Food and Energy: Energy Transfer and Ecological Pyramids

Edited by Jamie (ScienceAid Editor), Jen Moreau, Carlos Spicy Wiener, SarMal and 2 others

You've probably studied food chains since primary school and are familiar enough with the concept to differentiate between herbivores and carnivores to identify those species at the top of the food chain and those species on the bottom. These concepts are the rudimentary basics of the food chain, however, food chains can be much more intricate and are undoubtedly vital parts of our ecosystems. As the name implies, food chains link the consumption of food, the amount of energy wasted and the transfer of energy amongst a species. Food chains always start with a plant source and always end with an animal. A simple example of a food chain would be: a plant is consumed by a herbivore, the herbivore is then consumed by a carnivore. Seems pretty simple right? It is, but there are many more links and transference of energy depending on the food chain.

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Food Chains

A typical food chain looks like this:

a food chain involving grass, a rabbit and fox

A food chain the transference of energy between organisms through consumption, in this case, the rabbit is eating grass and the fox is eating the rabbit.

The initial energy source is found in the plant. The plant uses initial energy from the sun to convert into chemical energy via photosynthesis. The herbivores eat the plants, ingesting some of the energy from the plant of the energy. The herbivore then becomes prey their energy is transferred to the predator.

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When consumed some of the energy is transferred but some of the energy is lost at each link in the chair (or trophic level). In the above example, the grass loses some energy by respiration, the rabbit loses energy by heat and waste. By the time the energy is transferred to the fox, there is only a fraction of the total energy transferred.

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Energy Transfer

In each ecosystem, it is energy, that enables organisms to live. This energy mainly comes from one original source: photosynthesis. The plants in the ecosystem use this solar energy to produce carbohydrates which are then consumed by other organisms: transferring the energy.

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Not all of the energy from sunlight, however, is used by the plants solely as energy; they are far from efficient. A lot of sunlight misses the plant, is in the wrong wavelength or lost in the inefficiencies of photosynthesis. We use the term gross primary production to refer to the total energy in the molecules of the plant; net primary production is the surplus energy not used by the plant itself.

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At each level of the food chain energy is lost because it is used by the organism itself for respiration. This limits the number of steps there can be in a food chain.

diagram representing energy transfer in a food chain

The diagram above represents quantitatively (in numbers) the efficiency of energy transfer in a food chain. Notice that only about 8% of the energy is transferred from one stage to the next.

Ecological Pyramids

A food chain is represented quantitatively (with numbers) in the form of a pyramid of number. Listed below is a quantitative representation of the previously presented food chain. From this graph, we can see there are fewer foxes than rabbits; which makes sense because a fox must eat several rabbits to get enough energy in order to survive.

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An ecological pyramid shows the relative sizes of different components at the various trophic levels of a food chain. A trophic level refers to each stage (shown as a horizontal bar on ecological pyramids). There are three types of ecological pyramid we use: numbers, biomass and energy.

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pyramids of energy, biomass, and numbers for two different food chains

The pyramids of numbers show the raw number of each species at each trophic level. The top example is a typical food chain with a large number of producers but diminishing numbers of consumers. However, if the producer was a tree, followed by insects, then the bottom bar would appear small as many organisms feed on one tree. In this instance, the pyramid of biomass is more useful as the tree is much larger.

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In the lower example, both the pyramid of numbers and biomass show a smaller producer bar; given what was discussed under the previous heading - this does not make sense. This is because the phytoplankton reproduces very quickly. However, when we represent this information in a pyramid of energy we get a true pyramid.

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Plotting the energy will always give a true pyramid because it is impossible to create new energy. A trophic level will always be smaller than the one below it.

The picture of grass in the first graphic was taken by Catarina Carvalho and taken from wikimedia commons

Questions and Answers

How does energy transfer through the number, energy, and biomass pyramids?

How does the energy transfer through all these pyramids. The article dossn't say how energy transfer through number, energy, and biomass pyramids

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Why is the energy conversion factor different for caterpillar (5.5 kcal/g) vs. the food (4.35 kcal/g)?

I had to calculate the energy for both the caterpillar and food in my experiment

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Chicago / Turabian "Food and Energy: Energy Transfer and Ecological Pyramids." Accessed Apr 29, 2017.

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Categories : Ecology

Recent edits by: Sharingknowledge, SarMal, Carlos Spicy Wiener

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