Arriving to the archipelago was only part of the challenge for life in the Galapagos. Once they landed, the new arrivals had to find a way to survive and reproduce on the desolate volcanic islands.
The first inhabitants
The Galapagos Archipelago was not always the rich, living laboratory that we know it as today. When life first arrived on the islands, they were entirely void of living organisms; instead, the archipelago was a barren wasteland of volcanic rock. Thus, the process through which the ecosystem formed was slow and difficult.
Experts believe that bacteria and small plant spores were the first form of life to take hold on the Galapagos Islands. Pioneer plants, such as algae, ferns and lichen dominated initial stages, slowly giving way to richer biodiversity. Pioneer plants are able to thrive in limited organic material and hostile conditions, as they can produce their own food simply through sunlight, water and air. But, perhaps more importantly, they are an essential aspect of young ecosystems, as they increase soil fertility and create microclimates suitable for less hardy seedlings. For example, lichen is able to grow on the surface of rocks, eventually breaking it down to form soil. Other pioneer plants inject nitrogen into the soil through a process known as nitrogen fixation. Furthermore, as the plants die they leave behind organic matter, adding nutrients to the land. The Lava Cactus, endemic to the islands, is one of the more common pioneer plants in the Galapagos.
As the soil becomes thicker and richer, less resilient, more complex and larger plants are able to grow and, over time, a more diverse habitat forms. As the soil becomes more fertilized and vegetation increases, herbivores such as tortoises and iguanas, inevitably followed by carnivores, are able to survive and establish a population, further developing the new ecosystem.
Adaptive Radiation and Diversification
Despite the young age of the archipelago, its isolation and its imbalance of fauna, the Galapagos is in no way lacking species. Indeed, the Galapagos Islands have an extraordinary high rate of endemism. From lichens to rats to iguanas to giant tortoises, endemism is high in all species found on the islands. 80% of land-based animals are endemic, while 20 of the 22* reptiles, one third of the 600 plants and 20% of inshore marine species are endemic. Among these are the flightless cormorant, marine iguana and giant Galapagos tortoise.
The fact that numerous species can be found in the Galapagos Archipelago is thanks to the combination of the islands’ unique location, adaptive radiation and natural selection. From arid to humid, marine to terrestrial, the Galapagos Archipelago has a varied range of natural habitats including coral reefs, highland forests, and sand dunes. This is largely due to their position along the equator, as well as the Humboldt and Cromwell ocean currents flowing by. The diverse ocean conditions (temperature, nutrients) promote a variety of microclimates, which support a diverse ecosystem.
As a result of the multiple habitat zones, as a population spreads it is likely to come across a new niche that is different from the one that it had evolved for. In order to better exploit the niche (available diet, environment, etc.), the species is able to develop slight variations over just a few generations and, indeed, these can be so extreme that a new species is formed. This process is called adaptive radiation. (The most famous example of this is Darwin’s Finches, in which at least 13 species evolved from the original ancestor to the islands.) Those that best adapt to the niche will have the greatest reproductive success and push out the weaker species through a process known as natural selection, forcing the other to evolve or die. It is because of this that such a rich ecosystem was able to form from the limited number of species that arrived and established themselves on the Galapagos.
This process happens everywhere in the world; however, because there were (before the arrival of humans) very few external influences and limited species in the Galapagos, the animals were able to adapt to each niche as necessary, some undergoing tremendous diversification. For this reason, the island and its diverse habitat zones have become a unique laboratory for scientists, captivated by the clarity in which these evolutionary processes occur.
*Information may vary, it is based on average.