The trophic structure of an ecosystem describes the hierarchical levels of food chains that illustrate the flow of energy and nutrients within that ecosystem.

More specifically, the trophic structure outlines the relationships between different organisms based on their feeding behaviors. This structure is organized hierarchically, with each level referred to as a trophic level. Essentially, it represents the interactions of who consumes whom and how energy and nutrients are transferred throughout the ecosystem.

At the foundational level of the trophic structure are the producers, also known as autotrophs. These organisms can synthesize their own food through processes such as photosynthesis or chemosynthesis. Examples of producers include plants, algae, and certain bacteria, which convert energy from sunlight or chemical reactions into organic matter that serves as food for other organisms.

The next tier comprises the primary consumers, or herbivores. These organisms feed on the producers, deriving energy and nutrients from them. Common examples of primary consumers include rabbits, cows, and caterpillars.

Above the primary consumers are the secondary consumers. These are typically carnivorous animals that prey on primary consumers. Examples of secondary consumers include wolves, lions, and various birds of prey. Some secondary consumers are omnivores, meaning they consume both plants and animals.

The subsequent level consists of tertiary consumers, which are usually top predators that feed on secondary consumers. Notable examples of tertiary consumers include eagles, sharks, and humans.

At the apex of the trophic structure are the decomposers, also referred to as detritivores. These organisms play a crucial role in breaking down dead organic material and waste products, thereby returning essential nutrients to the soil for use by producers. Examples of decomposers include fungi, bacteria, and earthworms.

It is important to note that each transition up the trophic structure involves a loss of energy; only a fraction of the energy consumed at one level is transferred to the next. This phenomenon is often illustrated by the 10% rule, which states that typically only about $10\%$ of the energy from one trophic level is available to the next. This energy loss constrains the number of trophic levels that an ecosystem can sustain.

In summary, the trophic structure of an ecosystem provides a framework for understanding the intricate web of feeding relationships and the flow of energy and nutrients throughout the system.