Sexual dimorphism essays

Sexual dimorphism essays Darwins theory of evolution, natural selection, plays a role in the sexual dimorphism of purple-throated caribs. Natural selection directly alters the frequency of phenotypes. For natural selection to occur there must be variation of a trait among the individuals. Secondly, the trait must be able to be passed down from one generation to the other. Thirdly, there must be differential reproductive success, meaning that one trait will survive to be passed on more often than the other. Sexual dimorphism is the difference in trait between different sexes of the same species. The female hummingbirds bills are longer than the males and are curved at 30 degrees, compared to that of 15 degrees of the males. Such sexual dimorphism evolved through the ecology of feeding; the difference in bills enables both sexes to eat different foods. The only food plants available to the caribs are red-bracted H. caribaeas and green-bracted H. bihais. Both sexes differ in the way they use the two species. T he males are more settled and tended to control and defend the densest stands of H. caribaea, which bears three times as many flowers as H.bihai. Females behaved differently. Because females have to incubate eggs and raise offspring without male assistance, they cant guard flower patches and therefore must feed from undefended patches. The females smaller size prevents them from competing successfully against males for the richest territories (H. caribaeas). Now that we know what plants each sex feeds on, the differences in flowers of the two species of plant will explain why the bills of the sexes are different. The H.caribaea flower, dominated by male pollinators, is shorter and straighter than the flowers of H. bihai. They are shorter than the H. bihai flower by six millimeters, which is also how much the males bill differs from the females. The H. caribaea flowers are curved at a 20 degrees arc, which suits the males&...