Final answer:
Monogamous relationships provide evolutionary advantages such as mate-guarding in scarce environments, increased offspring survival through male parental care, and exclusive investment in one's offspring through female enforcement.
Step-by-step explanation:
An advantage of a monogamous relationship is that it ensures that each male has a mating partner when very few males are available in a population. An advantage of a monogamous relationship includes the benefit of mate-guarding, where males stay with the female to prevent other males from mating with her. This is particularly advantageous in environments where mates are scarce.
Additionally, monogamy is supported by the male-assistance hypothesis, suggesting that males that help in rearing young will have more and healthier offspring. In many bird populations, males provide significant parental care, which supports the survival and health of their chicks. Lastly, the female-enforcement hypothesis highlights the female's role in ensuring that the male's resources are exclusively invested in her offspring, thus preventing the male from having other offspring that could compete for resources.