What Are Food Chains?

A food chain represents the flow energy and nutrients through ecosystems, from start to end. It tells us how each organism in the ecosystem obtains the energy required for it to survive. At times, organisms may have a co-dependent relationship with other organisms, other times they would consume them.

It is the relationships that each organism has that allows the ecosystem to thrive. Should any part of the food chain be disrupted, the ecosystem could well collapse. As such, it is important for us to understand the intricacies of a food chain and to ensure that it is never disrupted irreversibly.

Types of Organisms in a Food Chain

Within a single ecosystem lies a range of different organisms, each with its own method of obtaining energy. As such, a food chain is akin to an energy pathway, within which nutrients flow from producers to consumers.

Before diving further into the various roles of organisms, we first need to recognise the different types of organisms in a food chain. For nutrients to flow, producers known as autotrophs need to exist within the ecosystem.

Autotrophs are capable of making their own food from simple molecules, and thus are the start of any food chain. There are two basic types of autotrophs – photoautotrophs & chemoautotrophs.

Photoautotrophs

Plants are an example of photoautotrophs. With the help of sunlight, they combine carbon dioxide and water to make sugars during photosynthesis. Most plants do not require the consumption of other organisms in order to attain energy.

Chemoautotrophs

Chemoautotrophs describe organisms that convert carbon-containing molecules into organic matter using the oxidation of inorganic compounds as an energy source. Commonly, organisms that carry out chemosynthesis do it in the absence of sunlight.

Autotrophs are the foundation of every ecosystem on earth and allow feeder organisms to survive. These feeder organisms are known as heterotrophs.

Heterotrophs

Most organisms, such as mammals, fish, reptiles and birds are incapable of making their own food out of inorganic matter. Rather, they attain their organic molecules through the consumption of other organisms. Yet, consumers also fill different ecological roles, ranging from plant-eating insects to meat-eating animals.

Analysing a Typical Food Chain

A food chain is a sequence of organisms through which both energy and nutrients travel. A typical food chain starts with producers and then moves onto the various types of consumers. An example would be:

• Base of the food chain – autotrophs are the primary producers that convert inorganic matter into organic substances.
• Second layer – primary consumers, which are typically herbivores that consume plants, algae and bacteria for food.
• Third layer – secondary consumers, which are carnivores who prey on herbivores
• Fourth layer – tertiary consumers, which are carnivore-eating carnivores

The Complexity of Food Chains

Depending on the organisms in the environment, many additional layers of consumers can exist with the top consumer in a food chain being called the apex predator. It is also worth noting that many intersecting food chains exist within an ecosystem with many complications. For example, humans are typically the apex consumer in any food chain that they are a part of, yet being omnivores, we consume both plants and animals.

Decomposers

While not always included within food chain diagrams, decomposers always interact with the organisms in the food chain. Decomposers are organisms that break down dead organic material and their wastes. This includes decaying plants or the remains of a deceased animal.  As such, they do not have a predefined level in the food chain, but instead run parallel to its hierarchy.

Key decomposers in ecosystems would include fungi and bacteria which use the remaining chemical energy in dead matter to fuel their metabolic processes.

Detritivores

In some ecosystems, an additional layer exists between dead organisms or decomposing matter and the decomposers. Detritivores feed on dead organic matter while also helping to fragment them. This makes the dead matter more available to bacterial and fungal decomposers.

Examples of detritivores include earthworms, crabs, slugs and vultures. While not a mandatory member of a food chain, detritivores help to speed up the rate of decomposition and thus the renewal of the food chain cycle.

Decomposition & Decay

It is important to recognise that the earth does not have infinite resources for organisms to consume. Rather it requires replenishment, which occurs through decomposition. When dead matter is broken down through decomposition, its nutrients are released back to earth. These simpler organic forms serve as the food source for primary producers, thus renewing the food chain again.

Ecosystem Limitations

All ecosystems operate under limitations and are highly fragile environments. They are unable to grow infinitely in scale and are also highly vulnerable to any foreign introduction or interference.

Energy Transfer in Food Chains

The amount of energy transferred between levels in a food chain is inefficient. This is because the only energy that is available for the next level of consumers is the stored biomass in the previous level of organisms.

It is estimated that only about 10% of the energy stored is available to be passed on. Since there is a limit of 10% on energy transfer, food chain lengths are thus capped between 3 to 6 levels. A food chain would simply be unable to sustain additional levels as there would be insufficient energy to pass on.

Disruptions to Food Chains

A disruption to a food chain occurs when a new predator is introduced or a change in the environment causes a level in the food chain to be severely diminished. In both cases, the result can be highly unpredictable as organisms need to readjust to the change in available energy levels. It is thus possible for entire populations of a certain organism to be wiped out over a period of time. On the other hand, other organisms may start to thrive.

An example of the diverse effects of disruptions to food chains and thus the ecosystem is as follows:

• Overhunting by humans of apex predators such as wolves
• Herbivores, which without the threat of apex predators, start to thrive
• Plant life in the ecosystem starts to decline as a result of increased herbivore numbers
• The ecosystem is devastated by the overconsumption of plants by herbivores

The Importance of Understanding a Food Chain

As covered in this article, ecosystems can change drastically with a single action. The mere introduction of a new consumer into the ecosystem can change entire food chains. It is thus important that we comprehend how an ecosystem works and the consequences of interfering with it.

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