Understanding Trophic Levels, Food Chains, and Energy Flow in Ecosystems

Posted on Aug 24, 2024 in Biology

Trophic Levels in Ecosystems

A trophic level consists of all the organisms in an ecosystem that feed in the same way. There are three main types:

Producers

Autotrophic organisms that perform photosynthesis and use solar energy to transform inorganic matter into organic matter.

Consumers

Heterotrophic organisms that eat other living things:

Primary consumers: Feed on producers; they are herbivores (e.g., rabbits, deer).
Secondary consumers: Feed on primary consumers (e.g., frogs feed on insects).
Tertiary consumers: Feed on secondary consumers (e.g., lions, tigers).

Decomposers

Heterotrophic organisms that obtain their nutrients by decomposing dead organisms (like bacteria and fungi).

Food Chains and Food Webs

Food Chain

A trophic chain, or food chain, is a diagram that uses arrows and drawings to show the organisms in the different trophic levels of an ecosystem and their feeding relationships.

Food Web

Trophic networks, or food webs, are representations of the different trophic chains in an ecosystem and the connections between them.

Transfer of Matter and Energy

Transfer of Matter

Producers create organic matter: Producers take inorganic matter (carbon dioxide, water, and mineral salts) and transform it into organic matter to build and repair their bodies.
Organic matter passes through the trophic levels: Organic matter is transferred to the primary consumers when they eat the producers, then to the secondary consumers, and so on. Consumers use this organic matter to build and repair their bodies.
Organic matter returns to the environment: When organisms die, decomposers feed on them and transform organic remains into products that return to the environment and are used by the producers.

Transfer of Energy

Producers capture part of the solar energy: Most of the energy ecosystems receive comes from the sun. Producers only use a part of it to perform photosynthesis, where light energy is transformed into chemical energy and stored in the organic matter they produce.
Energy flow through trophic levels: The energy is passed through food. Most of the energy is consumed by metabolism, and some is released as heat at each trophic level.

Trophic Parameters

These parameters allow us to assess the matter and energy that accumulates at each trophic level and passes from one level to another.

Biomass

Biomass is the amount of organic matter created in each trophic level of the ecosystem and can be used as an energy resource.

Types of biomass:

Primary biomass: Produced by autotrophic organisms (photosynthesizing organisms).
Secondary biomass: Produced by heterotrophic organisms (animals, fungi, etc.).
Tertiary biomass: Formed as a result of human activity, such as sawdust (primary) or manure and urban waste (secondary).

Production

Production is an increase in the biomass of an ecosystem, or one of its trophic levels, per unit of surface area or volume, and per unit of time. It’s a measurement of the amount of energy that accumulates in the ecosystem or each trophic level.

Primary production: The amount of light energy established as primary biomass by photosynthesizing organisms.
Gross primary production: The total amount of organic matter (biomass) synthesized by autotrophic organisms per unit of time, including that consumed by respiration, metabolism, and reproduction.
Net primary production: The organic matter that remains after deducting respiration.
Secondary production: The amount of energy stored in the tissues of heterotrophic organisms.
Gross secondary production: The percentage of the total amount of food consumed that is assimilated.
Net secondary production: The energy that remains available for the following trophic level.

Ecological Pyramids

Ecological pyramids, or trophic pyramids, are graphs that provide a simplified version of the trophic relationships between organisms in a biological community. They allow us to quantify biomass, energy available, and the number of individuals in the community.

Energy pyramids: Show the energy available in each trophic level.
Biomass pyramids: Provide information about the organic matter accumulated in each trophic level per unit of surface area at a specific time.
Number pyramids: Show the number of individuals found in an ecosystem per unit of surface area or volume at a specific time.

Biogeochemical Cycles

A biochemical cycle is the circulation of chemical elements through the atmosphere, hydrosphere, geosphere, and biosphere, making these elements available repeatedly.

Types of biogeochemical cycles:

Gaseous nutrient cycles: The atmosphere is the main reserve of the element (e.g., oxygen, carbon, and nitrogen cycles).
Sedimentary nutrient cycles: The main deposit of the element is the lithosphere (e.g., sulfur and phosphorus cycles).

The Carbon Cycle

The carbon cycle can be summarized as two sub-cycles:

The short cycle: Living things capture and transform CO₂ found in the atmosphere and dissolved in the hydrosphere. Producers use photosynthesis to “fix” CO₂ into organic matter. Consumers and decomposers incorporate this carbon into their bodies through the food chain. When organisms respire and die, and decomposers act on their organic matter, most of the carbon returns to the environment.
The long cycle: Relates to the carbon stored in fossil fuels, limestone, wood in trees, and inside the Earth. This carbon can return to the atmosphere after millions of years through the burning of fossil fuels, weathering of limestone, burning of wood, and volcanic eruptions.