Energy flows in ecosystems

All organisms in an ecosystem can be placed on a trophic level, depending on whether they are producers or consumers of energy within the food chain (see the photo). Ecologists have long debated what regulates the trophic structure and dynamics of ecosystems (1). This is important because trophic structure and dynamics regulate many of the goods and services that ecosystems provide to wildlife and humankind, such as the production of harvestable food and energy, carbon sequestration and modulation of climate change, and nutrient uptake and control of global biogeochemical cycles (2). A study by Hatton et al. on page 1070 of this issue (3) and a recent report by Lafferty et al. (4) represent important advances toward a unified theory of trophic structure that captures observed trends across all ecosystems.