Ecological pyramid

An ecological pyramid is a visual representation of the feeding relationships among living organisms in an ecosystem. Generally, large amounts of plants that feed themselves using the sun's energy occupy the wide "base" of the pyramid. The next level up is occupied by herbivores, or animals that eat plants. The topmost levels are occupied by carnivores, or animals that eat meat. This pyramid is meant to show how energy is transferred among living organisms. Some ecological pyramids may record the populations of living organisms, their combined mass, or the amount of energy they contain. Ecological pyramids may be used to graph the inhabitants of any ecosystem on land or in water and may not always conform to a true triangular shape. Zoologist Charles Elton created the first ecological pyramid in 1927.

Background

In the late nineteenth and early twentieth centuries, scientists took an increased interest in the workings of nature. Rather than just trying to determine how humans could benefit from natural resources, scientists sought new insights into the relationships among organisms and between organisms and their physical surroundings. This pursuit of knowledge contributed to the field of ecology.

One of the important figures in early ecology was English zoologist Charles Elton. In 1927, he devised the theory of the ecological pyramid, sometimes known as the "Elton pyramid" in his honor. This graph demonstrated how organisms gain or lose energy due to their feeding habits. American ecologist Raymond Lindeman later expanded on this theory. In 1942, Lindeman elaborated on the rates at which energy was produced and consumed in a natural system.

Elton's theory was important in that it showed that the transfer and loss of energy in a food chain can be measured and graphed. Moreover, the results of the measurements would almost certainly conform to a predictable pattern. This pattern usually took the form of a triangle or a pyramid in which the largest energy source was on the wide bottom and the smallest was on the narrow top.

Generally, the largest energy source consists of plants that produce their own food from the energy of sunlight. Plant-eating animals called herbivores then eat these plants, thus ingesting much of their energy. After that, meat-eating animals called carnivores eat the herbivores and take in their energy. In the end, the death and decay of carnivorous animals helps to nourish the plant level and restart the system.

Although the system appears to be an efficient transfer of energy, it involves a significant energy loss at each stage. Only a small amount of the original energy stored in the plants reaches the final carnivore. Ecologists and other scientists have used this information to draw important conclusions about energy use, conservation, and the importance of balanced ecosystems.

Overview

The ecological pyramid is meant to create a visual representation of the feeding relationships among living organisms in an ecosystem. The organisms are divided into groups known as trophic levels; the word trophic relates to feeding. Three main trophic categories make up an ecological pyramid.

Generally, the first and largest trophic group is made of photosynthetic autotrophs. This is a large category of organisms that create their own food through the process of photosynthesis. Photosynthesis is the process by which green plants and some other organisms create food from the energy of sunlight. This group is generally very large and forms the wide base of the ecological pyramid. Depending on the ecosystem, this level may be occupied by grass, trees, phytoplankton, or any other plant life.

The next level of the ecological pyramid is usually composed of herbivorous heterotrophs, which are organisms that eat plants. Depending on the ecosystem, these organisms may be large or small, and they will likely eat a large amount of plant food to take in their needed energy. This level will be somewhat smaller than the previous level. Depending on the ecosystem, it may be occupied by insects, grazing animals, or other plant-eating creatures.

The next and highest level of the ecological pyramid is occupied by carnivorous heterotrophs, which are living organisms that eat meat. These creatures prey mainly on plant-eating organisms. Multiple levels of carnivores may exist in this level, with the most powerful creature, known as the apex predator, on top. The uppermost level of an ecological pyramid, forming the "tip," will almost certainly be the smallest level. Carnivorous animals include many fish, birds, and a wide variety of other animals. Apex predators are the most powerful, such as lions, sharks, or humans.

At each stage of the energy transfer, a significant amount of energy is lost as heat. The amount of energy available limits the number of organisms that can live in an ecosystem, and the reduction of energy causes the decreasing number of organisms in the upper levels of the ecological pyramid. Even the top levels surrender some of their energy during the process of decay after death.

Three varieties of ecological pyramids are number, biomass, and energy. The most basic is the number pyramid. This records the population of living things at each trophic level. For example, the population may include one thousand plants, one hundred herbivores, and ten carnivores in an ecosystem. This kind of pyramid does not consider any of the other important information about the organisms or the energy they transfer.

The biomass pyramid presents the combined weight of organisms in each trophic level. While this measure may give an idea of scale and ratio, it may not provide the most useful data, since some large living things (such as trees) may provide a proportionately small amount of nourishment to other creatures, whereas some small living things (such as phytoplankton) may provide a large proportion of nourishment.

The energy pyramid may be the most accurate, as it shows the total amount of energy, as measured in calories or joules, existing in each trophic level. This type of pyramid most clearly shows the ratio at which energy is transferred and lost during the feeding cycle.

Ecological pyramids normally conform to a triangular shape with the widest part on the bottom. Some ecosystems and some methods of measurement, however, may yield different shapes. In these cases, the "pyramid" may be spindle-shaped or even inverted while still containing valid and accurate data.

Bibliography

Bhatnagar, M. C., and Geeta Bansal. Ecology and Wildlife Biology. Krishna Prakashan Media, 2010. 

Chauhan, B. S. Environmental Studies. University Science Press, 2008.

Corwin, Anabell. "Ecological Pyramids." Gould Academy, https://gouldacademy.instructure.com/courses/400318/pages/ecological-pyramids. Accessed 25 Nov. 2024.

Hanks, Sharon La Bonde. Ecology and the Biosphere: Principles and Problems. St. Lucie Press, 1996.

Kumar, Arvind. A Textbook of Environmental Science. S.B. Nangia/APH Publishing, 2008.

Mongillo, John, and Linda Zierdt-Warshaw. Encyclopedia of Environmental Science. Oryx Press, 2000.

"Trophic Pyramid." Encyclopedia Britannica, 10 Oct. 2024, https://www.britannica.com/science/trophic-pyramid. Accessed 25 Nov. 2024.