A wildlife biologist has adopted a number of techniques to protect the Willow Flycatcher, a bird that often nests and feeds in willows. Some techniques reflect top-down while some reflect bottom-up control. Which of the following approaches demonstrates her understanding of how top-down forces affect community dynamics?

a. Both approaches rely on bottom-up forces.
b. Willow Flycatchers can lose eggs to squirrels, weasels, and other predators. The biologist attempts to protect nests by putting metal collars around the base of the willows that keep ground predators from climbing up to reach the nests.
c. The biologist attempts to increase food availability by reintroducing beaver. She hypothesizes that beaver will raise the water table, stimulating the growth of willow, which will result in an increase in insect abundance, giving flycatchers more food.
d. Both approaches rely on top-down forces.