Ecosystems are often classified by reference to the biotopes concerned. The following ecosystems may be defined:
Continental ecosystems (or terrestrial), such as forest ecosystem (temperate forests, boreal forests, or taiga, tropical rainforest), meadow ecosystems (meadows, steppes, savanna, tundra), deserts (hot and dry, semiarid, coastal, cold deserts) or agro-ecosystems (agricultural systems).
Ecosystems of inland waters, such as lentic ecosystems (lakes, ponds) or lotic ecosystems (rivers)
Oceanic ecosystems (seas, oceans).
Another classification can be done by reference to its communities (for example a human ecosystem).
The human ecosystem (urban ecosystem) concept is grounded in the deconstruction of the human/nature dichotomy and the premise that all species are ecologically integrated with each other, as well as with the abiotic constituents of their biotope.
6.Liebig'sLaw of the Minimum
The importance of a single environmental factor was recognized by a German chemist, Justus von Liebig. He first formulated theLaw of the Minimum in 1840 which states that growth is controlled not by the total of resources available, but by the scarcest resource. Only by increasing the amount of the limiting nutrient (the one scarcest in relation to "need") was growth of a plant or crop improved.
Liebig is known as the "father of the fertilizer industry" for his great contributions to the science of plant nutrition and soil fertility. He downplayed the role of humus in plant nutrition and discovered that plants feed on nitrogen compounds and carbon dioxide (CO2) derived from the air, and hydrogen (H) and oxygen (O2) from water as well as minerals in the soil. One of his most recognized accomplishments was the invention of nitrogen-based fertilizer. Which are now widely used throughout the world, and their production is a substantial segment of the chemical industry.
Liebig's Law has been extended to biological populations. For example, the growth of a biological population may not be limited by the total amount of resources present throughout the year, but by the minimum amount of resources available to that population at the time of the year of greatest scarcity. The growth of a population of animals might depend not on how much food was available in summer; rather on how much food was available in winter.
7. V. E. Shelford expanded Liebig’s Law, applying it also to animals and taking into account that too much may be as bad as too little. Shelford’s Law of Tolerancestates that the existence, abundance, and distribution of a species in an ecosystem will be limited by its range of tolerance for local environmental factors. Thus, distribution of a species are determined by whether the levels of one or more physical or chemical factors fall within the range tolerated by that species
In other words, there are minimum and maximum limits for physical conditions (such as temperature) and concentrations of chemical substances-called tolerance limits-beyond which no members of a particular species can survive. This concept of the limiting effect of maximum as well as minimum was incorporated into the ‘law’ of tolerance by V. E. Shelford in 1913.
Though the principle behind both Liebig’s and Shelford’s laws is important in ecology, the assumption that a single factor is always limiting is potentially misleading. In nature, the various environmental factors interact in so many ways that it is often impossible to describe any one factor as the liming one.