46.2D: Ecological Pyramids
- Explain the shape and structure of the ecological pyramid
Modeling ecosystems energy flow: ecological pyramids
The structure of ecosystems can be visualized with ecological pyramids, which were first described by the pioneering studies of Charles Elton in the 1920s. Ecological pyramids show the relative amounts of various parameters (such as number of organisms, energy, and biomass) across trophic levels. Ecological pyramids can also be called trophic pyramids or energy pyramids.
Pyramids of numbers can be either upright or inverted, depending on the ecosystem. A typical grassland during the summer has an upright shape since it has a base of many plants, with the numbers of organisms decreasing at each trophic level. However, during the summer in a temperate forest, the base of the pyramid consists of few trees compared with the number of primary consumers, mostly insects. Because trees are large, they have great photosynthetic capability and dominate other plants in this ecosystem to obtain sunlight. Even in smaller numbers, primary producers in forests are still capable of supporting other trophic levels.
Another way to visualize ecosystem structure is with pyramids of biomass. This pyramid measures the amount of energy converted into living tissue at the different trophic levels. Using the Silver Springs ecosystem example, this data exhibits an upright biomass pyramid, whereas the pyramid from the English Channel example is inverted. The plants (primary producers) of the Silver Springs ecosystem make up a large percentage of the biomass found there. However, the phytoplankton in the English Channel example make up less biomass than the primary consumers, the zooplankton. As with inverted pyramids of numbers, the inverted biomass pyramid is not due to a lack of productivity from the primary producers, but results from the high turnover rate of the phytoplankton. The phytoplankton are consumed rapidly by the primary consumers, which minimizes their biomass at any particular point in time. However, since phytoplankton reproduce quickly, they are able to support the rest of the ecosystem.
Pyramid ecosystem modeling can also be used to show energy flow through the trophic levels. Pyramids of energy are always upright, since energy is lost at each trophic level; an ecosystem without sufficient primary productivity cannot be supported. All types of ecological pyramids are useful for characterizing ecosystem structure. However, in the study of energy flow through the ecosystem, pyramids of energy are the most consistent and representative models of ecosystem structure.
Key Points
- Pyramids of numbers can be either upright or inverted, depending on the ecosystem.
- Pyramids of biomass measure the amount of energy converted into living tissue at the different trophic levels.
- The English Channel ecosystem exhibits an inverted biomass pyramid since the primary producers make up less biomass than the primary consumers.
- Pyramid ecosystem modeling can also be used to show energy flow through the trophic levels; pyramids of energy are always upright since energy decreases at each trophic level.
- All types of ecological pyramids are useful for characterizing ecosystem structure; however, in the study of energy flow through the ecosystem, pyramids of energy are the most consistent and representative models of ecosystem structure.
Key Terms
- ecological pyramid : diagram that shows the relative amounts of energy or matter or numbers of organisms within each trophic level in a food chain or food web