The Galápagos Islands are a volcanic archipelago isolated in the Pacific Ocean, fostering a remarkable concentration of biological diversity. This unique living laboratory, famously visited by Charles Darwin in 1835, provided foundational evidence for the theory of evolution by natural selection. Assigning a single number to the species count is challenging because the total depends heavily on the definition used by scientists. The archipelago’s ecological importance lies in the large proportion of species that have evolved to be entirely unique to the islands.
Defining the Count: Native, Endemic, and Introduced Species
The total number of species cataloged in the archipelago, including insects, invertebrates, and microorganisms, is estimated to exceed 9,000 confirmed species. However, the focus for conservation and evolutionary studies typically centers on vertebrates and vascular plants. Scientists use three distinct classification categories. A species is considered native if it arrived naturally without human assistance, but is also found in other regions of the world.
A species is categorized as endemic if it is found exclusively in the Galápagos and nowhere else, a category that includes over 1,500 species of animals and plants. This high rate of endemism is the archipelago’s defining biological characteristic, with approximately 97% of reptiles and land mammals, and over 80% of land birds falling into this classification. Conversely, introduced species are those brought to the islands by human activity, intentionally or accidentally, and these pose a major threat to the native ecology. Approximately 1,639 introduced species have been recorded, which often compete aggressively with the delicate native flora.
Terrestrial Wildlife: Iconic Land Animals
The most famous terrestrial inhabitants are spectacular examples of evolution in isolation. The Galápagos giant tortoise, for which the islands are named, has evolved into twelve surviving subspecies, each with distinct shell shapes adapted to their local environments. Tortoises on islands with high, humid vegetation possess large, dome-shaped shells. In contrast, those on drier islands developed a saddleback shell, allowing them to stretch their necks higher to reach sparse vegetation like the prickly pear cactus pads.
Another powerful illustration of adaptive radiation is seen in Darwin’s finches, a group of about eighteen species whose common ancestor arrived from the South American mainland. These birds diversified rapidly, primarily distinguished by the size and shape of their beaks, which specialized for different food sources such as seeds, insects, and cactus nectar.
The land iguanas are a related group of endemic reptiles, which include the common yellow land iguana and the extraordinarily rare Pink Land Iguana (Conolophus marthae). This unique pink species, confined to the slopes of Wolf Volcano on Isabela Island, was not officially recognized until 2009. Its coloration is due to a lack of skin pigment, which allows the blood underneath to show through. Genetic analysis suggests this lineage diverged from other land iguanas around 5.7 million years ago, making it one of the oldest known divergence events in the archipelago.
Marine Biodiversity and Coastal Life
The surrounding Galápagos Marine Reserve is an area of intense biological activity, supported by the convergence of cold, nutrient-rich currents with warmer tropical waters. The marine environment hosts a variety of unique species, including the world’s only swimming lizard, the marine iguana. This reptile feeds exclusively on marine algae, using its powerful claws to cling to submerged rocks while grazing.
To manage the high salt content ingested with their diet, marine iguanas use specialized glands in their noses to filter and expel excess salt. Another remarkable endemic is the Galápagos penguin, the only penguin species that lives and breeds north of the equator. Marine mammals are also represented by the endemic Galápagos sea lion and the Galápagos fur seal.
The underwater realm includes numerous endemic fish species, demonstrating the depth of this isolation. While not endemic, the waters are also home to large seasonal aggregations of scalloped hammerhead sharks, which gather in enormous schools, a behavior that draws global attention.
Flora and Plant Life Uniqueness
The plant life of the Galápagos exhibits a high rate of endemism, with more than 30% of the native plant species found nowhere else. The islands’ varied elevation creates distinct vegetation zones that support different plant communities. The arid lowlands near the coast feature species adapted to dry conditions, such as the endemic cacti.
The prickly pear Opuntia is particularly noteworthy, having evolved into a tree-like form on some islands to escape herbivory by giant tortoises and land iguanas. The moist highlands support a very different ecosystem, dominated by the Scalesia tree, often called the “Galápagos Daisy Tree”. This genus of fifteen endemic species is a spectacular example of adaptive radiation in the plant kingdom, as it evolved from a small daisy-like ancestor into tall trees that form dense forest stands.