Y-shaped model of energy flow: Who eats whom in nature

Food chain. This simple process explains so much about the beauty of natural processes. It is so complex, yet so efficient (see Biomagnification: Nature’s karma for a short recap on what is a food chain) It is modeled by nature in such a way that even if a few links are out of place, it will continue to function. One way in which it does this by interconnecting multiple food chains into a food web. I’ve written about food webs and it’s importance in Earth’s Paradox: Greater complexity, more stability.

However, food chains also come of two types. The two types differ in where the food chain starts. One starts from plants, while the other starts from dead thing……..(no, not as spooky as it sounds).

Grazing food chain

This is the food chain I’ve talked about before. It starts from plants. Herbivores (primary consumers) eat these plants and gain their energy. From them, other carnivores and omnivores gain their energy. Since the plants are living when they are eaten, they are still actively conducting photosynthesis and fixing light energy into organic matter. Therefore, this food chain directly depends on sunlight and the organic matter fixed by it.

Detritus food chain

This is a new one; it adds another layer to the complex food habits found in nature. This food chain starts from anything that is dead in an ecosystem. These dead materials also contain organic matter, and this is food for many species. Most commonly, it is the microorganisms who are the primary consumers in this food chain. They eat and decompose the dead organic matter into inorganic molecules. These microbes (or other, bigger primary consumers of the detritus food chain like ants, flies, etc) are then eaten by their predators.

This food chain can start from dead parts of plants. If a leaf falls off from a tree, it can be attacked by decomposers for food. However, even dead herbivores and carnivores are attacked by decomposers (they also have organic matter, don’t they?). So, this food chain doesn’t start from active fixing of sunlight into organic matter. It does depend on the matter produced from photosynthesis, but the relationship is indirect.

Are these two food chains connected?

Yes, they are. While grazing food chains combine to form a food web, in nature even detritus food chains enter into the mix. It adds another dimension to the flow of food (and therefore, energy) in an ecosystem. E.P. Odum (1983) identified this relationship and called it the Universal model of flow of energy. Today, it is commonly referred to as Y-shaped model.

Y-shaped model of flow of energy in ecosystems

A the flow of energy in a single food chain; either grazing or detritus, is termed the single chain model. However, in nature, that is rarely the case. Even food webs, which are more realistic representations of flow of energy is incomplete until you consider the detritus food chain as part of the food web. That is why the flow of energy is so complex; it has so many permutations and combinations.

The Y-shaped model explains the connection between a grazing and a detritus food chain. Consider this example-


In this, the upper food chain of plant—>deer—>lion is a part of the grazing food chain. The lower food chain of plant—>termite—>aardvark is a part of the detritus food chain. However, the top predator in this example, the lion, eats the deer and the aardvark. Also, when the deer and lion die, they get eaten by the termite! This shows the interlinking of the two food chains.

Theoretically, this interlinking of food chains looks like this-


You can see that at every stage, the two food chains are linked. The herbivore can be eaten by the predator of the decomposer. That predator can then be eaten by the top predator (as in the example above). Likewise, another piece of link is the fact that when the herbivore are top predator get decomposed by the decomposers when they die. (The decomposed materials are again used up by plants as nutrients. Hardly anything goes to waste!) In some ecosystems, the decomposers are also eaten by the top predators. For example, mosquito larvae in ponds are eaten by the big fishes living there.

The model is called the Y-shaped model because from the side, it looks like the letter “Y”.

This flow of energy is yet another example of how beautifully built our ecosystems are. It also underlines how changes in even one part of the chain can reverberate right through the ecosystem. 

You might also be interested in: The top-down vs bottom-up approach in an ecosystem.

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