A study exаmines hоw prey аvаilability affects cheetah pоpulatiоn size in two hypothetical wildlife reserves. The Savanna Plains Reserve maintains its natural prey levels and serves as the baseline population, while the Kijani Wildlife Reserve experiences an increase in prey through managed translocation. Over several years, researchers monitor changes in the cheetah populations in both reserves using GPS collars and population surveys. Differences in cheetah population size between Savanna Plains Reserve and Kijani Wildlife Reserve are used to evaluate the ecological impact of prey availability. Which of the following is the control?