Energy Flow and Trophic Levels in Ecosystems

Producers and Consumers

Producers are autotrophic organisms, such as plants and algae, that fabricate their own organic matter from inorganic carbon dioxide and mineral salts.

Consumers are heterotrophic organisms that feed on living organic matter. There are different types:

• Herbivores, also called primary consumers, are animals that eat plants.
• Carnivores, or secondary consumers, feed on animals and may include herbivores.
• Third-order consumers (tertiary) and fourth-order consumers.

Decomposers and Detritivores

Decomposers are heterotrophic organisms, such as fungi and bacteria, that feed on detritus (remains of living organisms or excrement) and transform it into inorganic matter.

Detritivores are small animals, like worms or slugs; they do not achieve the complete transformation of debris into inorganic matter but prepare it for the final action of decomposers.

Trophic Chains and Food Webs

A trophic chain is formed by a number of bodies sorted linearly so that each one of them is eaten by the next. For example: phytoplankton → water flea → chub → heron.

Food webs are sets of interconnected food chains that can be established within an ecosystem.

The Fate of Organic Matter in Photosynthesis

What do producers do with the organic matter produced in photosynthesis?

• One part is degraded in respiration: the energy released to degrade organic matter in respiration is used to operate the organism and is released again as heat.
• Another part constitutes waste: dead organs like leaves or frogs.
• The rest is stored in their bodies (fruits, leaves, roots) so this matter can be used by animals.

Matter circulates in the ecosystem in a loop: inorganic compounds from the medium, transformed into organic matter in photosynthesis, are ultimately returned to the medium and can be re-used by producers.

Biomass and Energy in Ecosystems

Energy in the ecosystem is measured by biomass, which is the term used to indicate the amount of organic matter that consists of an individual, a trophic level, or an entire ecosystem. Biomass is measured in grams or kilograms and stores energy.

The increase in biomass per unit of time is called output or production, measured in kg/m²/year, tonnes/ha/year, or kJ/m²/year.

Types of Production

1. Net Primary Production (NPP): The increase in biomass production by producers.
2. Net Secondary Production (NSP): The increase of biomass in different consumer levels.
3. Net Ecosystem Production (NEP): The growth of biomass that accumulates in the ecosystem during a determined period. PNE = Photosynthesis - Respiration.

Ecological Pyramids

Ecological pyramids are forms of representation used to show multiple characteristics of trophic levels. Types include:

• Pyramids of Energy or Production: In a pyramid of energy, each rectangle represents the energy stored in that trophic level during a specific time. The rectangle for producers is always the largest and becomes smaller at the levels of consumers.
• Pyramids of Biomass: These pyramids can be reversed; for example, in aquatic ecosystems, biomass levels may exceed the level below.
• Pyramid of Numbers: Rectangles represent the number of individuals at each trophic level. These may be inverted; for example, the number of insect herbivores (consumers) can be well above the number of plants (producers).