1) Ecosystems have trophic structures that determine energy flow and nutrient cycling through feeding relationships between species organized into trophic levels.
2) Producers, which include photosynthetic plants, algae, and bacteria, occupy the first trophic level and support all other levels by harnessing solar or chemical energy.
3) Consumers are organisms that feed on producers or other consumers and are ranked according to the trophic level they occupy, such as herbivores on the first level or carnivores on higher levels.