Trophic Relationships and Energy Flow in Ecosystems

Trophic Relationships

Organisms in an ecosystem are grouped according to how they obtain energy and matter:

• Producers: these are autotrophic organisms. They make their own organic matter from inorganic matter.
• Consumers: these organisms feed on other living organisms. Several types of consumers exist:
  • Herbivores, also called primary consumers.
  • Carnivores, which are tertiary and secondary consumers. They may also be quaternary.
  • Omnivores, which eat both plants and animals.
• Decomposers: these heterotrophic organisms feed on detritus (remains of dead organisms and excrements) and transform it into inorganic compounds. Some small animals are detritivores: although they do not complete the transformation of detritus into inorganic matter, their action prepares it for the final work of the decomposers.

Food Chains and Trophic Levels

A food chain is the linear sequence of organisms in which each one is eaten by the next. All the links in a food chain are trophic levels. The first level is always formed by producers, the second level by herbivorous consumers, and the higher levels by carnivorous consumers. Each level is determined by the chain considered.

In an ecosystem, trophic relationships are not simple chains. A herbivorous animal feeds on several sources and is eaten by different carnivores. For this reason, these connections form a food web, a network of interconnected trophic chains.

Energy Transfer Between Trophic Levels

Producers store part of the energy they capture through photosynthesis as organic matter. Some of this energy is degraded during cellular respiration and used in the vital functions of the organism, and is returned to the environment as heat. Another part passes to dead organisms and waste products, which are used directly by decomposers. The rest is stored in the organs of the producers and can be consumed by the next trophic level. In the end, only a fraction of the organic matter stored by producers is transformed into the organic matter of primary consumers.

Matter and Energy Flow in the Ecosystem

In an ecosystem, matter circulates cyclically: inorganic matter is transformed into organic matter through photosynthesis, and finally returns to the environment as inorganic matter, which can again be used by producers.

Solar energy, captured and stored by plants as organic matter, is ultimately dissipated into the environment as heat and cannot be reused by living beings.