Question

Why is pyramid of number is always upright

Answer 1

The ecological pyramid is based on energy and biomass. The two are directly proportional such that larger organisms with more biomass, contain larger amounts of energy. They also require more resources and more oxygen (for cellular respiration) to sustain that energy. There is more energy available for organisms in tropical areas since they are closer to the equator and are thus, exposed to more sunlight.

The structure is a pyramid, an enclosed figure, because there is not enough energy to sustain infinite trophic levels. This is why predators such as lions do not have natural predators.

Moreover the distribution of energy and biomass is always reducing as the trophic level becomes higher (from primary producer to tertiary consumer). The structure also implicates the required amount of energy needed by each trophic level.As the pyramid go up, the energy flow decreases, that's why it's getting smaller and smaller.