Spiders of the World

Background For This Exercise

"Hello, My name is Dr. Rosemary Gillespie. I am a professor in the department of Zoology at the University of Hawaii. I am interested in how organisms form new species, and am using spiders to look at this question. In particular, I am asking: How do spiders differentiate, and how is species formation related to isolation between populations, and differences in the habitats that they occupy."

"I chose to work in Hawai`i because it has a number of virtues that make it perfect for looking at these kinds of questions. First, it is the most isolated archipelago in the world, formed by volcanic activity under the ocean. What are the chances of an animal getting out here -- thousands of miles in the middle of the ocean -- and managing to survive AND reproduce once it got here? It's surprising that any animals and plants made it here. But the few that did were rewarded: They were presented with a "clean slate" so to speak: A nice warm environment with lots of different habitats."

"The spiders that made it here did so by ballooning -- letting out silk, and taking off in air currents, much like Mary Poppins with her umbrella. by chance the air currents blew them out in the Pacific, and by chance dropped them on the Hawaiian Islands. The few spiders that survived these unlikely events belonged to a small group of mainland genera. On encountering the islands, virtually free of other spiders, these few genera diversified by what is know as adaptive radiation, when many species are formed from a few ancestors. In particular, a spider in the genus Tetragnatha, which came from a lakeshore existence on the mainland, has formed species in almost every available habitat in the islands: You now find some species that live in the rain forests, some on old lava flows, some in high drier areas. ...So you can look and see how habitat is related to species formation."

"Another really nice thing about Hawai`i is that the islands are continually forming by volcanic activity. Once they form they move northwards. So, as they are now, the islands are arranged in a chronological order, with the oldest island (Kaua`i) in the north, the youngest island (Hawai`i) in the south. Species colonize these islands as they form. So they are still colonizing the young island of Hawai`i, and have had only a short time to form different species. However, they have had much longer to form lots of different species on Kaua`i. So species on Kaua`i are often more specialized, with more restricted ranges, while species on Hawai`i often have broader ranges and are more generalist."

Spiders of the World


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