Study Notes on Ecosystem

  • An ecosystem can be visualised as a functional unit of nature, where living organisms interact among themselves and also with the surrounding physical environment.
  • Ecosystem varies greatly in size from a small pond to large forest or a sea.
  • Many ecologists regard the entire biosphere as a global ecosystem, as a composite of all local ecosystems on Earth.
  • Since this system is too much big and complex to be studied at one time, it is convenient to divide it into two basic categories, namely the terrestrial and the aquatic.
  • Forest, grassland and desert are some examples of terrestrial ecosystems; pond, lake, wetland, river and estuary are some examples of aquatic ecosystem.


  • Interaction of biotic and abiotic components result in a physical structure that is characteristic for each type of ecosystem.
  • Identification and enumeration of plant and animal species of an ecosystem gives its species composition.
  • The Vertical distribution of different “decies occupying different levels is called stratification. For example, trees occupy top vertical strata or layer of a forest, shrubs the second and herbs and grasses occupy the bottom layers.
  • The components of the ecosystem are seen to function as a unit when you consider the following aspects:

(i) Productivity;

(ii) Decomposition;

(iii) Energy flow; and

(iv) Nutrient cycling.


  • A constant input of solar energy is the basic requirement for any ecosystem to function and sustain.
  • Primary production is defined as the amount of biomass or organic matter produced per unit area over a these period by plants during photosynthesis.
  • It is expressed in terms of weight ( 7 cl energy (kcal m2). The rate of biomass production is called productivity
  • It is expressed in terms of gayr” or (kcal m) yr to compare the productivity of different ecosystems.
  • It can be divided into gross primary productivity (GPP) and net primary productivity (NPP). Gross primary
  • productivity of an ecosystem is the rate of production of organic matter during photosynthesis.
  • A considerable amount of GPP is utilised by plants In respiration.
  • the Gross primary productivity minus respiration losses (R). is the net primary productivity (NPP). GPP-R = NPP.


  • You may have heard of the earthworm being referred to as the farmer’s ‘friend’.
  • This is so because they help in the breakdown of complex organic matter as well as in loosening of the soil.
  • Similarly, decomposers break down complex organic matter into inorganic substances like carbon dioxide, water and nutrients and the process is called decomposition.
  • The Dead plant remains such as leaves, bark, flowers and dead remains of animals, including fecal matter, constitute detritus, which is the raw material for decomposition.
  • The important steps in the process of decomposition are fragmentation, leaching, catabolism, humification and mineralisation.


  • Except for the deep sea hydro-thermal ecosystem, sun is the only source of energy for all ecosystems on Earth.
  • the incident solar radiation less than 50 per cent of it is photosynthetically active radiation (PAR).
  • We know that plants and photosynthetic and chemosynthetic bacteria (autotrophs), fix suns’ radiant energy to make food from simple inorganic materials.
  • The Plants capture only 2-10 per cent of the PAR and this small amount of energy sustains the entire living world.
  • It is very important to know how the solar energy captured by plants flows through different organisms of an ecosystem.
  • All organisms are dependent for their food on producers, either directly or indirectly. So you find unidirectional flow of energy from the sun to producers and then to consumers.
  • Detritivores are e.g., earthworm) breal dom ‘eritus into smaller particles.
  • All animals depend on plants (directly or indirectly) for their food needs.
  • They are hence called consumers and also heterotrophs. If they feed on the producers, the plants.
  • they are called primary consumers, and if the animals eat other animals which in turn eat the plants (or their produce) they are called secondary consumers.
  • Likewise, you could have tertiary consumers too, Obviously the primary consumers will be herbivores.
  • Some common herbivores are insects, birds and mammals in terrestrial ecosystem and molluscs in aquatic ecosystem.
  • The consumers that feed on these het verse are carnivores, or more correctly primary carnivores (though secondary consumers).
  • Those animals that depend on the primary carnivores for food are labelled secondary carnivores.


  • The base of a pyramid is broad and it narrows down at the apex. One gets a similar shape, whether you express the food or energy relationship between organisms at different trophic level.
  • Thus, relationship is expressed in terms of member biomass or energy.
  • The base of each pyramid represents the producers or the first trophic level while the apex represents tertiary or top level consumer.
  • The three ecological pyramids that are usually studied are a pyramid of number; (b) pyramid of biomass and (c) pyramid of energy.


  • the characteristics of population and community and also their response to environment and how such responses vary from an individual response. Let us examine another aspect of community response to environment over time.
  • An important characteristic of all communities is that their composition and structure constantly change in response to the changing environmental conditions.
  • This change is orderly and sequential, parallel with the changes in the physical environment.
  • These changes lead finally to a community that is in near equilibrium with the environment and that is called a climax community.
  • The gradual and fairly predictable change in the species composition of a given area is called ecological succession.


  • Based on the nature of the habitat – whether it is water (or very we areas) or it is on very dry areas – succession of plants is called hydrarch or xerarch, respectively.
  • Hydrarch succession takes place in wetter areas and the successional series progress from hydric to the mesic conditions.
  • As against this, xerarch succession takes place in dry areas and the series progress from xeric to mesic conditions. Hence, both hydrarch and xerarch successions lead to medium water conditions (mesic) – neither too dry (xeric) nor too wet (hydric).


  • Healthy ecosystems are the base for a wide range of economic, environmental and aesthetic goods and services.
  • The products of ecosystem processes are named as ecosystem services, for example, healthy forest ecosystems purify air and water, mitigate droughts and floods, cycle nutrients, generate fertile soils, provide wildlife habitat, maintain biodiversity, pollinate crops, provide storage site for carbon and also provide aesthetic, cultural and spiritual values.
  • Though value of such services of biodiversity is difficult to determine, it seems reasonable to think that biodiversity should carry a hefty price tag.