Which of the following could qualify as a top-down control on a grassland community?

• A. Water availability during dry seasons
• B. Predation by hawks on small mammals
• C. Nutrient availability in the soil
• D. Competition among plant species for sunlight

Answer: (B)

Verified step by step guidance

1. Understand the concept of top-down control: In ecology, top-down control refers to the influence that predators (or higher trophic levels) exert on the structure and population dynamics of the ecosystem. This is in contrast to bottom-up control, which is driven by resource availability such as nutrients or sunlight.
2. Identify the options that represent top-down control: In the given options, look for factors that involve predation or influence from higher trophic levels.
3. Analyze each option: Water availability and nutrient availability are abiotic factors that influence the ecosystem from the bottom-up. Competition among plant species for sunlight is also a bottom-up factor as it involves resource competition.
4. Focus on predation: The option 'Predation by hawks on small mammals' involves a predator-prey relationship, where hawks (predators) control the population of small mammals (prey). This is a classic example of top-down control.
5. Conclude with the correct understanding: Based on the analysis, predation by hawks on small mammals is the only option that qualifies as a top-down control in the grassland community.