What is the independent variable in the study examining cane toads' effect on black snakes?

• A. Time since first exposure to cane toads.
• B. Predation rate on cane toads by black snakes.
• C. The size of the study area.
• D. The ambient temperature.

Answer: (A)

In experiments, the independent variable is the factor the researchers deliberately vary to see its effect. Here, scientists are looking at how black snakes respond to cane toads as time passes after the first exposure. So the element being changed or tracked across conditions is the time since first exposure to cane toads. The response they measure—such as the predation rate on cane toads by black snakes or other behavioral outcomes—is the dependent variable. The size of the study area and ambient temperature are environmental factors that could influence results, but they are not the main factor being manipulated to test cause-and-effect in this question.