Examine the scenarios on the following pages. For each scenario:

a. Decide whether or not natural selection is operating. In doing this, indicate whether there is variability in the population(s).

If no, what does this imply about evolution?

If yes, what is the nature of the variation? For example, what characteristics must the variation have for selection to operate on it?

b. Is there any indication that members of the population(s) differ in fitness?

If no, what does this imply about the operation of natural selection?

If yes, describe the difference in fitness.

c. Given your answers to parts a and b, what trend should characterize the future behavior or composition of the population(s)?

Scenario 1: A particular species of mouse feeds on the seeds of a single species of cherry tree. When the mice eat a seed, they digest it completely. The mice choose seeds of intermediate and large sizes, leaving the very small seeds of the cherry tree uneaten

Scenario 2: Small island A contains three separate populations of a single species of cherry tree. The seed size varies between trees. That is, some trees produce seeds that are all in the small size ranges, others produce seeds all in the middle size ranges, and others produce seeds in the large size ranges. A small population of mice is introduced to the island. The mice eat cherries and are the only predators on the cherry trees. When the mice eat a cherry, they completely digest it and the pit or seed inside it. The mice choose medium and large seeds and leave the smallest seeds uneaten

Scenario 3: Would your answer for Scenario II change given the following information? Explain.

As you continue to study the populations of trees, you note that the viability of the seeds varies with size such that the viability of the small seeds is less than that of the middle-sized seeds, which is less than that of the largest seeds

Scenario 4: After a severe spring ice storm, about half of the finches (small birds) in a population are found dead. Examination of the dead birds indicates that they vary in age from young to old. About 60% of the dead are fledglings (just left the nest); about 20% are over 3 years of age (old for this species) (6 points).