Ecological Pyramid- Meaning ,Types

 

Introduction

  • Ecological Pyramid is a graphical depiction which is meant to illustrate the relationship between different living organisms at different trophic levels in an ecosystem
  • Each of the bars that make up the pyramid represents a different trophic level, and their order, which is based on who eats whom, represents the flow of energy
  • Energy Flow in An Ecosystem is governed by the following laws:
    • The First law of thermodynamics states that energy can neither be created nor destroyed but can be transformed from one form to another.
    • The Second law of thermodynamics states that with each successive energy transfer in a system, the amount of available energy is gradually reduced
      • For example, in an ecosystem, the transfer of food energy from one organism to another leads to the loss of a major fraction of food energy as heat due to metabolic activities. Only a small portion being stored in living tissues or biomass

Types of Ecological Pyramids

  1. Pyramid of Numbers
    • This represents the total numbers of individuals (population) present in each trophic level.
    • The term “pyramid of numbers” was first coined by Elton in 1972.
    • This pyramid is quite convenient especially when it comes to counting the number of organisms
    • This is divided into following different forms depending on the number of organisms
      1. In the Upright pyramid of numbers, the numbers of organisms mostly reduce from bottom to top.
        • It usually occurs in pond and grassland ecosystems where plants occupy the base of the pyramid.
        • The next levels of the pyramid include the consumers
      2. An inverted pyramid is actually the opposite of the upright pyramid.
        • It can closely be observed in tree ecosystem, where trees are the producers and insects are the consumers
        • The producers in the tree ecosystem are the least in numbers, and the population of consumers gradually increases at each trophic level
      3. Spindle-shaped Pyramid of Number is known as a partially upright pyramid, because there is neither sequential increase nor decrease in the number of individuals in an ecosystem
          • This type of pyramid of numbers is found in the forest ecosystem without parasites.

    • The population of higher tropic individuals usually become continuously lower because of food wastage during eating, wastage of food during digestion and finally use of food in the process of respiration and physical activities
    • Amongst the three ecosystem pyramids, the pyramid of number is the most incorrect, as it does not take into consideration the exact population.
      • Hence, it cannot completely elaborate on the trophic structure in a system
      • This pyramid ignores the biomass of species and it doesn’t show the energy transferred between individual groups
      • Pyramids of numbers are not very functional as they do not give a clear or true picture of the food chain
      • Also, They do not indicate specifically the absolute effects of the geometric, food chain, size factors of specific organisms
  2. Pyramid of Biomass
    • Biomass is the amount per unit area product of the living material existing in an individual or a number of individuals at in particular trophic level
    • This pyramid indicates the total mass of organisms in a particular trophic level
    • The pyramid is usually larger at the bottom but as it goes up it reduces in size and becomes smaller.
      • There is always a reduction of biomass with an increase in trophic level.
      • Approximately 10% to 20% of the biomass is passed from one trophic level to the other.
    • The pyramid of biomass has two forms inverted and upright pyramids
      • The aquatic ecosystem is characterized by an inverted pyramid because phytoplankton producers are located at the base of the pyramid, while consumers have larger biomass and they are located at the top
      • Upright pyramid example is the terrestrial ecosystem. It has a large base mainly consists of primary consumers, the smaller trophic levels are located at the top
    • This pyramid can be used to solve the particular issue in the pyramid of numbers because it shows the exact representation of the amount of energy present in each trophic level.
      • When there is a reduction of biomass with a rise in trophic levels, it signifies wastage and consumption of biomass at every transfer level.
    • Limitations
      • It’s actually impossible to measure the mass of every single individual. Only a sample is taken, this leads to mistakes
      • Also, the specific time of the year when data is taken should be put into consideration, since breeding seasons in different organisms differ

Upright Pyramid of Biomass & Inverted Pyramid of Biomass

  1. Pyramid of Energy
    • Pyramid of energy is an upright pyramid that illustrates the flow of energy from producers to consumers
    • It indicates the actual role played by various organisms in energy transfer. Energy pyramids indicate how much energy is required in the next trophic level as it flows upwards
    • The pyramid of energy is based on the concept of the flow of energy in a food chain proposed by Lindemann.
      • According to Lindemann’s energy flow model, “only 10% of the total energy is transferred to the successive trophic levels and creating the biomass”
      • Remaining is utilized in respiration, hunting, and other activities or is lost to the surroundings in the form of heat.
      • Hence the energy available at each trophic level is 10% of the previous level. It is called the ten percent law of energy
    • This leads to the formation of an upright pyramid of energy that is invariably formed in each ecosystem.
      • The energy is highest at the producer level and gradually decreases as it moves to the subsequent levels, including herbivores (primary consumer), carnivores (secondary, tertiary consumers)
    • An example of the pyramid of energy can be illustrated as below:

Significance of Ecological Pyramid

  • An ecological pyramid not only shows us the feeding patterns of organisms in different ecosystems, but can also give us an insight into how inefficient energy transfer is, and show the influence that a change in numbers at one trophic level can have on the trophic levels above and below it
  • Also, when data are collected over the years, the effects of the changes that take place in the environment on the organisms can be studied by comparing the data.
  • Further, If an ecosystem’s conditions are found to be worsening over the years because of pollution or overhunting by humans, action can be taken to prevent further damage and possibly reverse some of the present damage

Limitations associated with ecological Pyramid

  • Some organisms such as fungi and microorganisms have not been given specific roles in the pyramids despite the fact that they play a vital role in the ecosystem
  • These existing pyramids are only applicable to simple food chains, which sometimes do not necessarily occur naturally
  • None, of the three ecological pyramids, deliver any concept in-relation to variations in seasons and climates
  • They also lack to consider the possibility of the existence of the same species at different levels

 

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