In the trophic relationship between producers and different types of con­sumers, the number and mass of the organisms at each step is limited by the amount of energy available since same amount of energy is always lost at every step of the reaction as per the laws of thermodynamics. Progres­sively at each step the bio mass (number of organisms) becomes smaller as it reaches the top (i.e. reaches the level of carnivores). This relationship which can be graphically represented with a wise base and a narrow top is called as ecological pryramid.