Community Level Systems: Pyramids of Biomass and Number
Community Level Systems: Pyramids of Biomass and Number
Pyramids of Biomass
- In ecological studies, a pyramid of biomass illustrates the relative amount of biomass (or mass of organisms) at each trophic level.
- The base of the pyramid represents producers, generally plants, which have the greatest biomass. Each successive level represents the consumers that eat the organisms from the level below it, and so have less biomass.
- The pyramid shape results from energy being lost at each trophic level through waste products and heat during metabolic processes like cell respiration.
- A pyramid of biomass does not always have a pyramid shape if it involves unusual organisms or environments. For instance, the biomass of zooplankton (tiny floating animals) can exceed the biomass of phytoplankton (tiny floating plants) they consume in parts of the ocean.
Pyramids of Number
- A pyramid of numbers shows the relative numbers of individuals at each trophic level.
- Unlike a pyramid of biomass, the shape of a pyramid of numbers can vary greatly. It is not always a typical pyramid shape – for instance, where one tree (producer) may support many herbivores (consumers).
- The pyramid, however, always starts with the producers at the bottom and levels off with top predators. The shape depends on the numbers of organisms at each trophic level.
Comparison of Biomass and Number Pyramids
- Pyramids of biomass and pyramids of numbers may not always look the same for a given community.
- Discrepancies can arise especially when larger organisms, such as trees, are outnumbered by smaller organisms like insects. In such situations, a pyramid of number will be inverted (with the broad end representing insects and the pointed end representing trees) while the pyramid of biomass will still be upright (because the total biomass of trees is more than that of insects).
- Both types of pyramids are useful for different types of ecological analysis, and using them in combination can give a well-rounded understanding of the community under study.
Community Interactions
- When interpreting pyramids of biomass or number, it’s important to consider the interactions between different species in the community.
- Predator-prey relationships, competition between species, disease, and environmental factors can all dramatically shape these pyramids over time.
- Understanding the principles behind pyramids of biomass and number can help reveal the complex dynamics at work in nature’s diverse ecosystems.