Energy is decreasing by 500 because some of it is turned into heat energy.
Step-by-step explanation:
when an animal/creature consumes another living thing and or something that has energy it is decrease to a certain amount because some of the energy that the original animal/creature had is turned into heat energy because they use some of the energy for themselves to survive and live.
For example:
A flower is a producer because it produces energy and gets it gets eaten by a deer and some energy gets changed to heat and the other is consumed by the consumer (the deer) and so on.