What is an Ecosystem? Definition, Types, Structure, Components, Importance

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What is an Ecosystem

Think about the lake, you will imagine about a waterbody, think about desert, you will imagine a sand dune with scattered vegetation. Likewise, if you will think about forest, the landscape image of tree dominated landscape will appear in mind. Seeds cannot grow until and unless the presence of moisture. Moreover, sapling is not able to proliferate into a tree without availability of sunlight, water nutrients etc. Plant and animal are living beings but totally dependent directly or indirectly to abiotic factors e.g. the opening of leaves stomata is depend on presence of sunlight. Likewise, the formation of vitamin A, D in human body and carotene in tomato is also dependent to the presence of sunlight.

The elevation and temperature have crucial role in plant distribution e.g. alpine forest (3600-4000 m) and timberline (4000 m) is the outcome of elevation. The survival of plant and animal without its non-living surrounding is not possible. Both living and non-living factors are essential component, intermingled closely and form together an ecosystem. As you know, the earth encompasses the living and non-living entities that interact each other. The utility of the nonliving surroundings is to supply the shelter, nutrient and energy to the inhibiting living organism. As a source for nutrient, shelter and energy the abiotic component is called as ecotype. Summarily ecosystem is biotic component with its ecotype. 

Man and Biosphere 
Nature incorporates itself infinite numbers of creatures within & between several direct & indirect linkages. Human is also one entity of the nature evolve continuously. The existence and progress of human depend upon understanding the diverse linkages of environment and creating equilibrium (i.e. homeostasis). At present the human has pulled over the destructive transformation in name of civilization with a huge negligence of nature behavior and intervention. Most of the creation of man for comfort and pleasure has sit on volcano. In current era, 91% of global human inhabitants live in pollution zone (WHO, 2018) and are facing death and detrimental effects of pollution. The unparallel leverage of population and negligence to role of environment are root cause to destructive unsustainable development. The need to understand the environment, its role and functions are first and foremost liability of human society.
Figure 1: Biosphere and other segments on earth where organism lives.

Atmosphere is the largest chunk of biosphere mainly encompass of gases, droplets and solids. It also acts as a medium for flow of energy in ecosystem, conductive values of biologicals and other materials. The typical behavior of temperature with its co-parameters in plays significant role in climate of ecosystem. The temperature is the deciding factor at different stages of plant growth like seed germination, flowering and fruiting etc. Organisms on the basis of temperature profiling are categorized as psychrophile, mesophile, thermophile, steno- and eury-thermic. The temperature gradient in water body at different depth controls the dissolve oxygen content of water body and regulates the biotic composition of water body. The profiling of temperature is crucial to determine the physiological response of temperature. The interaction of plant behavior and distribution regarding environmental factors are known as physiological response. Likewise, the temperature plays different role in soil and atmosphere. The science of atmosphere is Meteorology and Climatology.

Simply lithosphere denotes to the land masses and land where soil biota exists called as soil. Soil is three-dimension body in contrast to land i.e. 
two-dimensional body. The soil type and properties is crucially essential for the growth of plant, construction of building and other construction like runway for aircraft. The soil type determines through the soil physical properties like texture, structure, B.D., P.D., heat storage effect etc. and thermal property of soil like conductivity, diffusivity, heat flux and mass transfer in soil. The ecosystem is interconnected system and some water related issues are specifically discussed in soil segment as they are so connected with the soil properties e.g. soil water and types, field capacity, water stress and wilting coefficient, saturation of water, water holding capacity and retention, forces on water, water potential, seepage, infiltration, percolation and soil water flow devices. The science of solid earth is called as Geology, science of soil is Pedology and science of landforms is Geomorphology. The tree stands sequester the CO2 and maintain the gaseous exchange and temperature on earths (Bijalwan et al., 2017).

The realm constituting water is called hydrosphere. The water is in 2/3 of the earth but little fraction (1%) only is potable water available and rest of water is with high salt content hence called as marine water and unfit for drinking purpose. Now earth is at alarming state due to dwindling water resource especially in India. Hydrosphere is very essential segment of biosphere as the life can exist only with the water on earth. The science of sea and ocean is Oceanography (Shankhwar et al., 2012). The living beings exist in all the three spheres (atmosphere, lithosphere and hydrosphere) collectively called as biosphere. 

Definition of Ecosystem

Ecological system (ecosystem) is the connection or relation of living and non-living constituents in a physical space (imaginary boundary). As the ecosystem constitute with two factors interconnected to each other namely biotic and abiotic factors. The ecosystem is assemblage of biotic and abiotic resources and associated with the humans since time immemorial in every phase of life. The realm of ecosystem consist the biotic and non-biotic in its complex interactive forms. These two factors organize the ecosystem but their cumulative effects still need to discover. In typical sense, the ecosystem governs with abiotic or environmental condition, distance and proximity with surrounding, and biological interactions. The biological interactions reveal the competition (inter- and intra-specific competition), mutual relationship and trophic levels of biological entity. The interaction and interrelation regulates the nutrient cycles and energy run of system among organism and communities. It is a complex and open system in which the flow of energy and nutrient cycles organize the system in self-regulated, hierarchically and self -organized mode e.g. forest ecosystem, pond ecosystem, desert ecosystem etc. A.G. Tansley in 1935 has given the term ecosystem. He redefined the term as the interactive arrangement of biocenosis (association of living system) and biotope (physical environment).

Structure of Ecosystem

For the better understanding of ecosystem one need to understand the hierarchical levels of organism in nature, prior to the ecosystem, living system starts from elemental level i.e. atom of element (till today 94 naturally occurring elements on earth are known to science) to molecule (the assemblage of two or more than two atoms), and to cell (the assemblage of micro- and macro-molecules to organize a cell).

Hierarchical system of living system in nature
Figure 2: Hierarchical system of living system in nature

The cell also considered as the basic unit of organism and on the basis of cell, the organism may be categories into uni-cellular and multi-cellular organisms. The next level after cell is the organism; population and community are the biotic component of an ecosystem (see the Fig. 2 & 3). 
The assemblage of the organism forms population and two or more than two different populations comprise the community. The biotic component is the integral part of ecosystem and form an ecosystem after inclusion of abiotic component. Basically the ecosystem reflects how the biotic and abiotic component interacts with each other (see the Fig. 2). The ecosystem of same land regime is called the landscape. The large land regimes with same landscape create a biome e.g. Tundra biome, Taiga biome etc. The assemblage of all biome form atmosphere, lithosphere, and hydrosphere is called Biosphere. The abiotic element of environment is so influencing so the name of hierarchical level like ecosystem, landscape and biome is designated behind the abiotic factors.

The biosphere establishes of numerous pockets or patches or ecosystems comprising together biotic constituents with abiotic realms. These ecosystems have their own microenvironments however, all of these ecosystems are interlinked and interdependent and collectively form biosphere.

The abiotic realms broadly consider as environmental factors. The environmental factors are also interconnected to these ecosystems and as per feedback from the interactions of living organisms and their microenvironment, these environmental factors respond to life and microenvironment of the ecosystem.
structure of ecosystem : atom to biosphere level

These interlinking connections in homeostasis balance to interdependent components of ecosystem and responsible for further modifications/alteration of ecosystem too. These interactions are very complex to understand and in matrix form. The two scenarios for better understanding the role of abiotic factor in ecosystem are as follows: In first scenario, after the summer season, when the first rain comes down to ground it simple activate the soil enzymes for intake of the nutrients after converting it into readily available form. The supply of nutrients to the plant makes it greener and enhances the growth. But the nutrients were already present over there into soil and the water makes it available through numerous activities for positive growth.

Moreover, if the rain is for longer time to stagnant water or absence of proper drainage, the water reduces the nutrients present over there and ultimately ill-impact to plant growth. Likewise, in this second scenario impact of rain on seed germination by introducing the rainwater to ecosystem the seed already present over there start to germinate out by the activity of various enzymes in presence of water. If the rain is for longer duration to stagnant water or absence of proper drainage, the water degenerate the seed or germinated root system and ultimately ill-impact to plant growth. Thus the single parameter of environment (i.e. water) has the impact to ecosystem and likewise several other simultaneously impacted on ecosystem at the same time.

However, prior to change in ecosystem various interconnected attributes are changed. Thus the energy and mass transfers in the soil-plant-atmosphere system is govern and interdependent to various abiotic components. For better management of soil-plant atmosphere systems, the biophysical methods and engineering process need to be understood in term of soil-plant interactions. The soil-plant interaction in reference to plant growth is dependent to the abiotic components like water, heat and gas flows, energy budgets and nutrient dynamics etc. 

Components of Ecosystem 

Across the hierarchical levels all the components may group into the following living (biotic) and non-living (abiotic) components. However, the ecosystem functioning require energy for different vital activities. The ecosystem constitutes two main constituents biotic and abiotic components along with energy. The living or biotic component further categorized into producer, consumer and decomposers (Fig 4).
Components of Ecosystem
The producer are chlorophyllous plants, they produce the food through the photosynthesis activity, hence called producer. The consumer is living organism who depends on the producer for their food. The consumers are further categorized into primary, secondary and tertiary consumers in hierarchical level in different food chains and food webs. The living organism grows with the various interactions in their environment and completes their life. When they die, they attract some micro-organisms (bacteria, fungi etc.) to break down the body of dead organism and decompose it to the soil. Thus the lives in ecosystem start from the producer and the food and energy transfer to consumer and after death the organism decompose to the soil and energy release to the environment. The ultimate source of energy on earth is Sun; producers during the process of photosynthesis utilize this radiant energy and transfer to the ecosystem as per hierarchical levels. Thus the whole system is interconnected and interdependent for food, energy and water & nutrient cycling in ecosystem. The system is complex and invariably changes with the varying components of the ecosystem. 

Characteristics of Ecosystem 

As earlier discussed, the ecosystem is complex and invariably changes in changing environmental factors. Hence, it is difficult to define the ecosystem characteristic in single line. The ecosystem characteristics are as follows: 
  • It is a structurally (living and nonliving) and functionally organized (actively transfer of food, energy in hierarchy) system 
  • Ecological system is the interrelated and interdependent dynamic system, the dynamic activity results the natural resources and includes all of its natural resources in to ecosystem 
  • The vital activity of ecosystem fueled by the radiant energy of sun and the transfer of energy in to the trophic levels results to the productivity of ecosystem 
  • The ultimate source of energy on earth is sun, and the flow of energy in ecosystem is uni-directional, however, different types of ecosystem run through the existing energy movement 
  • The interconnectivity and interactions of ecosystem made it an open system with continuous input and output of mass and energy

Types of Ecosystems 

The realm altogether with its all resources is considered as ecosystem. Mainly the ecosystem is categorized into natural and man-made ecosystem. In current era, none of the ecosystem is inaccessible to human interruptions. However, for study purpose the ecosystem is grouped into different ecosystem types as follows: 
Types of Ecosystem
Figure 5 Types of Ecosystems

Table 1: Description about Biome/Ecosystem

The hierarchical level of an ecosystem starts from organism at basic level and after several levels attains the biosphere at highest level. The biosphere is the ultimate ecosystem on the earth and confines all the biological entity with its non-biotic constituent altogether. Mostly ecosystems are natural but manmade ecosystem also exist in nature e.g. Agroecosystem, aquarium etc.

Man-made Ecosystem 
The human involvement and intervention have changed or modified the ecosystem at great extent as per their requirement and utilization of the ecosystem. The result of this excessive influence has turned out the ecosystem, so they considered as man-made ecosystem or artificial ecosystem e.g. cropland, aquarium, arboretum, lawn, waterpark etc.

Natural Ecosystem
The forest ecosystem is one of the most diverse ecosystems. Indian forests are classified into six major groups namely Moist Tropical, Dry Tropical, Montane Sub-tropical, Montane Temperate, Sub Alpine and Alpine Scrub Forest. 

Importance of Ecosystem

The ecosystem has a leading role in nature. Its significance can be study under the categories of Ecosystem services and Revenue generation. 

Ecosystem Services (ES)
A number of human derived benefits (HDBs) obtained from the environment/nature/ecosystem directly or indirectly, knowingly or unknowingly and these human-derived benefits are called as ecosystem services (ES). These HDBs may be due to the function, positioning, characteristics, and/or processes of ecological-system and in pertinent to the necessity of human-being for their facility, comfort and wellbeing. Ultimately the term ES denotes to HDB from the ecosystem. These HBDs may further categorized under provisioning, regulating, cultural and supporting services. Any HDBs obtained from the ecosystem naturally may be considered as ES and enlisted in Fig 6. 

Revenue generation from ES
All the natural resource on earth confine in pockets called ecosystems. Ecosystem is the ultimate source of all revenue, and it satisfies the human demands since immemorial time. The ecosystem services are exchanged in form of revenue or monitory term as per the human need and resource availability. 

Flow of energy 
The two components of ecosystem are also dependent to sunlight for the energy. The energy move from the ultimate source of energy (sun) to the producers (green plants) in form of small pockets (quanta). The green plants accomplish the photosynthetic activity by the virtue of chlorophylls presence. The photosynthetic activity is the entry point of energy flow to biotic community and energy transfer from producer to consumer and ultimately to decomposers. The energy flow universally follows this pattern of energy flow and hence, it is called as unidirectional flow of energy. 

Nutrient cycling 
The flow of energy into ecosystem ensures the growth of biotic community at different hierarchical levels. After the maturity time the plant and animal got death and decay and shred down to ecosystem and finally decompose out by the activity of tiny microbes. The small microbes help to disintegrating the dead body of animals and plants releases nutrients back to the soil (ecosystem).
Thus, the nutrient flow in different segments of ecosystem and this flow are called as nutrient cycling. 

Himalayan forest of Uttarakhand 
The forest of Central Himalaya in Uttarakhand region is stretched from Tarai, bhabhar at lower elevation approximately less than 300m. The upper hill of Uttarakhand Forest attains up to 2800-3400 m elevation. The forest is rich in biodiversity and changes with the elevation situated characteristically considered as tropical, sub-tropical, temperate, cold and frigid (winter).
Fig 6: Ecosystem Services

In the Tarai region the Sal, Shisham, Teak and Mahogany trees are dominating, the valley region comprises broad leaf deciduous forest and grass patch are also available in this region. In the mid altitude the main tree species of Oak, Banj, Buransh, and Kafal along with Chirpine exist in this region and Uttarakhand Forest are known for this species. In high hill region the coniferous tree species like deodar, spruce and fir are found dominantly (Shankhwar et al., 2020). Afterward in alpine meadows only some medicinal and wild plants exist which freeze out in winter seasons.

CO2 fertilization in forest ecosystem and carbon sequestration
The forest area decided to cover at least the 33% to its geographical area the hilly terrain is fragile in nature hence for conservation strategy, forest area in hilly terrain is decided to 66% of geographical area. India is rich in biodiversity due to its geographic diversity from Himalaya to desert area of Rajasthan. Indian Himalaya is enriched with biodiversity and forest resources. Locally the Himalayan ecosystem supplies the fuel, fodder, timber, clean water, and hydroelectricity but globally it contributes to the carbon sequestration and hydrological cycles.

Concepts in Ecology

The emergent property principle
The ecosystem is a hierarchical set-up of distinctly different levels. Each level has its own characteristics feature that is the outcome of that particular level in hierarchy and it has no existence without hierarchy. The characteristics are emerging out due to that particular level, so it called as emergent property. The emergent property describes the factors that cannot be explained individually, as intermingled with numerous factors.

A state of balance in an ecosystem is called homeostasis. The homeostasis is like a balance of two factors of promotion and reduction. E.g. plant in a pot drying due to absence of irrigation water will dry up gradually. However, the over constant irrigation to that plant-pot will lead to rotting down of the plant. In between two situations, another situation of controlled irrigation will flourish the growth of plant in pot. Here the balanced irrigation reveals one of example of homeostasis. The unavailability of irrigation water to pot results to wilting before drying up is a sort of negative feedback. The negative feedback is like a warning system that helps to balance the ecosystem through feedback mechanisms.

Gaia hypothesis
The temperature and rainfall influence the climate, agriculture and ultimately the human life in many ways. However, it is very important to understand that the ecosystem is solely coexistence of biotic and abiotic factors and biotic factor also responsible to regulate/change the environment (abiotic). We may consider all living being as biotic factor that interdependent to its environment (abiotic factor). These biotic factors also influence/regulate/change its environment. James Lovelock proposed in Gaia hypothesis that the biosphere is as self-regulating system and biotic component regulate to its abiotic factor (environment).

Example: The exploding human population exerts the higher concentration of CO2 that ultimately climate change (the global problem) a threat to human society. The most drastic threat to human being is depleting water resource is also the outcome of increasing population and mismanagement of human. In Precambrian age, the photosynthetic bacteria also influence the global environment and evolved the environment to aerobic.

Cybernetics and Stability

The ecosystem is so interconnected and interdependent that the sequential events are also controlled by previous step, or the primary steps have the controlling power to final step.
This complex interconnection and inter-dependence are sum to cybernetics e.g. in a grassland if grasses grow more, it can feed more grasshopper and grasshopper will maintain the grass abundance. More growth of grasshopper population attract frog who feed on grasshopper and frog population will control the population of grasshopper. Likewise, the frog population is controlled by the snake. Thus, ultimately, the population of snake in grassland is dependent on grass indirectly (Grass → Grasshopper → Frog → Snake). The increasing number of snakes leading to decreasing number of frog and if lesser numbers of frog, then higher number of grasshoppers that lead high infestation on grass. The same concept of cybernetics is also applied in agroecosystem. The agriculture crop is highly affected by the rat. The population of rat can be easily controlled by the snake (Crop → Rat → Snake) and may be concluded that the higher snake population is helpful for agriculture production.

In Grass → Grasshopper → Frog → Snake, the higher growth of grass leads to higher growth of grasshopper too. But after a certain point, the increasing population of grasshopper will diminish the growth of grasses. This limiting of growth of grass, ultimately will limit the growth of grasshopper too, as higher growth of grass promotes the higher growth of grasshopper too. Likewise, in next step, the higher population of grasshopper led to higher growth of frog, but after a certain time the increased population of frog will limit the population of grasshopper by feeding up upon grasshopper. Decreasing population of grasshopper will ultimately result decreased population of frog. Likewise, the leaf litters of tree growing in the soil are recycled back the nutrients to the soil. Thus the nutrients obtained from the soil solution to the tree for their growth and development and leaf litter decomposition returned back the nutrients to soil and hence maintain the stability of the nature (Monika et al., 2017). 
This mechanism of controlling population through feedback is responsible for constant population of organism in an ecosystem after a certain period of time, hence, called as stability through feedback mechanism.

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