Our Environment

• In a food chain, along with food, transfer of energy also occurs from one trophic level to the other. The flow of energy which occurs along a food chain is called energy flow.
• All living organisms in an ecosystem require energy for carrying out various life processes such as breathing, growth and movement. This energy supports various activities of the living world.
• All the energy used by living organisms is obtained from the Sun. Solar energy enters the living components through the autotrophs or green plants, where it gets converted into chemical energy. However, only 1% of the total energy is actually captured by green plants. 
• The food energy produced by plants is partially used by them for their growth and development. A major part of it is lost as heat energy.
• The plants are then eaten by primary consumers, the herbivores, and the energy stored in plants is transferred to these organisms. A part of the energy is used by herbivores for activities such as digestion, growth and reproduction. Again, most of the energy is lost to the environment in the form of heat.
• When herbivores are consumed by carnivores, a part of the energy is used by the carnivores for their metabolic activities and growth, while most of it is released as heat energy.
• The amount of energy gradually declines as one move up to each higher trophic level, because at each level, energy is lost in the form of heat.
  
  
  
  
• Due to the loss of energy at each step, food chains consist of only three to four trophic levels. If there are many levels, then animals at the end of the food chain will not have enough food and energy to survive. The solar energy converted by the autotrophs into food energy cannot be reconverted into solar energy, and the energy which passes from the herbivores to the carnivores can never go back to the herbivores. The energy lost as heat cannot be returned to the plants and reused during photosynthesis. Therefore, the flow of energy through a food chain is always unidirectional. 

Food Web                                                          

• Similar kinds of organisms may occur in more than one food chain. They eat more than one type of food to satisfy their requirements. A plant of a particular species can serve as food for a variety of herbivores. 
• No food chain can operate in isolation. Individual food chains are interconnected in a complex way. 
• A network of interconnecting food chains in a natural community of different organisms is called a food web.

Example of Food Web

• Consider six food chains which are interconnected to form a food web. The food web begins with plants and ends with the top carnivore, the vulture.
• In the first food chain, the plants are eaten by the grasshopper, and the grasshopper, in turn, is eaten by the vulture.
  Plants → Grasshopper → Vulture
• In the second food chain, the plants are eaten by the rabbit. The rabbit is then consumed by the vulture.
  Plants → Rabbit → Vulture
• In the third food chain, the plants are eaten by the rat. The rat is then eaten by the vulture.
  Plants → Rat → Vulture
• In the fourth food chain, the plants are eaten by the rat, the rat is eaten by the snake, and the snake, in turn, is eaten by the vulture.
  Plants → Rat → Snake → Vulture
• In the fifth food chain, the plants are eaten by the grasshopper, and the grasshopper, in turn, is eaten by the frog. The frog is eaten by the snake, and the snake is consumed by the vulture.
  Plants → Grasshopper → Frog → Snake → Vulture
• Finally, in the sixth food chain, the plants are eaten by small birds which in turn are eaten by the vulture.
  Plants → Small birds → Vulture
  
  

Significance of Food Web

• Food webs permit alternative foods.
• They ensure a better chance of survival of an organism if any of its food sources is scarce.

Ecological Pyramid

• An ecological pyramid is a graphical representation of an ecological parameter, like number or biomass or accumulated energy at different trophic levels in a food chain in an ecosystem.
• These pyramids are also called Eltonian pyramids named upon the discovery by Charles Elton in 1927.
• The base of the pyramid always represents the producers or the first trophic level and the apex represents top level consumer or the last trophic level.
• Ecological pyramids are of three types- 

1. Pyramid of number
2. Pyramid of biomass 
3. Pyramid of energy
   
   
   
   
   
   

Depletion of the Ozone Layer