Food Chain and Food Web

Introduction

• Food chain is a feeding hierarchy in which organisms in an ecosystem are grouped into trophic (nutritional) levels and are shown in a succession to represent the flow of food energy and the feeding relationships between them
• A food web is the natural interconnection of food chains and a graphical representation of what-eats-what in an ecological community
• Food chains intertwine locally into a food web because most organisms consume more than one type of animal or plant
• Major parts of Food Chain
  • Sun: This is the initial source of energy, which provides energy for everything on the planet
  • Producers: This is the first stage of Food Chain. These are any plant or other organisms that produce their own nutrients through photosynthesis
  • Consumers: These are all organisms that are dependent on plants or other organisms for food. This is the largest part of a food web, as it contains almost all living organisms
  • Decomposers: These are organisms that get energy from dead or waste organic material. This is the last stage in a food chain, and they convert organic waste materials into inorganic materials like nutrient-rich soil or land
• Because energy, in the form of heat, is lost at each step, or trophic level, chains do not normally encompass more than four or five trophic levels

Types of Food Chains

• Two types of food chains are present in ecosystems:

1. Grazing food chain
   • Grazing animals play an important role in the transfer of energy to the carnivores in this type of food chain, hence the name grazing food chain.
   • Green plants in the terrestrial ecosystems and phytoplankton in the aquatic ecosystems are the producers.
   • The primary consumers are the cattle, sheep, rabbits, deer, insects, and snails which feed on the green plants in the terrestrial ecosystems and the zooplankton, fishes and animals which feed on phytoplankton in the aquatic ecosystems.
   • In the soil the unconsumed dead organisms and biological wastes become the food for the detritivores of the detritus food chain.
   • Herbivores (the primary consumers) are eaten by the secondary consumers or primary carnivores.
     • Similarly secondary consumers are eaten by the tertiary consumers or secondary carnivores.
   • The grazing food chains are linear and are usually with 4 to 5 trophic levels in the chain
   • Examples
     • In terrestrial Ecosystem
       • Grass
       • Grass
     • In aquatic Ecosystem
       • Phytoplankton

2. Detritus Food Chain
   • It starts from dead organic matter of decaying animals and plant bodies consumed by the micro-organisms and then to detritus feeding organism called Detrivores or Decomposers and to other predators
   • Examples
     • Litter → Earthworms→ Chicken → Hawak

• The distinction between these two food chains is the source of energy for the first level consumers
  • In the grazing food chain, the primary source of energy is living plant Biomass; while in the detritus food chain the source of energy is dead organic matter or detritus
• The two food chains are linked as well
  • The initial energy source for detritus food chain is the waste materials and dead organic matter from the grazing food chain

Food Web

• A food web is a graphical model depicting the many food chains linked together to show the feeding relationships of organisms in an ecosystem
• It differs from a food chain in a way that the latter is a linear system showing a succession of organisms whereby each species is eaten in turn by another species
  • While Food web is a more complex network of what-eats-what in a particular ecosystem
• The diagram below shows an example of a food web

• In food webs, arrows point from an organism that is eaten to the organism that eats it. As the food web above shows, some species can eat organisms from more than one trophic level

Concept Check!

Differences: Food Chain vs Food Web

• Energy is transferred between trophic levels when one organism eats another and gets the energy-rich molecules from its prey’s body. However, these transfers are inefficient, and this inefficiency limits the length of food chains
• When energy enters a trophic level, some of it is stored as biomass, as part of organisms’ bodies.
  • This is the energy that’s available to the next trophic level since only energy storied as biomass can get eaten.
  • As a rule of thumb, only about 10% of the energy that’s stored as biomass in one trophic level—per unit time—ends up stored as biomass in the next trophic level—per the same unit time
  • This pattern of fractional transfer limits the length of food chains; after a certain number of trophic levels—generally three to six, there is too little energy flow to support a population at a higher level