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.

1) gene flow

- it is described as the transfer of genes from one population to another population so that frequency of gene is increased.

-a zebra migrates to join a different herd of zebras.

2) natural selection

- a mechanism of evolutionary change in which individuals with advantageous traits survive and reproduce whereas the others ( those that can not adapt) eliminate from the population.

-competition for sunlight leads to taller trees.

3) mutation

- permanent change in the nucleotide sequence of dna ( genetic material) that could have harmful or useful consequences.

-the dna of a snake changes to make its venom stronger.

4) genetic drift - it is a random phenomenon ( that occurs by chance such as fire) that results in change in the gene frequency in a small population.    

-a grassfire randomly sweeps through a population of buffalo and kills most of the animals.

explanation:

it would affect precipitation by causing flooding in some areas of the world due to climate increasing, causing the glaciers in the northern and southern pole of our planet to melt.

i wish you would have provided choices to simplify it and allow me to give an exact answer.