Primary producers occupy the first trophic level.
Carnivores that eat herbivores occupy the third trophic level and are called secondary consumers. Although a few communities rely on chemosynthesis, the vast majority of energy fixed is fixed by photosynthesis. We will focus on photosynthesis. Temperature affects AET by affecting the rate at which water evaporates and transpires. Warm, wet biomes such as tropical rain forests have high primary productivity.