Examining the Many Quirks of the "Island Rule"
The unique evolution of island species has challenged science since the time of Darwin. For years, biologists have recognized that island animal populations tend to acquire different sizes than their mainland counterparts. Examples of such dwarfism or gigantism include the giant tortoises of the Seychelles islands, Indonesia's Komodo dragons, and the boas of the Belizean Snake Cayes.
Both larger and smaller sizes have some innate advantages. Big creatures have a wider choice of food and tend to dominate others of their species. Smaller creatures, on the other hand, need fewer resources to survive—which may be important in the more limited ecosystems of many islands.
Perhaps the first attempt to explain these developments was a 1964 paper published in Nature entitled, "Evolution of Mammals on Islands," prepared by a young biologist named J. Bristol Foster. Foster's research led him to theorize that large mammals tended to evolve to smaller sizes after colonizing islands, and smaller mammals tended to grow larger. His generalizations became known as the "island rule," and were soon followed by the landmark 1967 book The Theory of Island Biogeography by Robert H. MacArthur and Edward O. Wilson.
Though it represented an important step into little explored scientific territory, the "island rule" is riddled with exceptions and unanswered questions. The same animals, for example, sometimes grow to large size on some islands but not on others. Certain islands also exhibit both gigantic and dwarf forms of various reptile and lizard species. The reasons for such variations are a matter of fascinating debate—and a promising field for many researchers like Boback.
The riddle of the Belizean boas may have its origins in the complex and unique ecosystems of the Snake Cayes, within the genetic makeup of the reptiles themselves, or perhaps a combination of both. Either way, snake wrangler Scott Boback hopes that his research can provide the key.
This adventure in the National Geographic Channel's Snake Wranglers series, The Boas of Belize, airs in the United States tonight, March 14, at 7.30 p.m. Watch snake researcher Scott Boback as he investigates the boa constrictor stranglers found on Belize's mainland and islands.
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