Trophic Relations and Energy Flow in Ecosystems

Trophic Relations in the Ecosystem

To study the relationships established in an ecosystem, different graphical models are used:

• Food chains
• Ecological pyramids
• Food webs

Food Chains

A food chain represents the linear transfer of matter and energy between organisms. During the transfer from one link to another, much of the available energy is lost, which is why we often observe only 3 to 5 links. There are two primary types:

• Grazing food chain: Starts with a green plant, where matter and energy pass to herbivores and then to carnivorous predators.
• Detritus food chain: Based on accumulated organic waste, such as sediments in aquatic ecosystems or the ground in terrestrial ecosystems. Detritivores feed on this detritus and serve as the lifeblood for predators.

Food Webs

Food chains are interrelated, as a single species often provides food to more than one predator. This complex network is known as a food web. The following rules apply to all ecosystems:

• Different species are grouped into trophic levels according to their ecological niche.
• A species may be consumed by several species at different trophic levels.
• A species may feed on organisms belonging to more than one trophic level.

The elimination of a species or a group of species from one trophic level can have serious consequences for the entire community. Knowledge of an ecosystem's food web is essential for assessing its ecological condition.

Ecological Pyramids

Each step in an ecological pyramid occupies a specific trophic level, with the base occupied by producers. There are three main types:

Pyramid of Numbers

Each step is proportional to the total number of individuals in the different species that make up each trophic level. In some terrestrial ecosystems, this can appear as an inverted pyramid and is often not useful for comparing ecosystems.

Biomass Pyramid

This represents the total amount of biological mass, expressed in units such as t/km², kg/ha, or g/m².

Pyramids of Energy

Each step represents the amount of biomass or energy produced per unit of time. These are expressed as:

• Biomass units: t/km²/year, kg/ha/year, or g/m²/year.
• Energy units: Kcal/m²/year or cal/cm²/year.

These pyramids quantify the production of biomass or energy available at each trophic level, providing a clear picture of trophic relationships and the efficiency of energy transfer between levels over time.