Functioning of an Ecosystem

Functioning of an Ecosystem

An ecosystem is driven by the flow of energy and circulation of matter by biogeochemical cycle between the biosphere, lithosphere, hydrosphere and atmosphere. The solar radiation is the basic input of energy entering the ecosystem. In the living organisms or biosphere, the energy (chemical energy) and matter (food), collectively called as food energy, are transferred via food chain and food web through various trophic levels. Thus all the elements of an ecosystem are interdependent and integrated. An ecosystem itself is integrated with other ecosystems and thus they all become interdependent. In fact every ecosystem is part of the larger ecosystem, until the larger ecosystem of the earth-the biosphere – is formed. That is why we see climatic changes happening in one ecosystem affecting the other ecosystems.

Productivity of Ecosystem

Only a small fraction of sunlight striking the earth is concerted to chemical energy by primary producers. The rate of conversion of solar energy into chemical energy (organic matter) by autotrophs is called productivity of ecosystem. The productivity of ecosystem depends to two things:-

(i)                  The availability of solar radiation to autotrophic primary producers. The productivity of ecosystems goes in decreasing from equator to poles as the amount of solar energy received goes on decreasing from equator to poles. Therefore, plants in tropical areas will have higher productivity than plants in temperate or tundra region.

(ii)                The efficiency of plants to concert solar energy into food or chemical energy which is also called as primary production. It is measured in two ways:

(a)    Gross primary productivity which is total amount of chemical energy assimilated by the autotrophs from solar energy.

(b)   Net Primary Productivity is equal to Gross Primary Productivity minus the energy lost through respiration.

The Respiration means energy required to keep the metabolism of an organism going on. So highly mobile organisms as well as higher life forms such as mammals have higher respiratory rate. Complex plants such as those in tropical rainforests have higher respiratory rate than simple plants like algae or grasslands. Net primary productivity represents the usable amount of energy at the first trophic level, which is made available to higher trophic levels.

(iii)               Other than sunlight, the efficiency of the plants is also limited by nutrient availability. Generally the limiting nutrients are nitrogen or phosphorous but most often water and temperature, together limit the productivity of an ecosystem. For example, the Polar Regions having less sunlight and desert regions having less water have lower productivity. Besides these there are biological factors like mutualism, parasitism, predation, etc which increase the productivity of an ecosystem.

Secondary Productivity: The rate at which ecosystem’s consumers convert the chemical energy of the food they eat into their own new biomass in called the secondary productivity.

Energy Efficiency: The concept of primary and secondary productivity a gives the idea of energy efficiency. Not all the energy produced at one trophic level is available for transfer to next trophic level (as stored food energy) but majority is lost in respiration.

Energy efficiencies or trophic efficiency refers to the energy transferred to the next level. Tropic efficiencies generally range from 5 to 20% e. g. plants transfer around 7 – 10% of total energy produced by them to the herbivores. Herbivores being mobile have higher metabolic respiration. As a result relative loss of energy increases at successively higher trophic levels.

A common way of illustrating ecological efficiency is via pyramids of productivityThere are a few other terms. Biomass refers to the quantity or weight of living matter per unit area per unit time. It is represented in terms of dry weight. Biomass is comprised of plants and animals and therefore it is referred to as plant biomass or animal biomass.

Total plant biomass including above ground and subsurface plants is called standing crop.

On the basis, the Productivity of ecosystem refers to the rate of increase of biomass whereas Production is the amount of biomass of a given unit area at a given time. Mean net primary productivity for the whole earth is 320 dry gram/m2/ year. Also the productivity of continental ecosystems is higher than that of marine ecosystems.