Ecosystem Dynamics: Food Chains and Energy Flow

Food Chains and Trophic Networks

Food chains: A food chain is formed by a number of organisms linearly ordered, so that each of them is the food for the organism that follows in the sequence. For instance, algae are producers that create organic matter from inorganic substances.

Trophic relationships in an ecosystem are rarely as simple as a single food chain. Instead, connections between different chains form a complex structure called a food web. A food web is the set of interconnected food chains within an ecosystem.

Energy Dynamics in the Food Chain

Energy in the food chain: Producers capture only a portion of the light energy from the Sun that reaches the Earth's surface. This energy is utilized for photosynthesis to produce organic compounds from inorganic matter. What happens to the rest of the organic matter produced during photosynthesis?

• Part of it degrades through respiration.
• Another part is lost when organisms die.
• The remainder is stored within the active bodies of the organisms.

Flow of Matter and Energy in Ecosystems

Matter cycles through the ecosystem: inorganic compounds from the environment are transformed into organic matter by photosynthesis, and finally returned to the environment by the action of decomposers, where they can be reused by producers.

In contrast, solar energy, stored and processed by plants into organic matter, is eventually released into the environment as heat and cannot be reused by living organisms.

Ecosystem Production and Biomass

The production of an ecosystem: A portion of the energy that passes through a trophic level is stored by organisms in the form of biomass. Production refers to the increase in biomass of an ecosystem or one of its trophic levels per unit of time.

There are various ways to measure production, such as kilograms per square meter. Key metrics include:

• Net primary production
• Net secondary production

Ecological Pyramids and Trophic Levels

These graphical representations demonstrate how characteristics like production or biomass vary between trophic levels.

Energy Production Pyramids

In an energy pyramid, each rectangle represents the energy stored in that trophic level during a specific time. In these pyramids, the largest rectangle represents the producers, with subsequent levels for consumers becoming progressively smaller.

Biomass Pyramids

Biomass pyramids are constructed using data from the biomass of each trophic level. These pyramids can be inverted when the biomass of a higher level exceeds that of a lower level.

Pyramids of Numbers

The pyramids of numbers reflect the total number of individuals at each trophic level. In some cases, these can also be inverted.