Question

Which type of ecological pyramid is always upright?

• A. Pyramid of number
• B. Pyramid of biomass
• C. Pyramid of energy
• D. Pyramid of individuals

Answer 1

Answer:

C. Pyramid of energy

Understanding Ecological Pyramids

• Ecological pyramids are graphical representations showing the relationship between different trophic levels in an ecosystem. They illustrate the biomass, numbers, or energy content at each successive trophic level.
• There are three main types of ecological pyramids: Pyramid of Energy, Pyramid of Biomass, and Pyramid of Numbers.

Pyramid of Energy: Always Upright

• The Pyramid of Energy is the only ecological pyramid that is always upright and can never be inverted.
• It depicts the total amount of energy at each trophic level in a food chain. Energy flow in an ecosystem is always unidirectional, from producers to consumers.
• This upright shape is due to the 10% Law of Energy Transfer (also known as Lindeman's Law), which states that only about 10% of the energy from one trophic level is transferred to the next trophic level. The remaining 90% is lost, primarily as heat during metabolic activities (respiration).
• Therefore, the energy content continuously decreases at successive trophic levels, resulting in a broad base (producers) and a progressively narrower top (top consumers).

Pyramids that can be Inverted

• Pyramid of Biomass: This pyramid represents the total biomass (living organic matter) at each trophic level. While it is typically upright in most terrestrial ecosystems (e.g., grassland ecosystem), it can be inverted in certain aquatic ecosystems. For instance, in an aquatic ecosystem, the biomass of producers (phytoplankton) might be less than the biomass of primary consumers (zooplankton) that feed on them, because phytoplankton have a very short lifespan and high reproductive rate, so a small standing crop can support a larger zooplankton biomass.
• Pyramid of Numbers: This pyramid illustrates the number of individual organisms at each trophic level. It can be upright (e.g., grassland ecosystem where grass is abundant), inverted, or spindle-shaped. An example of an inverted pyramid of numbers is a forest ecosystem where a single large producer (a tree) supports numerous primary consumers (e.g., birds, insects), which in turn support even more secondary consumers (e.g., parasites on birds). A spindle-shaped pyramid can occur where producers are fewer than primary consumers, but secondary consumers are fewer than primary consumers.

Key Takeaways for Competitive Exams

• Energy flow is unidirectional and always decreases at higher trophic levels.
• The 10% Law of Energy Transfer is a fundamental concept in ecology, explaining energy loss and pyramid structure.
• Producers form the base of all ecological pyramids as they are the primary source of energy.
• Understanding which pyramids can be inverted and why (e.g., aquatic biomass, forest numbers) is crucial.