Pyramid of numbers is the graphic representation of number of individuals per unit area of various trophic levels stepwise, with producers forming the base and top carnivores the tip.

Although best known for the famous statement, ontogeny recapitulates phylogeny, he also coined many words, commonly used by biologists today, such as, phylum, phylogeny and ecology.

Ecological pyramids are also called 'Eltonian pyramids' after C. Elton. Charles Elton (1927) developed the concept of ecological pyramids who noted that , the animals at the base of a food chain, are relatively abundant while those at the end, are relatively few in number.

Eugene Pleasants Odum was an American scientist known for his pioneering work on ecosystem ecology. He wrote the first ecology textbook, 'Fundamentals of Ecology'.

The pyramid of energy represents the total amount of energy consumed by each trophic level. An energy pyramid is always upright as the total amount of energy available for utilisation in the layers above is less than the energy available in the lower levels. This happens because during energy transfer from lower to higher levels, some energy is always lost.

Generally phosphates, are also added to the soil by man, in the form of artificial fertilizers.

In early August, Eugene Odum passed away, at the age of 88, and the world lost one of the most influential figures, in the field of ecology. Dr. Odum has been dubbed “the father of modern ecology” and is credited with pioneering the concept of the ecosystem. His textbook, 'Fundamentals of Ecology' published in 1953, was the catalyst that changed ecology, from the study of the microcosm to the study of the macrocosm.

All of the above are biogeochemical cycles.

Some amount of phosphour, is returned to the earth, in the form of bird's excreta.

Oxides of sulphur, reaches the atmosphere, due to the burning of fossil fuels and volcanic emissions.

It is not phosphorus, but water which is important for the working of macromolecules.

The major process, that brings carbon form the atmosphere, into the living world is photosynthesis, where producers take in carbon dioxide from the atmosphere, and convert it into organic compounds. Oxygen is released as a by product. Carbon fixed by the producers, enters the food chain, and is passed to herbivores, carnivores and decomposers

Some amount of phosphorus is returned to the earth, in the form of bird's excreta - Guano deposits (excreta of marine birds) and dead fish (around 60,000 tonnes which is less than 0.5% of phosphorus discharged from rivers)

In sedimentary cycles, the elements main reservoir pool, is lithosphere and the biogenetic materials involved in circulation, are non-gaseous. The sedimentary cycles are usually very slow, as the elements may get locked up in rocks, and go out of circulation, for long periods.Though sulphur occurs in gaseous form, as hydrogen sulphide (H₂S) and sulphur dioxide (SO₂), the residence time of sulphur in atmosphere is very small (about 4 x 10¹⁰ kg) and its main reservoir pool is the soil (contains about 4 x 10¹⁸ kg in the form of sulphates, sulphides and organic sulphur). So, sulphur cycle, is classified under sedimentary cycles.

The greatest reservoirs of phosphate are the insoluble ferric and calcium phosphates in rocks (rock phosphate), in combination with calcium, iron and aluminium. Slow process of weathering releases phosphates into the soil.

Pyramid of biomass, is the graphic representation of producers at the base and top carnivores at the tip.

Heterotrophic bacteria, like Desulfavibrio and Acetobacter reduce sulphates to elemental sulphur or sulphides, under anaerobic conditions. Though sulphides are harmful to most organisms, sulphur bacteria oxidise them to sulphate, and brings back the element to cycle.

An ecosystem can be defined as a structural and functional unit of biosphere or segment of nature consisting of community of living beings and the physical environment, both interacting and exchanging materials between them.

The series of populations or organisms, of an ecosystem, through which food and energy contained in it passes with each member becoming the food of the later, is called a food chain.

The pyramid of energy, represents the total amount of energy consumed by each trophic level. An energy pyramid is always upright, as the total amount of energy available for utilization in the layers above, is less than the energy available in the lower levels. This happens because during energy transfer from lower to higher levels, some energy is always lost.

Biome, is a large, regional or sub continental biosystem characterized by a major vegetation type or other distinct landscape characters, such as, tropical deciduous forest, tundra biome, etc. The major terrestrial ecosystems (largest ecological units) of distinctive terrestrial areas, with their climax plants and associated animals, are known as Biomes.

In nature, food chain relationships are not isolated. They are very complex, as one organism may form the food source of many organisms. Thus, instead of a simple linear food chain, there is a web like structure formed by these interlinked food chains. Such interconnected matrix of food chains, is called 'food web'

Biotic Components, are all the living beings, in an environment, from protists to mammalians. Individuals should have specific behavioral and physiological characteristics, that permit their survival and reproduction, in a defined environment. The condition of sharing an environment, generates a competence among the species, competence that is given for food, space, etc.

A well known case of symbiosis, corresponds to lichens. Lichens organize from an obliged interaction, between a fungus and a green alga. The interaction is extreme, because the individuals not only do not belong to the same species, but they do neither belong to the same kingdom. The fungus provides an adequate humid bed to the algae, and this provides with free food, to the fungus. The relation has occurred so narrowly in the course of the evolution, that an isolated species, cannot subsist without the other.

Energy and nutrients, pass through various alimentary levels. Each one of those levels, is called trophic levels in Ecology. The sum of all the trophic levels of an ecosystem, is called food chain. The alimentary relationships in an ecosystem, are called food web.