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Unit 1: Basic Ecological Concepts and Principles Related to Agricultural Systems

Energy Flow
Each organism in an ecosystem needs a regular supply of energy to grow and reproduce. The source of this energy is, of course, sunlight. Plants capture solar energy and store it in the form of plant biomass (leaves, shoots, roots, fruits, seeds). Because of the key role plants play in capturing and storing energy, ecologists call them primary producers. Herbivores in turn consume plants for their own growth, and predators and parasites that prey on herbivores or other consumers continue the conversion process. Let’s look at how this process works in more detail. Click the diagram to the right to enlarge:


Energy flow in ecosystems showing relative amounts of energy flowing through different trophic levels.

On average, only about 10% of the energy is transferred from one trophic level to the next. The majority of the energy that enters an ecosystem is eventually lost as heat. Think about how this energy flow diagram would look for agroecosystems. How many trophic levels would there be in a vegetable farm? How many levels in a grass-fed beef operation?
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