In which situation will gene swamping prevent local adaptation?

Gene swamping occurs when a high level of gene flow from a population with different traits overwhelms local adaptations, inhibiting the process of natural selection from allowing a population to adapt to its specific environment.

When gene flow is high and selection is weak, incoming alleles from a different population can easily incorporate into the local gene pool. This situation dilutes the impact of any existing local adaptations because the alleles being introduced may not be beneficial, or could even be maladaptive, in the local environment. Thus, the strong influx of genes prevents the local population from adapting to its specific conditions since advantageous traits are overshadowed by maladaptive traits coming from the neighboring population.

In contrast to this scenario, when selection is strong, local adaptations can be maintained despite some level of gene flow. If migration is low, it further allows the local population to respond to its specific environmental pressures without the interference of external alleles. High selection and migration would still favor local adaptations depending on the balance between the two factors, while both being low would generally allow populations to adapt more effectively as there would be minimal interference. Therefore, the assertion that high gene flow combined with weak selection can lead to gene swamping effectively captures why local adaptation can be undermined in this circumstance.