The energy transfer through the food chain is not 100% from one consumer to another, or from the producer to the primary consumer, but instead it is around 10%. This means that if a producer has the 100% of energy, as it is the one that produces it, the primary consumer will only get 10% of its energy while consuming it, while the predator of the the primary consumer will only 10% from the primary consumer, or rather only 1% from the energy of the producer. In this case we have 200 kg of plant material. The plant material represents a producer, thus it is the one with 100% of energy. A herbivore will eat the plant material, getting 10% of its energy, thus this plant material is supporting about 20 kg of herbivore. The predator of the herbivore gets only 10% from the herbivore's energy, or only 1% of the producer's energy, thus only 2 kg of predator can be supported by the initial plant material.
