Community Level Systems: Food Chains and Food Webs

Community Level Systems: Food Chains and Food Webs

Understanding Food Chains

  • A food chain is a linear sequence illustrating the flow of energy and nutrients from one organism to another in an ecosystem.
  • It begins with producers, typically plants or algae, which can make their own food using light energy from the sun, carbon dioxide from the air and water from the soil. This process is known as photosynthesis.
  • Producers are then eaten by primary consumers, which are usually herbivores.
  • These primary consumers are then preyed on by secondary consumers, which are typically carnivores.
  • At higher levels, we have tertiary consumers and quaternary consumers, which are the top predators in the food chain and usually have no predators of their own.
  • The final link in all food chains is the decomposer, such as bacteria and fungi, which break down dead material and waste products into simple materials.
  • The materials produced by decomposers are returned to the soil and can be used by plants to carry out photosynthesis, thereby starting the cycle again.

Food Webs and Interconnected Chains

  • A food web is a more realistic representation of feeding relationships, as it includes multiple interconnected food chains.
  • Most organisms eat, and are eaten by, more than one species. A food web recognises this complexity.
  • A change in the population of one species has a knock-on effect on the other species in the food web.
  • This can lead to increases or decreases in populations of organisms at different levels of the food web.

Energy Flow and Trophic Levels

  • The position of an organism in a food chain or food web is referred to as its trophic level.
  • Energy is lost at each trophic level, primarily through waste products and heat during respiration. As a result, there is less energy available for the next level. This is why there are usually only four or five trophic levels.
  • Conservation of energy dictates that only around 10% of the energy at one trophic level is transferred to the next level, leading to a pyramid of energy with the highest energy at the bottom (Producer level) and the lowest at the top (highest consumer level).

Biomagnification and Pollution

  • Certain harmful chemicals introduced into the environment, such as heavy metals or pesticides, can accumulate in organisms. This process is known as bioaccumulation.
  • Biomagnification refers to the increase in concentration of these harmful substances at each successive trophic level in a food chain.
  • The top-tier predators, such as eagles and humans, are most affected by biomagnification, which can lead to serious health problems.