Which of the following could qualify as a top-down control on a grassland community?
a. Limitation of plant biomass by rainfall amount
b. Influence of temperature on competition among plants
c. Influence of soil nutrients on the abundance of grasses versus wildflowers
d. Effect of grazing intensity by bison on plant species diversity

Verified step by step guidance

1. Understand the concept of top-down control: In ecology, top-down control refers to the influence of predators or consumers on the structure and dynamics of ecosystems. It contrasts with bottom-up control, which is driven by resource availability such as nutrients or sunlight.
2. Analyze each option to determine if it represents a top-down control: Top-down control typically involves the impact of higher trophic levels (like predators or herbivores) on lower trophic levels (like plants).
3. Evaluate option a: Limitation of plant biomass by rainfall amount is a bottom-up control because it involves abiotic factors affecting plant growth.
4. Evaluate option b: Influence of temperature on competition among plants is also a bottom-up control, as it involves abiotic factors affecting plant interactions.
5. Evaluate option d: Effect of grazing intensity by bison on plant species diversity is a top-down control, as it involves herbivores (bison) affecting the diversity and composition of plant species in the grassland community.

Key Concepts

Top-Down Control

Top-down control refers to the influence of higher trophic levels on the structure and dynamics of ecosystems. In a grassland community, this could involve predators or herbivores affecting the abundance and diversity of plant species. For example, grazing by bison can regulate plant species diversity by selectively feeding on certain plants, thereby shaping the community composition.

Trophic Levels

Trophic levels are the hierarchical levels in an ecosystem, comprising producers, consumers, and decomposers. Each level represents a step in the food chain, with energy and nutrients flowing from one level to the next. Understanding trophic levels is crucial for identifying how top-down controls, such as herbivory, can impact lower levels like plant communities in grasslands.

Community Dynamics

Community dynamics involve the interactions and changes within an ecological community over time. Factors such as predation, competition, and environmental conditions can influence these dynamics. In the context of the question, grazing intensity by bison represents a biotic factor that can alter plant species diversity, demonstrating a top-down control mechanism in the grassland ecosystem.