pyramid of biomass

What Is a Biomass Pyramid?

A biomass pyramid shows the flow of energy between various levels. Producers and consumers make up the biomass pyramid, which displays all their comparative masses at the same time. To create the biomass pyramid, the approximate masses are stacked up according to a well-established hierarchy.

  1. The primary producers will lie at the bottom of the biomass pyramid. In this case, grasses, trees, flowers, and shrubs make up the needed fuel for the primary consumers that are up on the food chain.
  2. The primary consumers are herbivores: squirrels, deer, insects, and birds that feed on trees and grasses.
  3. In their turn, the primary consumers are food for the secondary consumers predators: frogs, carnivorous birds, and foxes.
  4. Finally, the tertiary consumers predators sit at the top of the biomass pyramid. In this case, a bear closes the  food chain.

pyramid of biomass

Biomass Pyramid Definition

The amount of organic matter that can be found in any living organism is called biomass. To convey the biomass present in organisms at various trophic levels, biomass pyramids will indicate the connection between the trophic level and biomass by quantifying the latter.

The quantification uses grams per meter² to represent the volume of organic matter that can be found in an ecosystem at a given time.

Food chain vs. biomass pyramid

While food chains convey the feeding relations within a certain habitat, biomass pyramids are in charge of showing the mass organisms for different levels within the food chain. However, pyramids of biomass are not a perfect representation of the energy that can be found in an ecosystem.

Their one flaw is that they can point to higher amounts of energy than there actually are. To better illustrate this, we can think of the beaks and skeletons of birds. Despite the fact that they are not eaten by consumers, they still count as mass and heavily influence the numbers.

Biomass represents the food for the higher trophic level up the food chain. At the same time, biomass has the ability to work as a renewable energy resource, decreasing the ever growing dependence on fossil fuels and helping fight off air pollution.

Energy is lost as it moves up on the food chain, which restricts the chain’s length. This is why, in the long run, plants are a more efficient way to feed people than meat. Since living organisms are in direct competition with each other over resources, predator populations are closely interrelated.

How does a food chain work?

Food chains simply keep tabs on who is eaten by whom within a given habitat. Whether we are talking about the desert or the marine environment, the same rules apply for all examples. Grass seeds feed a field mouse, which, in its turn, feeds an owl. The direction of the food chain also dictates the direction of the energy flow within the chain.

Biomass Pyramid and food chain

All food chains have two common denominators:

  • The producers –are almost invariably green plants.
  • The consumers – receive their biomass and energy from the consumption of other organisms.

The vast majority of food chains comprise up to four steps. The explanation behind this is that each step implies a loss of energy. As a result, a food chain made out of three steps will have little to no energy left for a fourth step. This also sheds some light on why the top of food chains is dominated only by a few organisms, in comparison to the lower levels that comprise more organisms.

How does a biomass pyramid work?

An organism’s biomass is made out of its total dry mass. The biomass in a given step within a food chain will always be smaller than the one from the previous step. To easily illustrate how this happens, the same food chain used above works perfectly: grass seeds are eaten by the mouse field, which is eaten by the owl.

In this case, the biomass of the grass stands at the bottom of the biomass pyramid since it has the greatest biomass in the chain. In the same vein, the owl sits on top of the pyramid, having the lowest biomass in the chain.

More complex food chains better define the underlying principles of a biomass pyramid: an oak tree feeds a caterpillar, which feeds a blue tit, which feeds a sparrow hawk.

The biomass pyramid of this four step food chain starts off with the oak tree at the bottom. The large oak tree is capable of feeding not one, but dozens of caterpillars. In a similar manner, a single caterpillar is not enough to feed a blue tit, just like a single blue tit will not be sufficient to feed the sparrow hawk.

This perfectly explains the way a biomass pyramid works, almost resembling a worksheet. The oak tree has a large biomass hence it is capable of feeding several caterpillars. The upright biomass pyramid indicates that the biomass of the organisms decreases towards the peak, ending with the significantly smaller mass of the sparrow hawk that can be found at the top of the food chain.

Biomass Pyramid

Types of ecological pyramids

The common factor in every single ecosystem is the interaction of the food chain. Better known as the “trophic structure,” this characteristic implies that most ecosystems abide by the following hierarchy: producers – herbivores – carnivores. This relation can graphically be displayed through the means of ecological pyramids.

Ecological pyramids categorize essential factors in an ecosystem: population, biomass and energy all vary and play essential roles in an ecosystem.

The way in which energy flows through any given food chain is predictable. This enters the bottom of the food chain through photosynthesis and proceeds to move up on the food chain to reach the highest trophic levels. With each transfer, there is less energy entering higher levels.

At the same time, the biomass and number of living organisms in any given ecosystem varies across trophic levels. The energy that enters specific levels directly influences the biomass and number of the organisms found in each level. A direct connection between biomass, numbers, and energy gives rise to number pyramids and biomass pyramids.

Pyramid of numbers

This type of pyramid shows the amount of individual organisms that can be found on every level. It displays the connection that links producers, herbivores, and carnivores with regard to their numbers within the successive trophic levels. For example, the base of a pyramid of numbers for grassland will be occupied by grasses, which hold the maximum number.

The number will decrease moving upward towards the apex, where the primary consumers are displayed: mice and rabbits are fewer than grasses. Moving up in the pyramid of numbers, the secondary consumers (lizards and snakes) are even lesser in number than the primary consumers.

The peak of the pyramid holds the tertiary or top consumers. They are least in number, which makes the pyramid be upright. Likewise, the ecosystem of a pond will also yield an upright pyramid. The phytoplankton makes up the base of the pyramid as the main producers in maximum numbers. These are followed by the herbivores such as small fish rotifers that serve as food for the secondary consumers. At the top of the pyramid of numbers, there are the bigger fish that are least in number.

However, not all pyramids of numbers need to be upright. A graphic representation of a parasitic food chain, on the other hand, will always be an inverted pyramid of numbers. The explanation for this is that one plant is capable of supporting the growth of several herbivores. In their turn, a few herbivores are able to offer nutrition to dozens of parasites that also provide for hundreds of hyperparasites.

Inverted biomass pyramid

Unlike pyramids of numbers, biomass pyramids are more fundamental. They emphasize the quantitative relationships and establish hierarchies based on the mass of the organisms. Upright biomass pyramids are mainly characteristic of forests and grasslands. However, ponds are usually characterized by inverted pyramids.

The reason behind this is that the producers at the base of the pyramid are small, which results in a low biomass. As the values of the biomass become larger approaching the apex, the pyramid gains an inverted shape, with tertiary consumers being the heaviest in biomass.

inverted Biomass Pyramid

Pyramid of energy

Both the pyramid of numbers and the biomass pyramid fail to accurately display the exchange of energy in the given ecosystem. Energy pyramids aim to present an accurate picture of the speed at which food is produced.

The pyramid of energy encompasses the rate in which the food mass goes through the food chain. This type of pyramid is always upright owed to the gradual energy decrease that takes place at successive trophic levels. Despite the fact that some organisms have small biomasses, their assimilated total energy that they pass on can be significantly larger than the energy of organisms boasting larger biomasses.

The distinct characteristic of the pyramid of energy is that, unlike the biomass pyramid, it pinpoints the role of individual organisms that play a part in the energy transfer. The graphs show the amount of energy required to support the following trophic level.

Image sources: 1, 2, 3, 4

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