Final answer:
Male lions alter allele frequencies in lion populations through gene flow when they move between and join new prides, bringing new genetic combinations that lead to variation within the population.
Step-by-step explanation:
When male lions reach sexual maturity and leave their pride to join a new one, they alter the allele frequencies of the lion population through gene flow. This process stems from the immigration and emigration of individuals, in this case, male lions moving between prides, which brings new genetic combinations into a pride's gene pool. It contributes to the introduction of new genetic variation to populations in different geographical locations and can subsequently affect aspects of lion diversity such as size, strength, or mane color.
It is distinct from genetic drift, which is the change in allele frequencies due to chance events. Genetic drift may also play a role when male lions that happen to find a new pride successfully mate, depending on how many offspring they produce. Nevertheless, the primary mechanism at work when lions change prides and mate is gene flow, as it involves the physical movement of genes between populations.