Step 1: Understand what ecosystem ecology covers.
Ecosystem ecology focuses on the interactions between living (biotic) and non-living (abiotic) components such as energy flow, nutrient cycling, and matter transfer.
Step 2: Eliminate incorrect options.
(A) Organism behavior relates to behavioral ecology, not ecosystem ecology.
(B) Interaction among individuals in a population is studied in population ecology.
(D) Community ecology studies interactions among different species.
Step 3: Conclusion.
Thus, ecosystem ecology emphasizes biotic–abiotic interactions, making option (C) correct.