Chapters :

Ecology & Ecosystem - 01

Learning outcomes

In this unit you will be able to learn the following:

The concept of ecology, ecosystem and its related phenomena.


Our living world is fascinatingly diverse and amazingly complex. Our earth’s life support system consists of four main components – 

  1. The Geosphere
  2.  The atmosphere 
  3. The Hydrosphere
  4.  The Biosphere.

We can try to understand its complexity at various levels of biological organization–Macromolecules, Cells, Tissues, Organs, Individual Organisms, Population, Communities, Ecosystems and Biomes. These communities and its interaction with the environment accounts for the subject matter of study under ecology and environment. 


Ecology is the scientific study of organisms with their surroundings i.e. the physical environment and within themselves. The term ‘Ecology’ was first coined by the German biologist Ernst Haeckel in 1869. Haeckel defined ecology as ‘the study of natural environment including the relations of organisms to one another and to their surroundings.’ It is derived from two Greek words – “oikos” meaning home and “logos” meaning study. Thus literally, ecology is the study of life at home with main emphasis on pattern of relations between organisms and their surrounding environment.

Ecology can also be considered in terms of concept of levels of organization. The entire biological spectrum can at the best be divided into ten levels of organization including Atom, Cell, Organ & Organ System. The ecologists study interactions within and among six of these levels – 

  1. Organisms 
  2. Populations 
  3. Communities 
  4. Ecosystems 
  5. Biomes  
  6. Biosphere.

Levels Of Biological Organization 


Organisms interact with one another and with their environment in a number of ways. These fundamental interactions among organisms and their non-living/physico-chemical environment constitute an interrelating and interdependent ever-changing system known as an ecological system or ecosystem

Therefore ecosystem can be defined as a functional unit of nature, where living organisms interact among themselves and also with the surrounding physical environment. The term ‘Ecosystem’ was first coined in 1935 by the British ecologist Sir Arthur G. Tansley. 


  1. The ecosystem is the major Structural & Functional unit of Ecology
  2. The structure of an ecosystem is related to its Species Diversity; the more complex ecosystems have high species diversity. 
  3. Ecosystems mature by passing from less complex to more complex stages. Early stages of such succession have an excess of potential energy and a relatively high energy flow per unit biomass
  4. Alterations in the environment represent selective pressures upon the population to which it must adjust. Organisms which are unable to adjust to the changed environment disappear ultimately
  5. All ecosystems have a feeding hierarchy which starts with an energy source (e.g. the sun) and then followed by Producers, Consumers & Decomposers. These components are dependent on one another. One of the important features is presence of Grazing Or Detritus Food Chain and Food Webs which become the lifeline of ecosystems. 
  6. Ecosystems are sustained by the presence of biodiversity. Each organism in an ecosystem has a purpose (i.e. niche), as a result, the loss of one species can alter both the size and stability of ecosystems. 


Ecotone is a transitional area of vegetation between two different communities, such as Forest And Grassland. It has some of the characteristics of each bordering biological community and often contains species not found in the overlapping communities. 

An Ecotone often has a higher density of organisms of one and a greater number of species than are found in either adjacent community. Some organisms need a transitional area for activities such as courtship, nesting, or foraging for food. 

Ecotones also appear where one body of water meets another (e.g., Estuaries And Lagoons) or at the boundary between the Water And The Land (e.g., marshes).  Freshwater & Marine Ecotone is characterized by the presence of large plants that rise from roots attached to the submerged substrate, and thus they occur in areas where ample light is available at the bottom of the basin to permit growth.


Abiotic          Biotic 

The ecosystem is largely divided into two components – Abiotic and Biotic components. Ecosystem structure is created due to interaction between Abiotic & Biotic components, varying over space and time.

The structure of ecosystem is composed of the following components:


They mainly include 

  1. Inorganic substances – such as Carbon Dioxide, Water, Nitrogen, Calcium, Phosphorus, etc. that are involved in material cycles. The amount of these inorganic substances present at any given time in ecosystem is called as Standing State Or Standing Quality Of Ecosystem. 
  2. Organic Compounds – Proteins, Carbohydrates, Amino Acids, Lipids, Humic substances and others are synthesized by the biotic counterpart of an ecosystem. They make biochemical structure of ecosystem. 
  3. Climatic FactorsRain, Light, Temperature, Humidity, Wind And Air 
  4. Other factors – such as Minerals, Soil, Topography, Ph, etc. greatly determine the functions, distribution, structure, behavior and inter-relationship of organisms in a habitat. 


The biotic components of the ecosystems living are the organisms including plants, animals and microorganisms. These biotic factors are classified according to their role in the ecosystem as:

  • Producers Or Autotrophs –these are the green plants with chlorophyll which gives them the ability to use solar energy to manufacture their own food using simple inorganic abiotic substances, through the process of photosynthesis.

 For eg. Green Plants, Herbs, Shrubs, Trees, Phytoplanktons, Algae, Mosses, etc. bacteria beneath in the ocean which can synthesize their food in absence of sunlight, thus known as Chemoautotrophs

Consumers or Heterotrophs – It includes 

1. Herbivorous (feed on Plants).

2. Carnivorous (feed on other Animals).

3. Omnivorous (feed on both Plants & Animals) and

4. Detritivores organisms (feed on Dead Parts, Waste, Remains, of plants and animals. 

Decomposers Or Saprotrophs – The Microorganisms, Bacteria & Fungi, which break down complex dead organic matter into simple inorganic forms, absorb some of the decomposition products, and release inorganic nutrients that are reused by the producers.

Therefore all ecosystems have their own set of producers, consumers and decomposers which are specific to that ecosystem. 


All types of ecosystems fall into one of two categories:      Terrestrial Or Aquatic. Terrestrial ecosystems are land based, while aquatic are water based


The distribution of terrestrial ecosystems is primarily related to Precipitation ( Mean Depends on rainfall )and Temperature. Terrestrial ecosystems can be divided, mainly on the basis of the prevailing vegetation type, into three basic categories: 

  • Forest Ecosystem 
  • Grassland Ecosystem  
  • Desert Ecosystem.


Forest ecosystems cover large parts of the terrestrial land surface and are major components of the terrestrial carbon cycle. Trees, the main component of forest ecosystems, contain the largest stock or absolute quantity of the living forest biomass.

Its direct offerings include Forest Biomass, Timber and a series of other forest products, storehouse of genetic material acting as genetic reservoir for future improvements of Agricultural Production and the most significant, along with the oceans, shelters of the planet’s wildlife. 

Forest ecosystems correspond also to a wide range of humidity values, from dry to very humid regions. Forest ecosystems correspond also to a wide range of humidity values, from dry to very humid regions

  • Tropical Rainforests
  • Temperate Deciduous Forest
  • Temperate Evergreen Forest
  • Tropical Dry Forests
  • Taiga
  • Tundra
  • Grassland Ecosystem

Grassland ecosystems are ecologically and economically important, and are of widespread occurrence. The potential distribution of grassland ecosystems to a large extent is determined by climatic variables, principally temperature and precipitation. Three factors including drought, fire, and grazing by large ungulate herbivores, distinguish grasslands from other ecosystem types. 

They are located in areas in which water availability is below the requirement for the forest at some time during the year but is sufficient to support grasses as the dominant plant type. Grasslands in the wider sense are among the largest ecosystems in the world; their area is estimated to be 40.5 percent of the terrestrial area excluding Greenland and Antarctica

  • Tropical Grasslands (also called savannas)
  • Temperate Grasslands(also known as prairies or steppes)
  • Mediterranean Shrublands (also called chaparral)


Deserts cover 17% of the world’s land mass and harbor almost one-third of terrestrial global carbon stock. A desert often is defined as an area that receives less than 10 inches (25.4 cm) of unevenly distributed precipitation over the year. Much of this land lies between 15° and 30° latitude. The most important factors that affect life in the desert biomes include radiation, heat and temperature, wind, water and nutrition

Despite their aridity, desert ecosystems support a surprising diversity of animal life, including a wide assortment of beetles, ants, locusts, lizards, snakes, birds, and mammals

Key characteristics of the biota are their adaptations to aridity, climate variability, scant summer and winter rainfall patterns and, most importantly, unpredictable rainfall. The adaptations fostering tolerance may take the form of morphological, physiological or behavioural. Some desert plants use deep roots to tap into groundwater. 

Others such as prickly pear and saguaro cacti use widely spread shallow roots to collect water after brief showers and store it in their spongy tissue. Evergreen plants conserve water by having wax coated leaves that minimize evapotranspiration. Others, such as annual wildflowers and grasses, store much of their biomass in seeds that remain inactive, sometimes for years, until they receive enough water to germinate.

Aquatic Ecosystems

An important determiner of the nature of aquatic ecosystems is the amount of salt dissolved in the water. Those that have little dissolved salt are called freshwater ecosystems, and those that have a high salt content are called marine ecosystems. Several other important factors include the ability of the sun’s rays to penetrate the water, the depth of the water, the nature of the bottom substrate, and the water temperature.

Marine Ecosystems:

In oceans the surface area lighted by the sun is small compared to the total volume of water. This small volume of sunlit water and the dilute solution of nutrients limit primary production. All of the seas are interconnected by currents, influenced by wave actions and tides, and characterized by salinity. Vertical stratification is a key feature of aquatic ecosystems. Light decreases rapidly with depth, and communities below the photic zone (light zone, often reaching about 20 m deep) must rely on energy sources other than photosynthesis to persist. 

Temperature also decreases with depth. Warm, bright, near-surface communities, such as coral reefs and estuaries, are among the world’s most biologically productive environments. Temperature also affects the amount of oxygen and other elements that can be absorbed in water. There are broadly two ways in which organisms live in the sea; they float or swim in the water, or they dwell on or within the sea bottom. Hence there are two major divisions of the environment, the Pelagic and the Benthic, the Pelagic Division comprising the whole body of water forming the seas and oceans, and the Benthic Division the entire sea bottom.


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