Here we see a food pyramid that shows how the Kilocalories pass up the food chain. The first trophic level is occupied by the primary producers, which are the plants.
Plants make food through photosynthesis.
The limiting factor for these plants is the shortage of water, so they produce fewer than 200 Kilocalories of food for the animals for each square meter each year. The primary consumers , who eat the plants, occupy the second trophic level. These animals have very little to eat, and are small. Many are insects, or reptiles, who are cold blooded and who use less energy to maintain their bodies than mammals and birds do. As food for predators, they provide about 20 Kilocalories per square meter per year for predators.