Energy flow in the ecosystem is unidirectional. Energy obtained is used for various body activities and to overcome entropy. Dissipation of energy occurs as heat.
Ecological Pyramids
An ecological pyramid is a graphic representation of an ecological parameter, like number of individuals present in various trophic levels of food chain with producers forming the base and top carnivores the tip. Ecological pyramids were developed by Charles Elton and are also called eltonian pyramids. An ecological pyramid (1927) can be upright, inverted or spindle shaped.
1. Pyramid of Numbers.
A graphic representation of number of individuals per unit area of various trophic levels the pyramid is upright for grassland and pond but is inverted in parasitic ecosystem.
2. Pyramid of Biomass.
Amount of living or organic matter present in an organism is called biomass. It is a graphical representation of biomass per unit area.
Pyramid of Biomass is upright for terrestrial habitats. Inverted or spindle shaped in aquatic habitats.
3. Pyramid of Energy.
It is graphic representation of amount of energy trapped per unit time and area in
Different trophic levels of a food chain.
Energy content is expressed as kJ/m2/yr. The pyramid is always upright. (See Fig. 4.3-9)
Habitat. A specific place occupied by an organism, population or community which has a particular combination of abiotic factors.
Organisms usually live in specific habitats e.g. annelid Tubifex lives in running and well aerated water having abundant organic matter, Chironomous larvae can survive in water devoid of oxygen. Some fishes can live only in fresh water while some like Hilsa can live in both habitats.
Micro habitat. Part of a habitat which has a specific property of its own due to change in few environmental factors e.g. forest floor, tree canopy, surface of a pond, centre of a pond etc.
Niche. Grinell(1917).
It is a specific part of the habitat occupied by a species circumscribed by its operational requirements and tolerance limits. A population of each species within a community has a separate ecological niche.
The above postulate is supported by Gauses principle of competitive exclusion according to which if two species occupy the same ecological niche only one survives while the organisms occupying similar ecological niche but living in different regions e.g. owl and cat both feed on mice and shrew but while owl in found in deserted area, cats occur around human habitantions.
