Exam 3: Evolutionary Change and Adaptation

A gardener is constantly struggling with the growth of weeds in his perennial flower beds. At the start of the growing season one year, he sprays an herbicide to reduce the number of weeds. Although the herbicide kills many of the weeds, some develop resistance to the herbicide and continue to grow and spread among his flowering plants. After a few years, the gardener decides to stop all herbicide applications. One of the changes that he notices is that the weeds that have resistance to herbicides grow much more slowly and are easily outcompeted by other weeds when no pesticides are sprayed (i.e., the herbicide-susceptible weeds produce more seeds and quickly overtake some of the areas in the garden where the herbicide-resistant weeds had been growing). Resistance to herbicides has arisen in the population through the process of __________.

A gardener is constantly struggling with the growth of weeds in his perennial flower beds. At the start of the growing season one year, he sprays an herbicide to reduce the number of weeds. Although the herbicide kills many of the weeds, some develop resistance to the herbicide and continue to grow and spread among his flowering plants. After a few years, the gardener decides to stop all herbicide applications. One of the changes that he notices is that the weeds that have resistance to herbicides grow much more slowly and are easily outcompeted by other weeds when no pesticides are sprayed (i.e., the herbicide-susceptible weeds produce more seeds and quickly overtake some of the areas in the garden where the herbicide-resistant weeds had been growing). Assuming the gardener continues to spray the herbicide for five years, do you think the weed population will evolve?

The graph below represents the results of an experiment looking at mate preference in female black widowbirds. The researcher used three groups of male birds: one with artificially shortened tails, one with artificially lengthened tails, and the control group with unaltered tail lengths. What type of selection is likely demonstrated in this experiment?