Question

multiple choice question
unlike top-down control, bottom-up control ______.

influences population densities

is influenced by abiotic factors

is based on food limitations

Explanation:

1. Analyze each option:

• Option 1: Both top - down and bottom - up control can influence population densities. So this is not a distinguishing factor.
• Option 2: Bottom - up control is mainly driven by abiotic factors (like nutrient availability, climate) that affect the lower trophic levels and then cascade up. Top - down control is more about biotic factors (like predation) from higher trophic levels. So bottom - up control is influenced by abiotic factors, which is a key difference from top - down.
• Option 3: Food limitations are more related to top - down control (e.g., predators limiting prey which affects food availability for the prey) or can be part of both, but it's not the main distinction for bottom - up vs top - down. Bottom - up is more about the base of the food web (producers) being limited by abiotic factors.

Answer:

B. is influenced by abiotic factors