Answer:
He should use a food chain model.
Step-by-step explanation:
A food chain is defined as a linear sequence of the transfer of matter and energy in an ecosystem, in which it is possible to observe a sequence of organisms serving as food for others. For this reason, this would be an ideal model for someone who wants to show how energy moves in ecosystems. This transfer always starts with a producer and ends with a decomposer, this transfer being unidirectional.