Ecosystem Referral

Ecosystem Referral : Guide

The term ecosystem was coined by A G Tansley (1935). The word ecosystem is derived from eco + system (oikos, meaning home, and systema, or system) where 'eco' depicts the biotic and abiotic components of nature and 'system' means the dynamic functional attributes.

Ecosystem is a basic functional unit of nature which consists of living and non-living factors interacting with each other so that the flow of energy leads to a clearly defined trophic structure, biotic diversity and exchange of materials in the environment.

Structure of Ecosystem

The function of ecosystem involves the volume and the rate at which material circulates and energy flows through the ecosystem.

Nutrient Cycling

Nutrient cycling is one of the most important processes that occur in an ecosystem. The nutrient cycle describes the use, movement, and recycling of nutrients in the environment. Valuable elements such as C, O, H, P, N are essential to life and must be recycled in order for organisms to exist.  


Nutrient cycles are inclusive of both living and non-living components and involve biological, geological, and chemical processes. These nutrient cycles are also known as biogeochemical cycles. They can be of two types: 



Gaseous Cycle: C, O, H, N

Sedimentary Cycle: S, P

Food Chains and Food Webs

Food Chains

The transfer of energy from the sun gets assimilated into the plants through photosynthesis by converting the inorganic raw material into organic matter. This organic matter is passed from producers (like green plants) through a series of organisms with repeated cycles of 'eating and being eaten' by the consumers. This ecological process is termed as a food chain.

Grazing Food Chain

It starts from the plants, and then includes herbivores and carnivores. Such a type of food chain depends upon the influx of the solar radiation.

Grass => Grasshopper => Frog => Snake => Hawk

Detritus Food Chain

It starts from the dead and decaying matter with the help of microorganisms and then into detritus-feeding organisms and their predators. This food chain is not directly dependent on the sun.



Dead Matter => Detritivore (Insect) => Bacteria / Fungi

Food Webs

The interlocking pattern of food chains in a given ecosystem is termed as a food web.

Ecological Pyramids

The graphical representation of trophic levels of different organisms based on their ecological position is referred to as an ecological pyramid. The pyramid consists of a number of horizontal bars depicting specific trophic levels. The length of each bar represents the total number of individuals or biomass or energy at each trophic level in an ecosystem depending upon the type of ecological pyramid. The concept of ecological pyramids was first proposed by an English ecologist Charles Elton. These can be upright or inverted depending upon the type of pyramid and ecosystem.

Pyramid of Energy

It always shows an upright condition for any given ecosystem. Energy of an ecosystem is often expressed in kJ/m2/year. The energy contained in the biomass at each trophic level decreases by 90% at each successive step as the energy acquired by an organism cannot be fully transferred to the higher trophic levels. This is a reflection of the second law of thermodynamics.

Pyramid of Numbers

It shows the number of individuals at each trophic level. It maybe upright or inverted. In this pyramid, the number of organisms in each trophic level is considered as a level in the pyramid. The pyramid of numbers is usually upright except for some situations like that of the detritus food chain, where many organisms feed on one dead plant or animal. For a pond or grassland ecosystem, the pyramid of numbers is upright as the number of consumers is far lesser than the  number of producers. On the other hand, for a forest or tree ecosystem, such an ecological pyramid is usually inverted as a single tree may harbour many consumers.

Pyramid of Biomass

The amount of organic matter (dry weight) that can be found in any living organism is called biomass. It represents the total biomass of organisms at each trophic level in an ecosystem at any given time. It may be inverted or upright. For grassland and forest ecosystems, this type of pyramid is upright as the dry weight of producers is far greater than the consumers. However, for a pond ecosystem, it is inverted as the dry weight of the producers in the pond is far lesser than the fauna present in the ecosystem.

Productivity

Productivity of an ecosystem refers to the rate of production of organic material from inorganic components i.e. total amount of organic matter accumulated in any one unit time. It can be observed at 3 levels: Primary Productivity, Secondary Productivity and Net Productivity. 

Primary Productivity

The rate at which radiant energy is stored in the producers by the process of photosynthesis and chemosynthesis is called primary productivity. It is further divided into two types:

Net Primary Productivity

It is defined as the total rate of photosynthesis which excludes the organic matter used up in the process of respiration during the measurement period

Gross Primary Productivity

It is defined as the rate of storage of organic matter in excess of respiratory utilization by plants during the measurement period.



NPP = GPP – R


Secondary Productivity

It is defined as the productivity or rate of energy storage at the consumer level.

Net Productivity

Net productivity refers to the rate of storage of organic matter not used by the heterotrophs (consumer) during the unit period. It is thus the rate of increase of biomass of the primary producers, which has been left over by the consumers.

Ecological Succession

Succession is defined as the appearance, in an orderly sequence, of different communities over a period of time in the given area. It is an assemblage of interacting populations occupying the area. It begins with a small pioneer species entering a new area which reaches to the climax stage through various intermediate stages called seral stages or seral communities or seres. area.

Types of Succession

Primary Succession

Primary Succession is the process of species colonization and replacement in which the environment is initially virtually free of life. In the other words the process starts with base rose or sand dune or river delta or glacial debris and it ends when climax is reached. The sere involved in primary succession is called presere.

Secondary Succession

Secondary succession is the process of change that occurs after an ecosystem is disrupted but not totally obliterated. In this situation, organic matter and some organisms from the original community will remain; thus the successional process does not start from scratch. As a result, secondary succession is more rapid than primary. It is seen in areas burned by fire or cut by farmers for cultivation. The sere involved in secondary succession is called subsere.

Classification on the basis of Energy and Nutrition

Autotrophic Succession

In this type of succession, the rate of production is always greater than the rate of respiration. Initially, primary producers are present in majority

Heterotrophic Succession

The rate of respiration is greater than the rate of production during the initial phase of hetero-trophic succession. The number of heterotrophic animals are more than producers in the early stages of this type of succession.

Classification on the basis of Colonization

Primary Succession

It occurs in the area where environmental conditions are elementary and that area is occupied for the first time by few simple living organisms.

Secondary Succession

It occurs in the area which was occupied earlier by some type of community. The area which is under the process of colonization in this type of succession had been devastated by natural factors like forest fires, floods, or due to some other disaster and then after a period of several years, that area is again occupied by some community.

Classification on the basis of Interactions

Autogenic Succession 

In most cases, the community is formed during the process of early succession in an given area when it reacts to the environment and thus modifies the environment and results in the replacement of its own community by some new modified community.


Autogenic community is the succession progressing entirely as a result of interactions of the organisms and their environment (i.e. 'driving force' is internal to the community), for instance, succession on sand dunes.

Allogenic Succession

In some cases, one community is replaced by another community due to some other external factors rather than due to the effect of the community on the environment. This is called allogenic succession and it may occur in a highly disturbed area. For instance, succession in a small pond.

Xerarch Succession 

The succession when starts in xeric or dry habitat having minimum amounts of moisture, such as dry deserts, rocks, etc. is called xerach. A temporary community in an ecological succession on dry as sterile habitat is called xerosere. 

Crustose Lichen Stage

It starts on a bare rock on which no life exists on primarily. Initially, the rock is large and solid, and thus, provides no space for rooted trees to grow. The first stage that gets established in the area is called the pioneer stage and includes species of lichen like Rhizocarpan and Rhinodina. They have web-like structures that adhere to the surface of rocks and help to absorb moisture from the surrounding environment. The lichen produces acids which corrode the rock and help in the genesis of soil. They trap soil particles from the wind which also contributes to the soil formation. Dead materials of this stage forms the humus that gets mixed with the soil and provides substratum for the next stage.

Foliose Lichen Stage 

Leafy lichens like Dermatocarpan and Parmelia grow in this stage. They do not allow light to reach the crustose lichen, which causes death of those lichens. The foliose lichen accumulate more soil particles and water from air and help to form soil.

Moss Stage

At this stage, mosses grow as a new community and they mask the growth of foliose lichen. Soil formation continues further from dust and dead, decomposed matter of mosses. Water content of soil increases due to the formation of a sufficiently thick layer of soil.

Herb Stage 

Due to increase in the water content of humus and minerals in the soil, herbs like grasses start growing in the area. Later, biennial and perennial plants also grow.

Shrub Stage

At this stage, quality and quantity of humus and soil moisture increases further and shrubs start growing. The shrub modifies the habitat and dead remains of shrub decompose to enrich the soil by contributing to the humus. The water holding capacity of soil increases which favours the growth of trees.

Forest or Climax Stage

The succession terminates in the climax community, that is, the forest. The forest type depends upon the climatic conditions.

Hydrarch Succession

The succession when starts in the aquatic environment such as ponds, lakes, streams, swamps, bogs, etc. is called hydrach or hydrosere.



Phytoplankton

Submerged plant stage

Submerged free floating

plant stage

Reed-swamp stage

Marsh-meadow stage

Scrub stage

Forest

Phytoplankton Stage 

In the initial stage of succession, bacterial and algal spores are brought into the water body. The simple forms of life like bacteria, algae and many other aquatic phytoplankton and zooplankton floating in water are the pioneer colonizers.


These organisms add large amount of organic matter and nutrients due to their various life activities and after their death, they settle at the bottom of the water body to form a layer of muck.

Submerged Stage 

The phytoplankton stage is followed by submerged plant stage. When a loose layer of mud is formed on the bottom of the pond, some rooted submerged hydrophytes begin to appear on the new substratum. The submerged aquatic vegetation develops in the regions of ponds or lakes where water depth is about 6 – 8 feet or more. The pioneers are Elodia, Potamogeton, Myriophyllum, Ranunculus, Utricularia, Ceratophyllum, Vallisneria, Chara, etc.


These plants form tangled mass and have marked effects upon the habitat. When these plants die their remains are deposited at the bottom of the ponds or lakes. The eroded soil particles and other transported materials are also deposited at the bottom. This gradually raises the ho t the ponds and lakes up. As this process of stratification progresses the body of water becomes more and more shallow, consequently the habitat becomes less suited for the submerged vegetation but more favourable for other plants.

Floating Stage

When the depth of water reaches about 6 – 4 feet, the submerged vegetation starts disappearing from its original place and then the floating plants make their appearance gradually in that area. In the beginning the submerged and floating plants grow intermingled but in the course of time the submerged plants are replaced completely. The most tolerant species in the area are able to reproduce and perpetuate. Their broad leaves floating on the water surface check the penetration of light to deeper layer of water.


This may be one of the main causes responsible for the death of submerged plants. Due to continuous interaction between plant communities and aquatic environment, the habitat becomes changed chemically as well as physically. More water and air borne soil and dead remains of plants are deposited at the bottom. Thus, the substratum rises up in vertical direction. Important floating plants that replace the submerged vegetation are Nelumbo, Trapa, Pistia, Nymphaea, and Limnanthemum etc.

Reed-Swamp Stage

When the ponds and lakes become too shallow (1 – 4 feet) and the habitat is changed so much that it becomes less suited to the floating plants some other plants which are well adapted to new environment will then come in. Under these conditions, the floating plants start disappearing gradually and their places are occupied by amphibious plants which can live successfully in aquatic as well as aerial environment. Important examples are Bothrioclova, Typha, Phragmites (Reed), etc.


The foliage leaves of such plants are exposed much above the surface of water and roots are generally found either in mud or submerged in water. The foliage leaves form a cover over submerged and floating plants and thus they cut off light from the plants underneath them. Under such conditions neither submerged nor floating plants can survive. Further deposition of soil and plant debris at the bottom reduces the depth of water and makes the habitat less suitable for the pre-existing plants.


When the bottom reaches very close to the water surface many secondary species, such as Polygonum, Sagittaria, etc. make their appearance. Later, they also bring about such reactions by which the habitat becomes less suitable for most of the existing species, and consequently new successional step follows.

Marsh-Meadow Stage

The filling process finally results in a marshy soil which may be too dry for the plants of pre-existing community. Now the plants well adapted to new habitat begin to appear in the pre-existing community in mixed state. Important plants that are well suited to marshy habitat are the members of Cyperaceae and Grammeae. The species of sedge (Carex) and rushes (Juncus), species of Themeda, Iris, Dichanthium, Eriophorum, Cymbopogon, Campanula, Mentha, Caltha, Gallium, Teucrium, Cicuta, etc. are the first invaders of marshy area.



As these plants grow most luxuriantly in the marshes, they modify the habitats in several ways. They absorb and transpire a large quantity of water and also catch and accumulate plant debris and wind and water borne soil particles. Consequently a dry habitat results which may be totally unfit for the growth of normal hydrophytes. Gradually the mesophytes start appearing and after some time the sedge vegetation is totally replaced by them.

Scrub Stage

In the beginning some shrubs and later medium sized trees form scrub vegetation. These plants produce more shade and absorb and transpire large quantity of water. Thus, they render the habitat more dry. Shade-loving herbs may also grow under the trees and shrubs. The prominent plants of the scrub community are species of Buteazon, Acacia, Cassia, Terminalia, Salix, etc.

Climax Stage

After a very long time the hydrosere may lead to the development of climax vegetation. As the level of soil is raised much above the water level by progressive accumulation of humus and soil particles, the habitat becomes more dry and certainly well aerated. In such a habitat, well adapted self-maintaining and self-reproducing, nearly stable and uniform plant community consisting mostly of woody trees develops in the form of mesophytic forest.

Forest Ecosystem

The forest ecosystem covers nearly 40% of the land in the world. In India, it is estimated that only 10% land is occupied by forests. The different components of the forest ecosystem are as follows:

Abiotic Components 

The abiotic conditions decide the type of forest ecosystem. The forest ecosystems present in mountainous regions vary greatly from those in the plain regions. Various abiotic conditions like temperature, soil type, pH and rainfall decide the type of vegetation.

Biotic Components

Producers 


Plants like Eucalyptus, Mango, Pinus, Ficus, Teak, Sal, Oak and Conifers are found in forests.


Consumers



Primary, Secondary and Tertiary Consumers are found (give examples)


Decomposers

Bacteria and Fungi

Pond Ecosystem

Pond is the simplest freshwater ecosystem which is self-sufficient and self-regulating in nature. Generally, small ponds dry during the summer season and recover again during monsoon. A pond ecosystem consists of the following components.

Abiotic Components

Minerals like nitrogen, oxygen, carbon dioxide, calcium are dissolved in water that constitute the major abiotic component. Other factors like heat, temperature, pH are also important for the pond ecosystem. 

Biotic Components

Producers

  Typha, Azolla, Hydrilla, Utricularia, Nelumbo, algae etc. are examples of pond producers. 


Consumers 

Fishes, frogs, snakes and crabs are found (give examples) 


Decomposers

Bacteria and Fungi

Grassland Ecosystem

The grassland ecosystem roughly constitutes 19% of the Earth's surface. It has a wide range of vegetation consisting of grasses and small annual plants. Grassland ecosystems receive low rainfall and soil depth as well as quality is poor. Therefore, it restricts the development of large number of trees and shrubs but is enough to sustain the growth of grass cover. The different components of a grassland ecosystem are as follows:

Abiotic Components

Elements like C, N, P, S, O and H are made available to the organisms by carbon dioxide, nitrates, phosphates and sulphates present in the soil along with water available in the environment.

Biotic Components

Producers 

Grasses like Cyanodon, Sporobolus, Dichanthium, Setaria grow in the grasslands.

Consumers

Grasshoppers, rabbits, hares, zebra, centipedes, millipedes, snakes, frogs and birds are found in grasslands (give more examples) 


Decomposers

Bacteria and fungi are the chief decomposers. Fungus species include Aspergillus, Penicillium, Mucor, etc. They decompose complex organic matter into simpler forms which are used by plants to produce biomass. Bacteria include vibrio, bacillus, cocci, and spirillum forms.

Desert Ecosystem

The arid or semi-arid zones in India cover 38.8% of India's geographical area and spread over 10 states. The Indian desert fauna is extremely rich in species diversity of mammals and winter migratory birds. The different components of a desert ecosystem are as follows:

Abiotic Components

It occupies approximately 17% of the total landmass of the planet. Desert ecosystem receives only 20-50 cm of rainfall per year. It makes this ecosystem less productive and because of the scarcity of water, diversity of plants and animals is very low.

Biotic Components

Producers

Plants like Jivanti, milkweed, Euphorbia, indigo, Sodi, Khejri etc. are found in deserts.


Consumers

Desert ecosystems are a habitat for desert cats, desert rats, rattle snakes, camels, desert foxes (lot more examples)

Thanks for reading :)