Note on Ecological Efficiency, Concept of Productivity and Bio-geo chemical cycle

  • Note
  • Things to remember

Ecological efficiency

Ecological efficiency describes the efficiency with which energy is transferred from one trophic level to the next. It is determined by a combination of efficiencies relating to organismic resource acquisition and assimilation in an ecosystem.

Ecosystem Energetic, Y-shaped energy flow in the ecosystem.

The energy used for all plant life is derived from solar radiation i.e. about 1-10 million of the total solar radiations reaches the earth’s atmosphere. Solar radiation travels through space in the form of waves, wavelength ranges from 300mµ-10mµand above 1cm (radio waves) enter the earth outer atmosphere (which is about 1.8 miles or 28 km altitude.). The energy reaches the earth surface consists largely of visible light and infrared components. On a clear day, the radiation reaching the earth surface is about 10 percent UV, forty-five percent visible and forty-five percent infrared radiation.

About 34 percent of sunlight reaching the earth’s atmosphere is reflected back (by clouds and dust) into its atmosphere, ten percent is held by the ozone layer, water vapor and other atmospheric gases. The rest fifty-six percent reaches the earth surface. Only a fraction of this energy reaching the earth surface is used by green plants by photosynthesis and the rest is absorbed as heat by ground vegetation or water. In fact, only about 0.02 percent of the sunlight reaching the atmosphere is used in photosynthesis. It is a small fraction on which all the organism of the ecosystem depends.

The energy component of energy environment thermal radiation comes from any surface or object i.e. at a temperature above absolute zero. This includes not only soil, water and vegetation but also clouds, which contribute a substantial amount of heat of energy radiated downward into an ecosystem. In this way, in ecosystem energetics, we study about the

  1. A quantity of solar energy reaching an ecosystem.
  2. A quantity of solar energy used by green plants for photosynthesis. And
  3. A quantity of path of energy flows from producer to consumers.
Y-shaped energy flow model
Y-shaped energy flow, model

fig- Graphical representation of Y-shaped model
fig- Graphical representation of a Y-shaped model

In Y-shaped energy flow model, two types of the food chain are showed in a separate arc, one arm represent the grazing and the other arm shows detritus food chain.

The Y-shaped model indicates that food chains are in fact under a natural condition not completely isolated from one another. For instant dead bodies of small animals that were once parts of grazing food chain becomes incorporated in detritions food chain as do the faces of grazing consumption of living plants and ultimate utilization of dead organic matter.

In practice, under natural conditions, the organisms are interrelated in a way that food chains depends on a length of the food chain. Thus, in nature, they operate multi-channel energy flow.

Concept of Productivity:

The productivity of an ecosystem or community is defined as the state at which radiant energy is stored by photosynthetic organisms in the form of organic substances.

Productivity is the accumulation of biomass (organic matter). The production rates differ ecosystem to ecosystem. For examples: higher productivity in tropical rain forest and lowest in arctic and desert ecosystem. High rates of productions, both in natural and cultured ecosystems occur when physical factors are favorable and especially from outside the system that reduces the subsidies from the outside system that reduces the cost of maintenance. Such energy subsidies may take the form of wind and rain of a forest, tidal energy in an estuary or the fossils fuel, animal or human work energy used in the cultivation of crops. There are two types of Productivity.

Primary Productivity

Primary productivity of an ecosystem, community or any part of there is defined as the rate at which radiant energy is stored by photosynthetic or chemo synthetics activity of producers organisms in the form of organic substances which can be used as food materials.

Secondary Productivity:

Secondary productivity is the rate of storage at a consumer level. Since consumer only utilizes food materials already produced, with some respiratory loss and is converted to different tissues by an overall process, gross or net division is not appropriate. Energy flow from producer to herbivores to omnivores and onward is termed as assimilation rather than production. At metabolic equilibrium, photosynthesis equals respiration and this is termed as compensation point.

Methods to study primary productivity in aquatic ecosystem:

  • Oxygen measurement method.
  • Chlorophyll method.
  • CO2 measurement method (Enclosure method)
  • pH method: In aquatic ecosystems, the pH of water is a function of the dissolved CO2 content, which is decrease by photosynthesis and increased by respiration. To use pH as an index to productivity investigator must prepare a calibration curve for the study of water of particular system because pH and CO2 content are no linearly related. The degree of pH change per unit of CO2 changes depends on the buffering capacity of water. The pH meter has been especially useful for the study of laboratory micro system. With pH electrode and recorder continuous photosynthetic of day and respiration of night time from which gross production can be estimated without disturbing the community.

Bio-geo Chemical Cycle:

Hydrological Cycle:

The hydrological cycle begins with the evaporation of water from the surface of the ocean. As moist air is lifted, it cools and water vapor condenses to form clouds. Moisture is transported around the globe until it returns to the surface as precipitation. Once the water reaches the ground, one of two processes may occur; 1) some of the water may evaporate back into the atmosphere or 2) the water may penetrate the surface and become ground water. Ground water either seeps its way to into the oceans and streams or is released back into the atmosphere through transpiration. The balance of water that remains on earth’s surface is a runoff, which empties into lakes, rivers, and streams and is carried back to the oceans, where the cycle begins again.

fig- hydrologic cucle
fig- hydrologic cycle

Lake effect snowfall is a good example of the hydrologic cycle at work. Below is a vertical cross-section summarizing the process of the hydrologic cycle that contribute to the production of lake effect snow. The cycle begins as cold winds (horizontal blue arrows) blow across a large lake, a phenomenon that occurs frequently in the late fall and winter months around the Great Lakes.


E.p., Odum. Fundamentals of Ecology. USA: W.B Saunters Company, n.d.

Jr., Miller G.T. Living in the Environment. Belmont, California, USA: Wadsworth Publishing Company, 2003.

Ecological efficiency describes the efficiency with which energy is transferred from one trophic level to the next. It is determined by a combination of efficiencies relating to organismic resource acquisition and assimilation in an ecosystem.

In Y-shaped energy flow model, 2 types of food chain are showed in separate arc, one arm represent the grazing and the other arm shows detritius food chain


Very Short Questions



No discussion on this note yet. Be first to comment on this note