What phenomenon explains the decrease in population size as you move up the food chain?

The decrease in population size as you move up the food chain can be attributed to the phenomenon of insufficient energy to support larger organisms. This concept is commonly illustrated by the energy pyramid, which demonstrates that energy transfer between trophic levels is inefficient.

Only a small fraction of energy is passed on from one trophic level to the next—typically around 10%—with the remainder of the energy lost primarily through metabolic processes as heat, consumption, and waste. Consequently, as energy flows from primary producers (like plants) to primary consumers (herbivores), and then to secondary consumers (carnivores), there is less energy available to sustain populations at higher trophic levels.

Therefore, while lower levels of the food chain can support large populations of producers and consumers, the number of individuals that can be supported diminishes significantly as one moves up to higher trophic levels. This results in smaller population sizes for top predators compared to those lower in the food chain.