Which of the following plays a critical role in the ecosystem by cycling nutrients?

Nutrient cycling is a fundamental process in ecosystems that ensures the availability of essential elements for organisms. Predators play a critical role in this cycle by influencing the population dynamics of prey species, which in turn affects the energy flow and nutrient distribution within an ecosystem.

When predators consume prey, they help control prey populations, preventing overgrazing and promoting a balance in species diversity. This balance allows for various plant and microbial communities to thrive, which are integral to nutrient cycling. The organic matter from predator waste contributes to soil quality and nutrient availability when decomposed.

Additionally, predators often determine the health of prey populations, which can influence the abundance of primary producers in an ecosystem. Healthy prey populations contribute to the cycling of nutrients as they feed on plants, returning nutrients to the soil upon their death or through their metabolic waste.

While prey has an essential role in supporting the food web, and precipitation is crucial for the water cycle, neither encompasses the whole process of nutrient cycling as thoroughly as the role of predators. Riffles, which are shallow areas in rivers where water flows rapidly and oxygen is mixed into the water, contribute to aquatic ecosystems but do not directly cycle nutrients as predators do.