pond ecosystem biomass is decreasing in increasing trophic levels. It shows inverted pyramid.

Pyramid of Energy

It shows the relationship between producers, herbivores and carnivores at successive trophic levels in terms of their available energy. The pyramid of energy of the ecosystem also clearly indicates that the availbility of energy at different trophic level decreases as we go towards increased trophic level.

Producers contain greater amount of energy than herbivores. Similarly, secondary consumer level consists of less amount of energy than primary consumer level. It is considered that the energy when passes from one level to another trophic level, it is lost as heat and by increased respiration rate of higher trophic level. It is always upright in all types of ecosystems.

Productivity of An Ecosystem

Productivity: Productivity is the amount of production of energy containing food which is needed by every organism for their bodily processes. Thus, the rate of storage of energy by green plants with the help of photosynthesis determines the primary productivity of an ecosystem.

Gross Primary Productivity: The total amount of dry matter produced by the plant by photosynthesis is called gross primary productivity. It is calculated as dry weight per unit area per unit time.

Net Primary Productivity: After production of food, plants loss some food when they respire. There is reduction in gross primary production by the reduction of dry weight during respiration. Now, the overall gain of dry weight by the plant after respiration is called net primary productivity.

Hence, gross primary productivity, net primary productivity and loss of dry weight during respiration can be related as follows:

Net primary productivity = Gross primary productivity – Dry weight lost in respiration

Secondary Productivity: The rates of energy storage of consumers level is called secondary productivity.