Terrestrial organisms on the volcanic islands of the Galapagos are all progeny of organisms brought in by sea currents, air currents, or birds from the continent or other lands. Because the islands are about a thousand kilometers distant from the continent, unique evolution has taken place on the islands. Consequently, many endemic species evolved, leading to the ratio of endemic species at 52% for terrestrial anthropods, 96% for terrestrial snails, 100% for terrestrial reptiles, 89% for terrestrial mammals, and 51% for seed plants. Well known endemic species include the Galapagos giant tortoises (13 subspecies); two species of land iguanas, the marine iguana; the Galapagos penguin; Galapagos the flightless cormorant; 13 species of Darwin's finch; Scalesia, an arboreous plant of Compositae (15 species); and eight species of three genera in Cactaceae.

Galapagos giant tortoise Land iguana Marine iguana Galapagos penguin Flightless cormorant
Darwin's finch Scalesia
Lava cactus Prickly pear

There are three major ecosystems in the Galapagos Islands: terrestrial, coastal, and marine. The terrestrial ecosystem forms a zonation reflecting increases in precipitation from the lowland to the highland, covering the Littoral Zone influenced by the sea to the dry lowland zone, transition zone, moist highland zone, and high-altitude fern-sedge zone. The three ecosystems exhibit characteristic behaviors in years of El Nino. In the terrestrial ecosystem blessed with high precipitation, plants proliferate to bear flowers and fruits; herbivorous insects and birds reproduce abundantly; and carnivorous birds feeding on small animals thrive. In contrast, high water temperature eliminates seaweeds along the shores, making marine iguanas that feed on the seaweeds hungry and unable to reproduce. Moreover, the disappearance of shoals makes sea birds, sea lions, and fur seals unable to reproduce, and brings their mortality rates up. Nearly the opposite esponses are observed in years of La Nina.