Which of these Eltonian pyramids are correctly described ?

Options

A. Pyramid of numbers - may be erect or inverted , Pyramid of biomass - may be erect or inverted , Pyramid of energy - may be erect or inverted , Pyramid of energy - may be erect or inverted
B. Pyramid of numbers - always erect, pyramid of biomass - may be erect or inverted , pyramid of energy - may be erect or inverted
C. Pyramid of numbers - may be erect or inverted , Pyramid of biomass - may be erect, Pyramid of energy - may be erect or inverted
D. Pyramid of numbers - may be erect or inverted , Pyramid of biomass - may be erect, Pyramid of energy - always erect

Answer

To determine which of the Eltonian pyramids are correctly described, we need to analyze the characteristics of the three types of pyramids: pyramid of numbers, pyramid of biomass, and pyramid of energy.

### Step-by-Step Solution:

1. **Pyramid of Numbers**:
- This pyramid represents the number of individual organisms at each trophic level.
- It can be either erect or inverted depending on the ecosystem. For example, in a forest, there may be many insects (producers) compared to a few birds (primary consumers), leading to an inverted pyramid.
- **Conclusion**: The statement "Pyramid of numbers may be erect or inverted" is **correct**.

2. **Pyramid of Biomass**:
- This pyramid represents the total biomass (mass of living organisms) at each trophic level.
- Similar to the pyramid of numbers, the pyramid of biomass can also be erect or inverted. In some aquatic ecosystems, for instance, the biomass of primary producers (like phytoplankton) can be less than that of primary consumers (like zooplankton).
- **Conclusion**: The statement "Pyramid of biomass may be erect or inverted" is **correct**.

3. **Pyramid of Energy**:
- This pyramid represents the flow of energy through each trophic level.
- The pyramid of energy is always erect because energy decreases as it moves up the trophic levels (due to energy loss at each level). It cannot be inverted.
- **Conclusion**: The statement "Pyramid of energy may be erect or inverted" is **incorrect**. It is always erect.

### Summary of Each Option:
- **Option 1**: Pyramid of numbers may be erect or inverted (correct), pyramid of biomass may be erect or inverted (correct), pyramid of energy may be erect or inverted (incorrect).
- **Option 2**: Pyramid of numbers always erect (incorrect), pyramid of biomass may be erect or inverted (correct), pyramid of energy may be erect or inverted (incorrect).
- **Option 3**: Pyramid of numbers may be erect or inverted (correct), pyramid of biomass may be erect or inverted (correct), pyramid of energy may be erect or inverted (incorrect).
- **Option 4**: Pyramid of numbers may be erect or inverted (correct), pyramid of biomass may be erect (correct), pyramid of energy always erect (correct).

### Final Answer:
The only option that correctly describes the Eltonian pyramids is **Option 4**.