Final answer:
The mammalian species with the greatest relative variance in adult size is the marsupial mammal. Male marsupials tend to be larger than females, and dominant males usually have an advantage in mating. This is seen in species like kangaroos, elephants seals, elk, lions, and non-human primates.
Step-by-step explanation:
The mammalian species with the greatest relative variance in adult size is the marsupial mammal.
In marsupials, there are significant size differences between males and females, a trait known as sexual dimorphism. Male marsupials tend to be larger than females, and dominant males are usually the largest or best-armed.
This is seen in species like kangaroos, elephants seals, elk, lions, and non-human primates. So, among mammalian species, marsupials have the greatest relative variance in adult size.