Energy flow in the Ecosystem: Trophic levels, Food Web and Ecological Pyramids

Trophic levels

1. Depending on their feeding relationship with other species, organisms occupy a location in the natural setting or a group.
   1. Organisms occupy a particular position in the food chain known as their trophic level based on the source of their nutrition or food. Producers are in the first trophic stage, followed by herbivores (primary consumers) and carnivores (secondary consumers).
   2. Autotrophs: They are the food producers for the ecosystem’s other species. They are mostly green plants that use photosynthesis to turn inorganic material into chemical energy in the presence of solar energy (food). Gross Primary Production (GPP) refers to the overall amount at which radiant energy is accumulated in green plants through the photosynthesis process. This is known as total assimilation or total photosynthesis. From the GPP, a part is utilized by the plants for its metabolism. The remainder is retained as Net Primary Production (NPP) by the plant and made accessible to consumers.
   3. Herbivores: The animals which eat the plants directly are called herbivores or primary consumers. Ex: birds, ruminants, insects, and rodents.
   4. Carnivores: They are secondary consumers and they feed on herbivores, and tertiary consumers if they use carnivores as their food. Ex: frog, tiger.
   5. Omnivores: Animals that eat both plants and animals. Ex: bear, pig.
   6. Decomposers: They take care of the dead remains of organisms at each trophic level and help in recycling the nutrients. For example Fungi and bacteria.                                                                                                                                                             When an organism dies, it is reduced to detritus, or dead biomass, which decomposers use as an energy source. The energy demands of organisms at each trophic level are met by those at the lower trophic level. The energy is decreased at successive trophic levels.  At any given time, each trophic level has a certain mass of living material known as the standing crop. The mass of living organisms (biomass) or the amount in a unit area is used to calculate the standing crop. A species’ biomass is measured in either fresh or dry weight.

Food web

1. Trophic levels do not follow a linear pattern in an ecosystem. They are linked together to form a food web. So, the food web is a matrix of interconnected food chains.
2. The Food web is a more realistic and practical model of energy flow through an ecosystem. In nature, one often finds food webs rather than food chains.
3. It is possible that one animal is a member of several food chains.
4. If any one of the intermediate food chains is removed, the succeeding links of the chain will automatically suffer. Most species in an ecosystem have more than one food source thanks to the food web, which increases their chances of survival.
5. For example, grasses may serve food for rabbits or grasshoppers or goats, or cows. Similarly, a herbivore may be a food source for many carnivorous species.

Ecological pyramids

In an ecosystem, the graphic representations of trophic levels are called ecological pyramids. They have a pyramidal shape to them. The pyramid’s base is made up of producers, with the subsequent tiers representing herbivore, carnivore, and top carnivore levels. The ecological pyramids can be categorized into three types. Pyramid of numbers: This represents the number of organisms at each trophic level. It graphically represents the total number of individuals of different species, belonging to each trophic level in an ecosystem.

1. 1. 1. For example, in a grassland system, the number of grasses outnumbers the number of herbivores that eat them, and the number of herbivores outnumbers the carnivores number. In a few cases, the pyramid of numbers may be inverted, i.e., herbivores are more than primary producers. For example, when many caterpillars and insects feed on a single tree.
      2. Upright Pyramid of Numbers: The number of individuals decreases as you progress from the lowest to the highest trophic level in this pyramid. In the grassland biome, this sort of pyramid can be seen.
      3. Inverted Pyramid of Numbers: The number of individuals in this pyramid rises from the lowest to the highest trophic level. There will be a limited number of major producers in a forest, for example, a few numbers of huge trees.
      4. It can be attributed to the fact that the tree (primary producer) is few and thus represents the base of the pyramid, followed by dependent herbivores (for example, birds). In the next higher trophic stage, and parasites in the next trophic level. Hyper parasites being at higher trophic levels represent higher numbers.
      5. Pyramid of biomass: Individuals in each trophic stage are weighted rather than counted like a pyramid of numbers. This yields a biomass pyramid or the total dry weight of all species at each trophic stage at any given time.
      6. At each trophic stage, this reflects the total standing crop biomass. The sum of living matter in a crop at any given time is referred to as standing biomass. It is represented as gm/unit area or Ki local/unit area. The biomass pyramid is upright in many terrestrial ecosystems.
      7. Although in an aquatic environment, the biomass pyramid can be inverted; for example, in a pond, phytoplankton is the primary producer, with short life cycles and a high turnover rate (i.e., they are rapidly replaced by new plants). As a result, their overall biomass is less than the biomass of herbivores they sustain at any given time.
         1. Upward Biomass Pyramid: The biomass pyramid in most terrestrial ecosystems has a broad base of primary producers with a smaller trophic level perched on top.
         2. Inverted Biomass Pyramid: In many aquatic environments, the biomass pyramid can take on an inverted shape. Since the producers are tiny phytoplankton that develops and reproduce quickly, this is the case.

Pyramid of Biomass

1. Pyramid of Energy: Since energy flows from one trophic stage to the next, energy is always lost as heat at each step, the pyramid of energy is always upright and can never be inverted.
2. The total amount of energy at each trophic level is represented by this pyramid. Energy is indicated using units like Cal/unit area/unit time or kcal/unit area /unit time.
3. The biological magnification phenomenon—the propensity for harmful compounds to accumulate at higher levels of the food chain—can be explained using the energy pyramid definition.

Conclusion:

An ecosystem’s energy flow is the synergy of the flow of energy from the producers, to the consumer down the chain of consumption. This flow of energy helps in the maintenance of a sustainable cycle of Energy in the Ecosystem