Question

Which of the following examples can cause gene flow between populations?
an increase in predators to a population of zebra
a volcanic eruption that kills half of a population of mice
bird droppings that contain seeds from a different location
a person that sprays a toxin on a group of mosquitoes

Answer 1

Gene flow = movement of alleles between populations (via migration of individuals, gametes, seeds, etc.).

Of the examples, only the bird droppings with seeds from a different location cause gene flow. The others change allele frequencies by selection or drift (predator increase → selection; volcanic kill → bottleneck/genetic drift; toxin spray → selection), but do not introduce new alleles from another population.