Question

how might gene flow between two duck populations impede each populations ability to be adapted to its local environment?
gene flow would keep the ducks from breeding with each other.
the new alleles would prevent random mating, so no new combinations would arise.
the new alleles would not introduce any new traits, so the ducks couldnt evolve.
introduced alleles may produce traits that cause more harm than good to the resident population.

Explanation:

Gene flow introduces new alleles. These alleles may produce traits that are not well - suited to the local environment of a population. For example, if one duck population is adapted to a cold climate (with certain allele combinations for thick feathers) and another from a warmer climate (with alleles for thinner feathers) has gene flow between them. The new alleles (e.g., for thinner feathers in the cold - adapted population) can disrupt the local adaptation.

Answer:

The introduced alleles may produce traits that cause more harm than good to the resident population.