The maintenance of the integrity of the community is ensured by a variety of connections between organisms. Food connections are of the greatest importance in nature, due to which there is a continuous material-energy exchange between the living and inanimate matter of nature.
In a community, living organisms are closely related not only to each other, but also to inanimate nature. This connection is expressed through the flow of food, water, oxygen into living organisms from the environment. Food contains energy that is necessary for the body to function. Thus, the biocenosis can stably exist only with the redistribution of matter and energy through food chains.
For any community, you can draw a diagram of all the nutritional relationships of organisms. This scheme looks like a network (its interlacing is very complex) and is called the food (trophic) web.
Example: food web of deciduous forest:
The food web is formed by several food chains, in each of which there is a transfer of matter and energy.
In each chain, there is a unidirectional flow of matter and energy from one group of organisms to another (in the figure, the arrows show the transfer of matter).
Food chains that begin with living organic matter (usually green plants) are called grazing or consumer chains (or grazing chains).
Grassland food chains are dominant in herbaceous, aquatic ecosystems.
Example: A – grazing food chain: live plant – herbivorous insect – insect of prey – insectivorous bird – bird of prey.
Trophic chains that begin with dead organic matter of detritus (dead plant remains, corpses and animal excrement) are called detrital, or reductive, chains (or decomposition chains).
Detrital chains are predominant in forest ecosystems.
Example: B – detrital food chain: fallen leaves (detritus) – soil bacteria, worms, fungi (detritivores) – soil insects and mites – predatory insects and insectivores.