Ecosystem or biocenosis is a segment of nature/ biosphere consisting of a community of living beings and the abiotic/physical environment both interacting and exchanging materials between them. Ecosystem can be temporary (e.g. rain water pond) or permanent, natural or man-made (e.g. aquarium, agriculture), small or large.
They include all living beings present in an ecosystem producers, consumers and decomposers. The components are connected through food, its contained energy and a web of interrelationships.
They arc autotrophs that manufacture organic compounds from inorganic raw materials with the help of solar energy. Producers are also called transducers as they convert solar radiations into chemical energy. Besides food, producers give out oxygen and take in carbon dioxide.
They are heterotrophs, mostly animals which feed on other organisms. Consumers are also called phagotrophes as they ingest food. Herbivores/First Order Consumers. They feed on producers. Also called key industry animals (Elton, 1927), e.g. Deer, Rabbit, Cattle, Goat/Sheep, Grasshopper, protozoans, molluscs, many crustaceans. Primary Carnivores/second orders consumers. Feed on primary carnivores, e.g. Owl, Peacock. Top Carnivores. Carnivores which are not preyed upon, e.g Lion.
They are saprotrophs which decompose the organic remains by secreting extracellular digestive enzymes. Due to degradation of organic remains, decomposers are also called reducers. They are also known as mineralisers as they release minerals trapped in organic remains. Detrivores are decomposers, as well as scavengers. Scavangers are consumers of dead bodies, e.g. Vulture, Carrion Beetle. Parasites are consumers that feed on small part of a living being.
(a) Temperature (b) Light (c) Wind/Air current (d) Humidity/Precipitution (e) Water (f) Topography (g) Back ground. Trophic Levels
They are steps or divisions of food chain characterised by specific method of obtaining food. Producers belong to T or first trophic level, herbivores/primary consumers T,, primary carnivores/ secondary consumers Tv secondary carnivores T4 etc. Parasites do not have any fixed trophic level. Decomposers constitute the last or deteritus trophic level. Guild is the group of species belonging to the same trophic level and exploiting the same resource.
(A) Food Chain:
It is the sequence of populations/organisms through which food and its contained energy pass in an ecosystem with members at one step becoming food of later step of the sequence. Common food chains are predator food chains.
Detritus food chain is the shortest. Parasitic food chain is the third type.
(a) Aquatic Food Chain:
Phytoplankton -> Zooplankton -> Small
Crustaceans -> Water Insects -> Small Fish -> Larger
Fish -> King Fishes.
(b) Land Food Chain:
Grass -> Grasshopper -> Frog -» Snake -> Peacock -> Falcon -> Eagle.
Herbs -> Rabbit -> Fox -> Wolf -> Tiger
(B) Food Web:
It is a network of food chains which are interconnected at different trophic levels so as to form a number of feeding connections amongst members of a biotic community, e.g. Rabbits preyed upon by Wild dog, Fox, Wild cat and Jackal. These carnivores can also prey upon mice, shrews, and squarrels. Wolf preys upon Jackal, Fox, Wild cat and Sheep/goat. It is eaten by Tiger. Tiger preys upon Deer, Antelope and a number of other animals. In Sunderbans, Tiger does not have its natural preys. It feeds there on fish and crabs.
Flow of Energy:
Ecosystem is continuously obtaining solar energy which is trapped by producers-1.15% in grasslands, 0.9% in Savannah, 0.81 % in mixed forest, 5% in crops and 10-12% in sugarcane. The rest is dissipated as heat. A part of energy stored in food is released during respiration.
Some of the released energy is used in carrying out body activities while the rest is dissipated. Herbivores feed on producers. Part of the food energy is wasted in digestion and assimilation. Some of the assimilated food is broken down to release energy for performing body activities.
Some of the energy is lost as heat. A very small portion becomes part of the body of herbivore. Herbivores are eaten by primary carnivores, the latter by secondary carnivores and so on. At every step, a lot of energy is wasted. Flow of energy in an ecosystem is unidirectional.