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By LOLAJANE
01/25/2010 - 03:48:14

Type: Spaceship
Rating: 0.07 (Not rated)
Tags: dimorphism, hummingbird, lolajane, mcdarwinchallenge

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Description

Sexual dimorphism is the difference in form between different sexes of the same species. Charles Darwin, in 1871, advanced the theory of sexual selection, which related sexual dimorphism with sexual selection. His theory offered three explanations for the evolution or sexual dimorphism: courtship for breeding; fecundity or reproductive capacity; and ecological causes, for example partitioning resources to reduce competition for food between the sexes. The first two examples of the theory were easy to prove because there are so many well known examples. However, examples of ecological sexual dimorphism are much harder to find. Finally in 2000, Ethan J. Temeles, Professor of Biology at Amherst College, proved that ecological sexual dimorphism existed in the Purple-Throated Carib Hummingbird.
This female Purple-Throated Carib Hummingbird illustrates ecological sexual dimorphism. The Purple-Throated Hummers, about 4.5 inches long, are found on most of the Lesser Antilles Islands but nowhere else outside that area. While both male and female P-TC Hummers are almost identical in color, there are significant physical differences: weight, males average 8.6% heavier than the females; wing-span, males average 25% more; bill length, females bills average 20% longer; bill curvature, females average 40% more curvature than males. Like most types of Hummer, they get protein by feeding on insects. However they feed on nectar only from certain species of Heliconia flowers. The females feed on completely different Heliconia plants than the males are able to feed on. The P-TC Hummers are the exclusive pollinators of their preferred Heliconia. The Heliconia nector is found in the bottom of small flowers inside the outer brackets of the Heliconia Plants. Female P-TC Hummers, with their longer and more curved bills, feed on nectar that the males can?t reach with their shorter and straighter bills.
Links: http://en.wikipedia.org/wiki/Charles_darwin; http://en.wikipedia.org/wiki/Sexual_dimorphism; http://www3.amherst.edu/~ejtemeles/hummingbirds.html