Barnacle Project
At school we are doing a project on the discovery of Evolution. (October 2010)
I was interested in the evolution of Galapagos Tortoises. These magnificent creatures can weigh up to 570 pounds, and are some of the most versatile and unique creatures I have encountered. I found out that naturalists think that the first Galapagos Tortoises probably first arrived at the islands by clinging onto driftwood from a river mouth on the South American Continent. There is proof; a relatively big tortoise that lives on the South American mainland is related to the Galapagos Tortoise. The original 'immigrants' landed on San Cristobal and afterwords moved to the other islands and soon there were 15 subspecies (as of Darwin's time). However, sailors prized the tortoises for their meat and easiness of care onboard the ship. Because the tortoises would stay alive onboard for a year with little or no food, sailors would try and get as many onboard as possible. Now, there are only 11 subspecies left. The individual species evolved into the separate groups because on different islands the climate was different, and by a process of natural selection (in where the tortoises who survive more easily will produce more offspring). For example, the domed shells in species who can graze in big meadows of grass, whereas the saddle backs have an easier time getting food slightly off the ground, like bushes or cacti due to their longer necks and saddle-shaped shells. And then there is the intermediate-shelled tortoise (it's not called that, but you get the point) and it had a shell that is more saddle-shaped then a domed shell but not as pronounced as an actual saddle backed tortoise. With the evolution of the turtles that survived better, the lifespan of these tortoises grew. The current record for oldest Galapagos tortoise was a female tortoise at the Australian Zoo that was at least 171 years old! That is an amazing feat of evolution, and also how the tortoises adapted when they went from island to island. Sadly, all this evolution was being eradicated once pirates and other sailors took the tortoises. Once they were low in numbers, the fishermen working the waters off the coast of the islands brought in feral goats, who immediately started eating all the vegetation and multiplying as quick as the wind. The fishermen then used these goats as sources of meat when they were sailing. Eventually, we estimate that about 200,000 of these poor creatures were killed for these purposes. Now, many zoos and the Charles Darwin Research Station on Santa Cruz Island in the Galapagos have breeding programs for these tortoises. For example, the San Diego Zoo contributed their male Hood Island Tortoise (Species name: Geochelone nigra hoodensis) to a breeding program for Hood Island Tortoises (which are very rare in the wild) at the Charles Darwin Research Center. He has fathered hundreds of tortoises and is one of many in a key role in restoring the natural habitat, species and welfare of the Galapagos Islands. A fun fact about how tortoises have 'showdowns' where the dominant male gets his choice of a female mate. The two tortoises will stand next to each other, and whoever can raise his neck higher wins, even if he is smaller than the male who's neck is shorter. Thank you for reading my short essay about the Galapagos Tortoises.
Bibliography
http://www.galapagosonline.com/nathistory/wildlife/animals/tortoise.htm
http://www.sandiegozoo.org/animalbytes/t-galapagos_tortoise.html
http://www.all-about-reptiles.com/galapagos-tortoise.html
http://www.sandiegozoo.org/animalbytes/t-galapagos_tortoise.html
http://www.all-about-reptiles.com/galapagos-tortoise.html