Trophic level

Living things are part of a food web.

Plants are at the first level. They make their own food from sunlight.

Next, some animals eat the plants. These are called herbivores. Other animals eat those animals. These are called carnivores.

Some animals eat both plants and meat. These are called omnivores. Humans eat both, too.

Finally, tiny things break down dead matter. They turn it into food for plants. This keeps the web going.

Every living thing has a place in nature. This place is called a trophic level. You can think of these levels as steps in a food chain.

Level 1 starts with primary producers. These are plants and algae. They use sunlight to make their own food. This is called photosynthesis.

Level 2 is for herbivores. These animals eat the plants. Level 3 is for carnivores. These animals eat the herbivores. Some animals eat both plants and meat. We call these omnivores. Humans are omnivores. Our average level is about 2.21. This is close to the level of a pig.

At the top are apex predators. These animals have no predators of their own. They sit at the highest levels.

Energy moves up these levels. We can show this with an energy pyramid.

Only about 10% of energy moves to the next step. This is why food chains are usually short. Decomposers like fungi help too. They break down dead things. They turn waste back into nutrients for plants.

Every living thing has a specific place in nature. This position is called a trophic level. The word trophic comes from a Greek word for food or nourishment. You can think of these levels as steps in a food chain. A food chain is a line of living things that eat each other. Most food chains are actually part of a larger food web. A food web is a complex network of many overlapping chains.

Nature works in a very organized way to move energy. It starts at level 1 with primary producers. These are mostly plants and algae. They use sunlight to make their own food through photosynthesis. In the deep sea where there is no light, they use chemosynthesis instead. Next come the consumers at level 2. These are herbivores that eat the plants. Level 3 includes carnivores that eat the herbivores. Higher levels include tertiary consumers and apex predators. Apex predators are at the very top and have no predators of their own.

Scientists have studied these levels for a long time. Raymond Lindeman developed the concept of trophic levels in 1942. He built his work on ideas from August Thienemann in 1926. Thienemann used terms like producers and consumers. Lindeman later changed the word reducers to decomposers. Decomposers like fungi and bacteria break down dead matter. They turn waste into nutrients that plants can use again. This recycling helps the whole ecosystem stay healthy.

Energy moves through these levels in a specific way. We can picture this using an energy pyramid. Only about 10% of the energy moves from one level to the next. This is known as the ten per cent law. Because so much energy is lost, food chains are usually short. They rarely go past 5 or 6 levels. Most plants turn only 1% of sunlight into energy. This means very little energy reaches the highest predators.

Sometimes the levels are not simple whole numbers. Many animals eat more than one kind of food. This gives them a fractional trophic level. For example, humans have an average level of 2.21. This is similar to the level of a pig or an anchovy. However, some people like the Inuit eat mostly seals. This puts their trophic level near 5. Even large animals like orcas can have different levels based on what they hunt.

In every ecosystem, living things occupy specific positions based on how they obtain nourishment. These positions are known as trophic levels. The term "trophic" comes from the Greek word *trophē*, which means food or nourishment. Trophic levels help scientists organize the complex ways energy moves through a food web. A food web is a large, intricate network of many overlapping food chains. Within these webs, a food chain is a simple succession of organisms eating one another.

Energy enters most ecosystems through primary producers, which sit at trophic level 1. These organisms, such as plants and algae, are also called autotrophs. They manufacture their own food through photosynthesis, using energy from the sun. In deep-sea hydrothermal ecosystems where sunlight cannot reach, producers use a different process called chemosynthesis. These producers pull nutrients from the soil or water to build their own organic matter. This process forms the essential base that supports all other life in the chain.

Consumers, or heterotrophs, must eat other organisms to survive. They are categorized by what they eat. Herbivores are primary consumers that eat plants at level 2. Carnivores that eat herbivores are secondary consumers at level 3. Carnivores that eat other carnivores are tertiary consumers at level 4. Some animals are omnivores, meaning they eat both plants and animals. At the very top, apex predators occupy the highest numbered levels. A healthy adult apex predator has no natural predators of its own.

Decomposers, also called detritivores, play a vital role in recycling. Organisms like bacteria and fungi break down dead plant material, animal remains, and waste. They convert this matter into inorganic chemicals. These chemicals act as mineral nutrients that plants can use again. While decomposers are often left off food web diagrams, they effectively mark the end of a food chain. Because they return nutrients to the producers, some scientists view them as occupying their own unique trophic level.

The movement of energy between these levels is often visualized using an energy pyramid. This diagram shows how much energy is required to support each successive level. This relationship is governed by the ten percent law, or ecological efficiency. On average, consumers convert only about 10% of the chemical energy in their food into their own organic tissue. This means most energy is lost as it moves up the chain. Because of this low efficiency, food chains rarely extend beyond 5 or 6 levels.

Historically, the concept of trophic levels was refined by scientists over many years. Raymond Lindeman developed the modern concept in 1942. He built his work upon terminology used by August Thienemann in 1926. Thienemann originally used the terms "producers," "consumers," and "reducers." Lindeman later modified the term "reducers" to the more common word "decomposers." This scientific framework allows us to measure the health and complexity of different ecological communities.

Trophic levels are not always simple whole numbers because many animals have diverse diets. This results in fractional trophic levels. For example, a mountain lion might eat both rabbits and bobcats, placing it at different levels depending on the meal. Scientists can calculate these fractions using the weighted average of an organism's diet. Humans have an average trophic level of 2.21, similar to pigs. However, a traditional Inuit diet of seals can result in a trophic level near 5.

Understanding these levels is critical for managing global resources like fisheries. In some areas, the mean trophic level of the catch has declined. This happens when high-trophic-level fish, like tuna, are overfished. This process is sometimes called "fishing down the food web." When large predators disappear, fishing fleets often shift toward smaller, lower-trophic-level species like shrimp or herring. Monitoring these levels helps scientists understand how human activity changes the balance of entire marine ecosystems.