According to the BBC, about 90 percent of the available energy in any trophic level is lost and becomes unavailable to higher trophic levels. For example, if the green plants in a habitat represent 1000 calories of food per square foot, the herbivores that eat these plants only represent about 100 calories per square foot. The predators that feed on these herbivores only represent about 10 calories per square foot.
In general, the more fertile the habitat, the more trophic levels it can support. Because energy is lost with each trophic level, the BBC explains that the number of possible trophic levels for any ecosystem is limited. Animals of the fourth trophic level only represent about one - one thousandth of the original energy, and by the time the fifth trophic level is reached, only about one - ten thousandth of the original energy remains in the food chain. Commercial farming operations try to minimize these inefficiencies to maximize profits.
Tropic levels lose energy due to several inefficiencies in the system. As noted by BioTopics.co.uk, some of these inefficiencies include the fact that plants and animals use energy during cellular respiration. Additionally, when animals eat food items, they rarely digest them completely, leading to wasted calories.