What are Trophic Levels?

In ecology, food chains refer to the transfer of energy and matter as they pass from one organism to another. Additionally, they take into account the energy that is lost at each level. This energy is lost through various processes, such as respiration. Terrestrial food chains are concerned with this transfer of energy among terrestrial organisms. This means plant and animal species that carry out their vital functions on land, not in aquatic environments.

Energy generally moves from producers to consumers, and some is lost at every transfer. As a result, less energy is usually available at higher trophic levels, which helps explain why food webs often support fewer top predators.

A trophic level is the level at which a given organism resides on a food chain. The trophic level of one organism depends on how it relates to other organisms within the same food chain. Within a terrestrial food chain, we can find:

• Producer organisms: individuals, usually plants, that transform inorganic matter into organic matter. They are the beings that initiate the chain.
• Primary consumers: these are the animals that feed on whole producer organisms or some of their parts. These parts may include leaves, roots, seeds or fruits. In general, they are herbivorous animals, although omnivorous animals also eat plants.
• Secondary consumers or mesopredators: these are predatory animals that hunt and feed on primary consumers, or herbivores. Therefore, they are carnivorous animals.
• Tertiary or super-predatory consumers: these animals can feed on secondary consumers and, in some cases, on organisms at lower trophic levels. They are important in ecosystems since some act as "umbrella" species. These are organisms whose protection can help conserve their habitats and the other species associated with them.

In ecosystems, there are no simple trophic chains with just one individual at each level. Instead, there is a complicated system of interactions where many chains are related to each other in various ways. This is why trophic chains link together to form what is known as a "trophic network".

Decomposers, such as fungi and bacteria, break down dead organisms and waste, returning nutrients to the environment. They are important to these systems, although they are not always shown as a single step in a food chain.

Each ecosystem has its own trophic levels, formed by the animals and plants that live in a given biome. A trophic chain of a terrestrial ecosystem differs from an aquatic trophic chain in that the latter is formed by beings that inhabit aquatic environments. The former, as we have said, are those that live on land.

Occasionally, aquatic and terrestrial food chains can link to the same trophic network. This means aquatic organisms may feed on terrestrial ones and vice versa. For example, the common kingfisher (Alcedo atthis), which is part of the terrestrial food chain, also feeds on small fish that live in an aquatic environment. An example of the opposite would be the archerfish (Toxotes sp.), an aquatic animal that consumes insects that fly over the water or land on surrounding vegetation.

These links show that the boundaries between land and water ecosystems are not always completely separate: feeding relationships can move energy between the two environments.

The examples of trophic levels in terrestrial food chains (or, more precisely, food webs) are practically countless. In addition, new relationships are discovered almost daily as studies in different ecologies develop. Next, we show you two examples of terrestrial trophic-level interactions in food chains:

Example 1

Pot marigold (Calendula officinalis) > European honey bee (Apis mellifera) > European bee-eater (Merops apiaster) > Red fox (Vulpes vulpes)

In this example of trophic levels in a terrestrial food chain, the marigold is the producing organism. The bee only feeds on the pollen and nectar of the flower. The bee-eater is a bird specialized in hunting bees, although other insects can also become prey for it. Finally, the red fox, although it does not hunt adult specimens, attacks the nests these birds build on the ground, preying on the eggs and hatchlings for sustenance.

Example 2

Sitka spruce (Picea sitchensis) > Alaska moose (Alces alces gigas) > Arctic fox (Vulpes lagopus) > Gray wolf (Canis lupus)

The Sitka spruce is a conifer whose seed cones serve as food for Alaska moose. The moose is not directly hunted by the Arctic fox, but Arctic foxes are known to scavenge for carrion (i.e. eat the remains of a deceased moose). The gray wolf is a super predator that habitually preys on both moose and Arctic foxes.

In these examples, the arrows show the direction in which energy moves, from the food source to the consumer. Real food webs can include several feeding relationships for each species, so a single chain is only a simplified view of the connections in an ecosystem.

If you want to read similar articles to What are Trophic Levels?, we recommend you visit our Facts about the animal kingdom category.