Question

a population of birds lives on a small island. another population of the same species lives on the mainland. the distance between the island and the mainland is too great for birds to fly back and forth. recently, a series of sandbars and tiny islands have formed between the island and the mainland.

what is the most likely effect of this?

an increase in mutations in both bird populations
an increase in gene flow between the bird populations
an increase in genetic drift between the bird populations
an increase in mutations in the island population

Explanation:

1. Analyze the effect of sandbars/tiny islands: The sandbars and tiny islands form a "bridge" that reduces the isolation between the island and mainland bird populations.
2. Evaluate Option 1 (mutations): Mutations are random and not directly caused by reduced isolation, so this is incorrect.
3. Evaluate Option 2 (gene flow): Gene flow is the transfer of genetic material between populations. With the new landforms, birds may now be able to move between the two areas, increasing gene flow. This matches the scenario.
4. Evaluate Option 3 (genetic drift): Genetic drift is random change in allele frequencies, often in small populations. The new landforms don't directly increase genetic drift between the populations.
5. Evaluate Option 4 (mutations in island population): Mutations are not triggered by the formation of landforms connecting populations, so this is incorrect.

Answer:

B. an increase in gene flow between the bird populations