Ecological Tolerance Practice Test

A tolerance curve for a freshwater trout shows survival versus water temperature. Survival is maximal at 12–16°C, reduced at 6–12°C and 16–20°C, and zero below 6°C or above 20°C. Which temperature best represents the upper limit of tolerance?

A tolerance curve for a cactus shows growth versus nighttime temperature. Growth is maximal at 15–20°C, reduced at 5–15°C and 20–30°C, and zero below 5°C or above 30°C. Which nighttime temperature would most likely cause the cactus to experience stress but still grow?