How does female-defense polygyny occur when females live in groups?

In zoology, female-defense polygyny occurs when the spatial distribution of females allows a dominant male to monopolize access to them directly.12

When females live in groups, they are often clumped together due to the distribution of essential resources, such as food and nesting sites, or because of the survival benefits gained from forming social alliances. This clumping makes the females "economically defendable" as a group. Consequently, a dominant male can defend the entire cluster of females from rival males, thereby securing multiple mating opportunities.12

This mating system is frequently observed in species where group living is an adaptation to environmental pressures, such as the need to graze in open areas where individuals are highly visible to predators. In such contexts, the aggregation of females creates the specific opportunity for a single male to exert control over the group's reproductive access. This often leads to sexual dimorphism, where males are significantly larger than females, as increased body size provides a competitive advantage in the physical defense of the female group against other males.21