SOUTH PLAZA ISLAND, GALAPAGOS, ECUADOR - MARCH 2007: A photographer lines up a telephoto shot of a land iguana on South Plaza Island. These iguanas are totally unique to the Galapagos and have been driven to extinction on many of the islands. On South Plaza Island, however, evidence indicates that their numbers have become too great, and they are actually threatening the cactus poplulation. The iguanas feed on cactus flowers, leaving the plants no way to procreate. The number of cacti on the island has plummeted in the last 20 years. Yet another sign of an ecosystem under great stress. (Photo by Eric Rorer/Aurora) (release code: 0008)