Most of the energy that flows through a forest ecosystem flows through detritus-based food chains, and the detritus consists mainly of dead plant tissues (e.g., leaves and wood). In contrast, most of the energy flowing through a pelagic marine or freshwater ecosystem flows through grazing food chains with phytoplankton constituting the major primary producers. Ecologists have determined that on average, a calorie or joule of energy takes only several days to pass through the pelagic ecosystem but a quarter of a century to pass through the forest ecosystem. Explain.