What is meant by bottom-up controls in ecology?

Bottom-up controls in ecology refer to the influences exerted by physical and chemical factors, such as nutrient availability, sunlight, and water, on the primary production within an ecosystem. These factors are crucial because they determine the abundance and productivity of primary producers, primarily plants and phytoplankton, which form the foundation of food webs.

When these resources are abundant, primary producers can thrive, leading to greater biomass and subsequent increases in herbivore and predator populations due to the enhanced availability of food. Conversely, when these physical and chemical conditions are limiting, primary production decreases, which can cascade up the food chain and affect higher trophic levels.

Understanding bottom-up controls is essential for studying ecosystem dynamics, as it emphasizes how the base of the food web directly influences the entire ecosystem's structure and function.