Charles Krebs and Colleagues Applied Three Different Treatments to Populations

Charles Krebs and colleagues applied three different treatments to populations to snowshoe hares: control (1) , add fertilizer to increase growth of food plants (3) , keep out mammalian predators by electric fences (2) , and keep out predators together with added fertilizer (11) . The numbers in parentheses represent the resultant numbers of hares relative to control numbers. What can you conclude?

A) Top-down control is most important
B) Bottom-up control is most important
C) Food limitation is important, but only after predator removal
D) Predation by hawks and owls is important