How does the loss of biomass at each trophic level affect the number of organisms in a food chain or ecosystem?

SouravNovember 12, 2024

Answered step-by-step

The loss of biomass at each trophic level significantly affects the number of organisms in a food chain or ecosystem. Here’s how this process works and the implications for biodiversity and ecosystem dynamics:

1. Energy Transfer Efficiency

• 10% Rule: On average, only about 10% of the energy (and thus biomass) from one trophic level is transferred to the next. This means that as energy moves up the food chain, there is a substantial loss at each level due to metabolic processes, waste production, and heat loss during respiration. The remaining 90% is not available for the next trophic level, limiting the amount of biomass that can be supported higher up in the food chain.

2. Decreased Biomass at Higher Trophic Levels

• Fewer Organisms: Because of the inefficiency in energy transfer, there are typically fewer organisms at higher trophic levels compared to those at lower levels. For example, in a grassland ecosystem, there may be a large biomass of grasses (producers), fewer herbivores (primary consumers), and even fewer carnivores (secondary and tertiary consumers). This pattern results in a pyramid shape when visualized in a pyramid of biomass.

3. Limited Number of Trophic Levels

• Trophic Level Limits: The significant energy loss between trophic levels restricts the number of levels that can be supported in an ecosystem. Generally, ecosystems can sustain only three to six trophic levels because after this point, there is insufficient energy to support additional levels. For instance, if a primary producer has 10,000 kilocalories of energy, only about 1,000 kilocalories will be available to primary consumers, and even less (about 100 kilocalories) will reach tertiary consumers .

4. Implications for Biodiversity

• Reduced Species Diversity: As biomass decreases at higher trophic levels, the number of species that can exist within these levels also diminishes. This reduction can lead to decreased biodiversity overall since fewer species can occupy higher trophic levels. For example, if top predators are lost due to insufficient prey availability (due to low biomass), it can disrupt ecological balance and lead to overpopulation of herbivores .
• Ecosystem Stability: A decrease in biodiversity can negatively impact ecosystem stability and resilience. Diverse ecosystems are generally more resilient to environmental changes and disturbances. When species diversity is low, ecosystems become more vulnerable to diseases, invasive species, and climate change impacts .

5. Ecological Pyramids

• Representation of Biomass Loss: The pyramid of biomass visually represents how biomass decreases from producers at the base to top predators at the apex. This representation illustrates not only the number of organisms but also their sizes—typically larger organisms at higher trophic levels but in smaller numbers due to lower available energy