Final answer:
Trivers' principle expands on Bateman's by suggesting that the sex with higher parental investment (often females) is more selective, while the less investing sex (usually males) competes for mates. Sexual selection thus results in different strategies for males and females, leading to sexual dimorphism.
Step-by-step explanation:
To distinguish Trivers' principle from Bateman's principle, we must understand their takes on sexual selection. Bateman's principle posits that, because females generally invest more energy in producing and caring for offspring, they are more selective in mate choice. Males, on the other hand, can enhance their reproductive success by mating with as many females as possible, making them less selective but more competitive.
Trivers' principle, also known as parental investment theory, extends upon this idea by suggesting that the sex which invests more in the offspring (usually females) will be more selective when it comes to mating. On the contrary, the sex that invests less (typically males) will compete for access to the high-investing sex to maximize their reproductive success.
These principles suggest that sexual selection operates differently in males and females, with females being choosier and males being more competitive and showing off traits that signal their desirability, such as large body size or elaborate ornaments. This can lead to sexual dimorphism, where males and females of a species show distinct physical differences not related to their reproductive organs.