The Hidden World of Islands

Scattered throughout the sprawling expanse of the ocean are isolated pinnacles of land. Mountains that emerge from the endless blue, exposed to the unyielding elements of the high seas. But these battered and beaten monuments create boundless opportunities for new life, and lay the foundations for complex ecosystems that bloom from the jagged cliffs. These are the islands of the open ocean. Havens for the lost and the stray, where animals are no longer limited by the constraints of life on the mainland. On these lonely shores, evolution runs wild, and allows creatures to diverge into the beautiful and the bizarre. Let's head ashore, and explore the life of these hidden worlds. Islands make up a sixth of all land on Earth. In the Pacific alone, more than 25,000 islands are scattered amidst the endless blue, from mountainous rocks to coral atolls, each hosting unique communities of life and species found nowhere else on Earth. Ecosystems that would not exist if not for the powerful forces that pulled these mighty rocks from the abyss. The birth of an island is a slow but violent process, for they are formed from fire and smoke. Volcanism, piling up lava on the seafloor to create a seamount that rises up out of the abyssal plain. Over time, the seamount's elevation grows higher and higher, until it breaks through the water's surface, with the volcano's peak becoming an oceanic island. Much of an island's life is spent at this stage. Some endure like this for millions of years, giving plants and animals time to arrive and adapt to a life in isolation. But in the long term, these islands provide only a temporary haven. An extinct volcanic island is unable to lay more stone atop its monument. Time sees their rugged cliffs and weathered shores crumble into the sea. The islands diminish. But this is not the end of their story. As the mountains recede into the ocean, coral atolls form from their battered bones. Ring-shaped, sturdy reefs that shield a central lagoon within from the forces of the open ocean. An entirely different community now has the opportunity to thrive. Around the island of Bora Bora in the South Pacific, a lagoon and a thick coral reef provides sanctuary for young creatures, safe from the predators that stalk the open ocean. In the case of both atolls and islands, their isolation provides new opportunities for life to thrive. For an island to become host to any kind of ecosystem, life must first find a way to reach its shores. There are a few mechanisms by which plants and animals make this staggering journey. Wind is essential, for it picks up spores from ferns and mosses and carries them thousands of miles out to sea. These are pioneer species that settle upon the rocks and begin the process of ecological succession, only able to survive here due to their tolerance to the extremes. Upon their arrival, barren, lifeless rocks begin to bloom. In Hawaii, the volcanic mountains experience succession at different rates, depending on their exposure to wind. The windward side of Kilauea Volcano is teeming with thick forest. But the leeward side, facing away from the wind, endures as mostly barren rock. Migratory birds are brought to new islands as they traverse the skies above the waves, while marine animals drift here at the mercy of the ocean's currents. Sea turtles and crabs, unimpended by the sea, are often the first animals to crawl onto new land, drawn by the need to find a place to nest. As more and more life convenes at these remote shores, a climax community gradually forms. Rather than the once barren rocks being covered in mosses and lichens, they now host sprawling forests. Alive with the call of birds, and the rustling of animals in the undergrowth, you only have to compare the life of Hawaii's oldest and newest islands to observe this process. Isolated from the mainland, a new island provides a unique habitat for life. With its own set of conditions, life that arrives here can evolve differently. Over time, they transform to create new species that display an astonishing variety of traits. Isolation drives speciation. This process, in which organisms diversify rapidly from ancestral species, is called adaptive radiation. On islands, it arises from the unique resources available, and the new biotic interactions that in turn open new niches. The only way to survive in unfamiliar worlds is to adapt quickly. In the Galapagos Islands, 13 species of small land birds called Darwin's finches are a classic example of adaptive radiation. Their common ancestor arrived on the Galapagos about 2 million years ago. Since then, they have diversified into 15 new species, each different in terms of body size, beak shape, song, and feeding behaviour. With so little competition to hinder their evolution, the finches were able to exploit numerous different lifestyles or niches. The Galapagos Islands are also home to communities of giant tortoises, as well as the peculiar marine iguana. The only iguana on Earth to feed exclusively underwater, with short blunt snouts and sharp teeth that help them scrape algae off the rocks. Flattened tails allow them to swim with ease like a crocodile, while long sharp claws let them cling to rocks in heavy currents. It is believed that they adapted to a seafaring life from land iguanas around 4.5 million years ago. An event only made possible by the abundant food found in the waters that surround the islands. We'll explore why this is the case later on in the video. As shown by Darwin's finches in the case of marine iguanas, islands create a scale model of evolution. Populations on different islands experience a different set of selection pressures, so they change in different ways. But despite the divergence that arises from a life in isolation, there are a number of traits that seem to reappear time and time again. Animals on opposite sides of the Earth independently evolving similar traits as a result of having to adapt to similar environments. This process is called convergent evolution. When the early ancestors of lemurs arrived on Madagascar, they found themselves on an island rich with diverse habitats, abundant resources, and very few competitors. Adapting to these new and ideal conditions triggered the evolution of over a hundred species found nowhere else on Earth. Perhaps the most bizarre creature to arise from this was the aye-aye, a primate that behaves like a woodpecker. Because woodpeckers have never called Madagascar home, the aye-aye evolved to take advantage of its niche instead. Large incisors for gnawing at bark mirror the long, sharp beaks of woodpeckers. A special elongated finger allows the aye-aye to reach deep into the trunks of trees to get at grubs that other lemurs can't get to. It traded in the strong back legs and agile bodies of its cousins for an entirely different, but equally efficient lifestyle. Islands create opportunities for life beneath the surface, as well as above the waves. Off their shores, shallow submerged land is a key foundation for coral reef ecosystems. Tropical corals will make the most of any solid surface that provides access to the sunlight zone. In addition, wherever there is a landmass in the open ocean, currents and circulation patterns change. Nutrients from colder, deeper waters rise towards the surface, creating a world of abundant food. This is known as the island mass effect. At the Galapagos Islands, the cold Humboldt current flows north from Antarctica, bringing nutrient-rich water and helping sustain the rich marine biodiversity. The nutrients feed plankton and plants, and the entire ecosystem blooms from there. The sheer quantity of nutrients from dead and decaying matter carried by this current makes it one of the most productive ecosystems in the world, and it is the reason why penguins can be found on the equator. The Galapagos penguin, orcas, and sea lions, along with other creatures that typically reside further south, are supported in the Galapagos Islands by the year-round supply of fish and cold waters. Around many oceanic islands, mangroves dip their roots into the shallows, and play important roles in local ecosystems. They provide ideal breeding grounds for fish and crustaceans, while juveniles find shelter among the roots. Coral reefs are often found in concert with seagrass beds and mangrove forests around oceanic islands. The mangrove trees trap sediment and pollutants that would otherwise flow out to sea. Seagrass beds act as an additional barrier to silt and mud that could smother the reefs and kill the corals. In return, the reefs protect the seagrasses and mangroves from being battered by the strong ocean waves. Without mangroves, the productive marine ecosystem around islands would collapse. Together, island ecosystems are a pillar on which much of the ocean's biodiversity is dependent. In providing a foundation for corals, and a sanctuary for juveniles, islands nurture life in the oceans in its early stages. The same is true of their terrestrial ecosystems, with islands providing boundless opportunities for evolution to run wild. But in the end, it is the stability of islands that allows life to thrive to such an extent. They are formidable monuments, on which life can depend for protection, nourishment, and opportunity. Today's video is sponsored by Blinkist. If you've ever wanted to read a book but just can't find the time, then this app is for you. 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