The Arrival of Native Species in the Galapagos Islands
Scientists agree that the Galapagos Islands never connected to the mainland. Thus, the ancestors of every plant and animal species native to the islands arrived in the archipelago from somewhere else. Despite a separation of hundreds of miles from the mainland, most of the animals in the Galapagos originated from North, Central and South America and the Caribbean. Land birds and California sea lions arrived from North America, and pink flamingos and Darwin’s finches arrived from the Caribbean. Land iguanas, giant tortoises, pelicans, cormorants and boobies all arrived from South America. Fur sea lions and penguins came north thousands of years ago as a result of the Humboldt Current from the Antarctic. Animals that were not so adaptive to the ocean, such as land mammals, had to wait until passage was provided by human vessels.
Today, most scientists accept the theory of long-distance dispersal for bringing life to the Galapagos Islands. It is hard to imagine that so many organisms could endure the hazardous voyage, survive in an unfamiliar environment and reproduce. Flotation rafts of natural vegetation, wind and air currents and oceanic drift all contributed to this “sweepstakes dispersal.” Birds displaced from their migratory routes also landed on the islands. Sea birds carried seeds and invertebrates on their feathers and in their digestive tracts. When they deposited this “cargo,” new colonies took root.
Many animals are not found in the Galapagos. Amphibians and other aquatic animals, for example, are poorly represented. Large terrestrial mammals also failed to make the crossing. The lack of herbivorous mammals left a niche open for tortoises. These huge reptiles developed and became the large grazing herbivores on land—a position they enjoyed until the relatively recent arrival of humans with domestic livestock.