Self regulating ecosystems without much interference and manipulations are natural system e.g. Pond, forest, grassland, desert.
The city and cropland ecosystems are manmade ecosystems so are called artificial ecosystems. Ecosystem which do not contain all the four basic components of ecosystems (i.e. abiotic, biotic and decomposers) and they lack one or more basic components are incomplete ecosystems.
The sun light is trapped by plants in a year, and plant material is eaten by herbivores and herbivores are eaten by carnivores. The functions of “ecosystems are:
(a) Flow of energy
(b) Cycle use of materials
Food chains and Food webs
Organisms of an ecosystem are linked together in food chains. Organic nutrients are transferred from producer to consumers and decomposers as organisms eat and in turn are eaten by other organisms. The food chain is divided into tropic levels comprised of all the organisms that obtain their food by an identical numbers of steps. In a given population may have are or more than one tropic levels according to source of energy assimilated. At each transfer of energy from one tropic level to another, a larger part is degraded as heat. If the food chain is shorter, the greater food energy is available.
The producers or the autotrophs (green plants) comprise the first tropic level. The herbivores, which consume the plants, comprise the second tropic level. Carnivores that consume the herbivores are third tropic level. Carnivores which consume third level carnivores comprise the fourth tropic level. All food chains begin at the producer level and all end at the decomposer level.
The sequence of eating and being eaten, with the resultant transfer of energy is known as food chain. Each step is known as tropic level and study of energy flow through these steps are called tropic ecology. The food chains are not isolated from one another and food chains are interlocked with one another and this inter-connecting network of species is known as food web.