Primary consumers in an ecosystem are primarily herbivores that feed on producers, such as plants and algae. They play a crucial role in the food web by transferring energy from producers to higher trophic levels, like secondary consumers. Primary consumers help control plant populations and contribute to nutrient cycling within ecosystems. Their feeding habits can influence vegetation structure and overall ecosystem health. Examples of primary consumers include deer, rabbits, and numerous insects. Their presence is essential for maintaining the balance of energy flow within an ecosystem.