A male saddleback tortoise from Pinz&#243;n Island<br /> reaching for an Opuntia cactus pad. As a result of natural selection on islands in the Gal&#225;pagos where tortoises are found, Opuntia have<br /> evolved into tree forms, reaching a height of 12 meters. On islands where tortoises have never been present, Opuntia form clumps along the ground,<br /> reaching a maximum height of only 2 meters. The close relationship between cacti and tortoises represents a classic case of coevolution. Photograph<br /> by the author.
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