Trophic level

 

Introduction

  • In ecology, a trophic level pertains to a position in a food chain or ecological pyramid occupied by a group of organisms with similar feeding modes
  • The trophic level of an organism is the number of steps it is from the start of the chain
  • The concept of trophic level was developed by Raymond Lindeman (1942), based on the terminology of August Thienemann (1926)
  • The trophic levels are shown in a series or a succession to represent the flow of food energy and the feeding relationships between them

 

Categories

  • The trophic levels have two major categories: the autotrophs and the heterotrophs
  • Autotrophs are organisms that can produce organic matter from inorganic matter.
    • Since they can make their own food and do not need to feed on other organisms, they are also referred to as the producers of an ecosystem
  • Heterotrophs are organisms that obtain organic matter directly by consumption
    • Unlike autotrophs, they do not have the ability to manufacture their food from inorganic sources. Thus, they hunt or gather food from other organisms. Hence, these are referred to as consumers
    • Heterotrophs may be further grouped as:
      • Primary Consumers: These comprise the plant-eating organisms called herbivores
      • Secondary Consumers: These feed on the primary consumers
      • Tertiary Consumers: These feed on the secondary consumers and so on
      • Final Consumers: The final group called reducers feeds on dead organic matter. They include the detritivores and the decomposers

 

Trophic Structure

    • Trophic structure refers to the partitioning of biomass between different trophic levels.
      • It is controlled chiefly by the biomass of the primary producers
    • The primary producers affect the transfer efficiency between trophic levels as they essentially provide the energy and the nutrient inputs
    • Apart from them, another important factor is the top-down component.
      • This includes the predators.
      • Their consumption suppresses the lower trophic levels.
      • In a way, the predators help the primary producers by controlling or limiting excessive herbivory by predation. They serve as biological control of the lower trophic levels

 

Trophic Level Pyramid

    • An ecological pyramid is often depicted as a trophic level pyramid.
      • It is a graphical representation in the shape of a pyramid comprised of plants and animals in a certain ecosystem
    • The shape indicates that the bottom trophic level is comprised of organisms that can make their own food through available sources from the environment.
      • They do not feed on other organisms to obtain their nutritional requirements.
      • Thus, they represent the base. This portion of the pyramid is comprised of producers.
    • As the trophic levels go up, it tapers towards the peak.
      • This pyramid shape depicts the biomass in each trophic level.
      • Biomass is the amount of living or organic matter in an organism. The base shows the largest biomass and then diminishes in amount as it moves up to the apex. This is the most common structure in ecosystems
    • However, there are also instances wherein an inverted pyramid occurs.
      • The latter results when the combined weight of producers is smaller than the combined weight of consumers

energy_pyramid

 

Trophic level examples

    • Level 1: producers
      • This level comprises the primary producers, and are found the base of an ecological pyramid
      • They are found at the base of an ecological pyramid
      • The fundamental feature of organisms in trophic level 1 is their ability to produce their own food from abiotic materials
    • Level 2: primary consumers
      • In this level, the organisms occupying this level feed on the primary producers and are called primary consumers.
      • Animals that feed on plant materials are called herbivores
      • They have anatomical and physiological features that make them adapt to a plant diet
      • Examples of herbivores are horses, cattle, and goats
    • Level 3: secondary consumers
      • Secondary consumers are comprised of animals that feed on primary consumers. Organisms that eat other animals are called carnivores (or predators)
      • Predation is an interaction in an ecosystem where a predator hunts or catches, kills and eats prey. Thus, Predators are in turn, adapted anatomically and physiologically for an animal diet
        • Examples of animals with a predator-prey relationship are spiders and flies, lion and zebra, bear and fish, and fox and rabbit
      • Not all predators though have a diet exclusive of meat. Their diet may also include plant materials. Animals that feed on both plants and animals are called omnivores
        • Examples of omnivores are chimpanzees, orangutans, gorillas, pigs, most bears, etc.
      • Other trophic levels
        • The organism that feeds on a secondary consumer is called a tertiary consumer and the one that eats on a tertiary consumer is referred to as a quaternary consumer.
        • The tertiary consumers and the quaternary consumers occupy trophic levels 4 and 5, respectively
      • Decomposers
        • The last of the trophic level is occupied by decomposers, such as detritivores. They feed on dead plants and animal matter.
        • Detritivores are decomposers that specifically fragment to consume their food.
        • Examples of detritivores are worms, millipedes, dung flies, woodlice, and slugs. Other decomposers include fungi and bacteria