Final answer:
In the species where males compete for territory and access to females, the type of sexual selection at work is intrasexual selection, which is male-male competition that leads to sexual dimorphism and traits that increase males' reproductive success.
Step-by-step explanation:
The type of sexual selection acting in the species mentioned, where males are significantly larger than females and compete with one another for territory and access to females, is known as intrasexual selection. This form of sexual selection involves male-male competition, such as fighting for territory and the right to mate with females. In contrast, intersexual selection occurs when one sex, typically females, selects mates based on certain desirable traits such as colors, behaviors, or structures built by males to impress potential mates.
Sexual dimorphism, which can be observed in these mammal species, refers to the variance between males and females in size and other traits due to sexual selection. The differences arise because males with certain characteristics, such as larger size or more elaborate ornaments, tend to have greater reproductive success, either by winning fights against other males or by being chosen by females for mating.
In summary, sexual dimorphism and sexual selection directly affect the reproductive success of individuals within a species. Intrasexual selection is a type of sexual selection characterized by competition within the same sex, often involving direct physical confrontations between males, leading to the evolution of characteristics that give those males an advantage in these confrontations.