Functions of an Ecosystem UPSC

Functions of an Ecosystem

The functions of an Ecosystem is broad , vast and very dynamic and it can be studied under 3 heads :-

1. Energy flow

2. Nutrient cycle

3. Ecological Succession

1. Energy flow

Energy is the basic force responsible for all metabolic ac-tivities. The flow of energy from producer to top consum-ers is called energy fl ow which is unidirectional.

The study of Trophic level interaction in an ecosystem gives an idea about the energy flow through the ecosystem.

Energy flows through the trophic levels: from producers to subsequent trophic levels. This energy always flows from lower (producer) to higher (herbivore, carnivore etc.) trophic level. It never flows in the reverse direction that is from carnivores to herbivores to producers.

The trophic level interaction involves three concepts namely:-

1. Food Chain 

2. Food Web 

3. Ecological Pyramids

Food chain : 

▪ A sequence of organisms that feed on one another.it can be grazing food chain (plant> caterpillar > lizard > snake) or detritus food chain (litter > Earthworms > chicken > hawk).

Food Web :

▪ Several interrelated food chains forms food web where all possible transfers of energy and nutrients happens among the organisms.

Ecological Pyramid :

An ecological pyramid is a graphical representation of the relationship between different organisms in an ecosystem. 

Types of Pyramids:

1. Pyramid of Numbers

• A graphic representation of number of individuals per unit area of various trophic levels stepwise with producers forming the base and top carnivores the tip, is called pyramid of numbers. 

• It can upright (Grassland) or inverted (Parasitic foodchain). As it is difficult to count all organisms, pyramid of numbers does not completely represent tropic structure.

2. Pyramid of Biomass:

• The amount of living or organic matter present in a particular environment is called biomass. 

• A graphic representation of total dry weight of all organisms at each trophic level at a particular time.

• It can be upright (Eco-system on land) or inverted (Aquatic ecosystems).

3. Pyramid of Energy:

• A graphic representation of the amount of energy trapped per unit time and area in different trophic levels of a food chain.

• It is always upright as there will be loss of energy from one trophic to next trophic level.

2. Nutrient Cycle

▪ The cyclic flow of nutrients between the biotic and abiotic components is known as nutrient cycle (or) biogeochemical cycles.

▪ The nutrients enter into producers and move through the food chain and ultimately reach the consumer. 

The bound nutrients of the consumers, after death, are decomposed and converted into inorganic substances, which are readily used up by the plants (producers) and again the cycle starts.

▪ The major nutrients like C, H, O, and N are cycled again and again between biotic and abiotic components of the ecosystem.

Gaseous Cycle

1. Hydrological Cycle

▪ Movement of water in a cyclical manner is known as hydrological cycle.

▪ The hydrologic cycle begins with the evaporation of water from the surface of the ocean. As moist air is lifted, it cools and water vapour condenses to form clouds. Moisture is transported around the globe until it returns to the surface as precipitation.

2. Carbon Cycle

Taking Carbon out of the Atmosphere:

▪ Nature is constantly taking carbon out of the atmosphere. These processes are sometimes called carbon sinks.

▪ Photosynthesis - Plants use photosynthesis to make energy and grow. They take carbon dioxide (CO2), sunlight, and water and turn it into oxygen and sugar. 

Large areas of plants like the rainforest help to remove lots of carbon from the atmosphere.

▪ The ocean - Ocean water does a lot to remove excess carbon from the atmosphere. Carbon dioxide in the air reacts with the sea water to make carbonic acid in the ocean. If there is too much carbonic acid, it may lead to acid rain. However, some carbonic acid is good as it is used by sea organisms to make their shells. These shells will eventually become sedimentary rock like limestone.

Moving Carbon into the Atmosphere:

▪ At the same time that some processes of nature are removing carbon from the air, other processes are adding more carbon to the air. These processes are called sources.

▪ Decay - When plants and animals die they decay. When this happens, the carbon in their body will either be released into the atmosphere or stored in ground as fossil fuels.

▪ Respiration (breathing) - Every time you breathe you turn oxygen into carbon dioxide. This is true of every animal on Earth.

▪ Combustion (burning) - When plants, trees, or fossil fuels are burned, carbon is released into the atmosphere.

3. Nitrogen Cycle

Why is nitrogen important to life?

Plants and animals could not live without nitrogen. It is an important part of many cells and processes such as amino acids, proteins, and even our DNA. It is also needed to make chlorophyll in plants, which plants use in photosynthesis to make their food and energy.

Processes in the Nitrogen Cycle:

▪ Fixation - Fixation is the first step in the process of making nitrogen usable by plants. Here bacteria change nitrogen into ammonium.

▪ Nitrification - This is the process by which ammonium gets changed into nitrates by bacteria. Nitrates are what the plants can then absorb.

▪ Assimilation - This is how plants get nitrogen. They absorb nitrates from the soil into their roots. Then the nitrogen gets used in amino acids, nucleic acids, and chlorophyll.

▪ Ammonification - This is part of the decaying process. When a plant or animal dies, decomposers like fungi and bacteria turn the nitrogen back into ammonium so it can re-enter the nitrogen cycle.

▪ De-nitrification - Extra nitrogen in the soil gets put back out into the air. There are special bacteria that perform this task as well.

Sedimentary Cycle

1. Sulphur Cycle

Sulphur (S) is an element important to ecosystems and the climate. The majority of sulphur is stored underground, for example under the ocean or in rocks. It also occurs naturally in places like swamps (where organisms have decomposed) and volcanoes.

Humans add excess sulphur into this cycle, usually through atmospheric pollution caused by fossil fuel combustion.

Steps of the Sulphur Cycle:

▪ As rocks are worn down by erosion they release sulphur that was once stored, becoming Sulphate once it touches the air.

▪ Plants absorb this sulphur through photosynthesis and make this sulphur organic.

▪ Animals, specifically herbivores and omnivores consume the sulphur when they eat the plants.

▪ Sulphur moves through the food chain as secondary consumers and tertiary consumers eat the primary consumers.

▪ When animals and plants die, the sulphur dissipates into the atmosphere as sulphate and also through the body of the decomposers.

▪ The sulphur in the atmosphere is returned to the soil and water cycle when it rains. Fig: The Sulphur Cycle

2. Phosphorus Cycle

▪ Phosphorus is an essential nutrient for animals and plants. It plays a critical role in cell development and is a key component of molecules that store energy, such as ATP (adenosine tri-phosphate), DNA and lipids (fats and oils). Insufficient phosphorus in the soil can result in a decreased crop yield.

▪ Here are the key steps of the phosphorus cycle,

• Over time, rain and weathering cause rocks to release phosphate ions and other minerals.

• This inorganic phosphate is then distributed in soils and water.

• Plants take up inorganic phosphate from the soil. The plants may then be consumed by animals. Once in the plant or animal, the phosphate is incorporated into organic molecules such as DNA. When the plant or animal dies, it decays, and the organic phosphate is returned to the soil.

• Within the soil, organic forms of phosphate can be made available to plants by bacteria that break down organic matter to inorganic forms of phosphorus. This process is known as mineralisation.

• Phosphorus in soil can end up in waterways and eventually oceans. Once there, it can be incorporated into sediments over time.

3. Ecological Succession

Succession is a universal process of Directional change in vegetation, on an ecological time scale which leads to the establishment of a relatively stable climax community.

Stages of Ecological Succession:

Pioneer Community:

▪ The first group of organism which establish their community in the area is called ‘Pioneer’ Community.

Ex: Lichen, Moss and Microbes 

Seral Stage:

▪ The various developmental stage of a community is called ‘seres’.

▪ Herbs and Shrubs usually grow after further weathering, increase in moisture and soil.

Climax Community:

▪ The final stage of succession which leads to stable community.

Types of Succession:

Primary Succession:

It involves the gradual establishment of biotic communities on a lifeless ground.

Secondary Succession:

It involves the establishment of biotic communities in an area, where some type of biotic community is already present.

Autogenic Succession 

Succession brought about by living inhabitants of that community itself.

Allogenic Succession

Succession brought about by outside forces.

Autotrophic Succession

Succession in which initially green plants are much greater in quantity.

Heterotrophic Succession

Succession in which heterotrophs are much greater in number.