Food Web or Food Cycle: Different food chain is often interconnected with one another. For example, specific herbivores of one food chain may serve as good of carnivores of several other food chains. This interlocking pattern of several food chains is also called as food web.
The following types of food chains are interconnected to form a food web:
Grass —–grass hoper—–hawk
Grass ——-grass hopper——lizard———hawk
Characteristics of food Webs:
i) No food chain is independent in an ecosystem.
ii) Food web is formed by the interlinking of three types of food chain i.e. predatory food chain, parasitic chains and saprophytic food chain.
Significance of Food Web:
i) The food webs provide the alternative pathways of food availability e.g. If a particular crop is destroyed due to some disease, the herbivorous in that area do not perish as these can graze can on other types of crops or vegetation.
ii) Stability of an ecosystem depends on the number of pathways available.
iii) It helps in checking overpopulation of the species.
iv) They also help in ecosystem development.
Energy flows in Ecosystem
Energy is the simple most essential requirement of all living things. The storage and expenditure of energy in the ecosystem are based on two basic of thermodynamics. According to first law, energy is neither created or destroyed, but can be transferred from one component to another and 2nd law states that no energy transformation occurs spontaneously unless some energy is degraded or dissipated.
In ecosystem, the energy of sunlight can be transformed into food and heat. The transfer of food energy from one organism to another leads to degradation and loss of major fraction of food energy as heat due to metabolic activities, with only small fraction being stored in living tissues or biomass. While energy in food is in concentrated form, heat energy is highly dispersed. Under favorable environment conditions, only about 1-5% of energy of incident radiation, or 2-10% of photosynthetic process (Grass Primary Productivity) and the remaining portion in dissipated. Since the simultaneously occurring preparatory process are energy consuming and sue part of photosynthetic gain, the capture of energy (net primary productivity)is reduced to only 0.8-4% of the incident total radiation or 1.6%-8% of PAR. Only the energy captured in the net productivity of producers can be used by other trophic levels.
Thus, regarding the energy flow an ecosystem is characterized by:
i) Unidirectional flow of energy
ii) Decrease in free energy
iii) Return of radiant energy of sun to non-living system as heat.
Nutrient Cycling in an Ecosystem: Plants absorb varying amounts of nutrients from the soil. Due to decomposition of dead organic matter, nutrients are continuously regenerated and stored in soil in the soil in the forms available to the plant. Nutrients, which are necessary for growth of living organisms, continually exchanged between organism and physical environment in more or less circular manner. This is called as nutrient cycle or bio-geo-chemical cycle.
The nutrient cycle is of two types, the gaseous and the sedimentary. The reservoir of gaseous type of nutrient cycle (nitrogen, carbon, oxygen etc) is generally located in the atmosphere where as reservoir of sedimentary type (phosphorus, Sulphur etc.) is located in Earth’s crust.
Detail and Significance of Food Web and Nutrient Cycling in an Ecosystem