Herbivores play a crucial role in an ecosystem by acting as primary consumers, feeding on producers like plants and algae. This grazing helps to control plant populations and maintain biodiversity. Herbivores facilitate nutrient cycling through their waste, which adds organic matter to the soil, improving its fertility. Additionally, they serve as a food source for carnivores and omnivores, thus supporting the entire food web. The presence of herbivores can also influence plant community structures, promoting the growth of diverse species.