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About 16th of the land on our planet is geographically separate from everything else. Dotting across our oceans and seas are small isolated bodies of land we call islands. Although the loneliness they offer may seem like a negative to us humans, in fact, the shelter islands provide have throughout history created some of the most unique, diverse, and bizarre wildlife this planet has ever seen. The effects islands have on biological evolution are simply all inspiring. From giants to dwarfs to convergence to ancient refugees, islands have it all. This video will highlight some of the amazing biological products of evolution granted by the existence of islands. From Earth's past to present, this is Trade the Explainer's biology on islands.
First, we need to break down why islands are so exceptional as far as their impact on life goes. Islands are unlike continents. They are small and most importantly secluded, surrounded on all sides by ocean. Seclusion from the continents means that only a few selective organisms can exist within their shores. Either from being the original inhabitants that simply became trapped due to rising sea levels or some cataclysmic event or immigrating to the island from the mainland by accident or on purpose via flying, swimming or rafting. The isolation allows evolution a brief chance to really show how much it can do when an organism population is left in a vacuum.
In an ecosystem, organisms will evolve and specialize to fill certain niches or roles in the environment, taking advantage of certain resources to survive. Some organisms might specialize for eating certain types of vegetation. Others might specialize for eating certain other organisms. Through this specialization process, organisms will refine themselves to out compete their rivals, trying to survive by dining on the same resources or occupying the same niche. This process, known as competition, will cause organisms to continually refine themselves by specializing for a specific role until they are more efficient at doing the job than any of their competitors. The ones that can't compete will become extinct. Over time, this process becomes everinccreasingly selective, only allowing the most efficient and specialized for a job to survive. Eventually, one species will have supremacy over a niche with zero rivals.
This process is best analogized to the evolution of machines, such as airplanes. When the airplane was first invented, there were a wide range of designs incredibly distinct from one another. All of them intended to be the best flying machine for the job. However, over time, the most absurd and inefficient flying machines were thrown out and favor the sleeker, more proficient designs. Ultimately, even some of these designs were gradually weeded out to see which ones of them would work the best. The selective process continued as airplanes became more and more specialized for a specific job until we were stuck with a single best design for an airplane, which is used universally. There are different types of this design used for different purposes, but one design holds dominance over all the others.
Competition creates homogeny in both the artificial and natural world. All over the continents, ecological niches, just like airplanes, become standardized. The wide range of designs for a single job seen at the beginning no longer exist. The competition leaves only a single design for a single job by the end. You could say evolution leaves only one distinct winner of a niche in a specific region. And although from this very process we get a wide diversity of organisms specialized for specific roles on continents the process creates uniformity until life all over the mainland is more or less dominated entirely by the same type of organisms. Much like how we have one standardized design descended from a single ancestral design for the airplane. More or less we have one standardized design for an apex predator occupies by a single related group which is ruled on the European, Asian, the Americas and African continents by felids with the fossil record showing that many different unrelated competing body plants once existed. But the competition process only left this single group which was best of all for the single job. This is additionally why continental formations like pangia where a single connected continent exists as opposed to the more isolated ones of today results in less biodiversity. The more connected areas are, the less diversity in the environments there will be.
Organisms on islands function through the same process of competition. But instead of creating one ecosystem where only one group become specialized, standardizing the entire continent, they create many separate but similar ecosystems that allow for many unrelated groups to become individually specialized for allowing for a wide range of experimentation and diversity that would otherwise not exist with the uniformity created by the connectivity of continents. As a result of this, islands can act almost like miniature continents, enabling the birth of very unique organisms seen nowhere else on Earth. They promote evolutionary diversity and prevent uniformity. One can only imagine the diversity an entire world made of thousands of isolated archipelos could bring forth.
The King Kong movie series centers on the fictional Skull Island. The small land mass located in the Indian Ocean is filled with many exotic forms of life, most famously giant versions of animals commonly found on the mainland. Everything from predatory lizards the size of lions to crickets the size of dogs can be found all throughout the island. Most famous is the gargantuan gorilla after which the series is named. The famous literary work Goliver's Travel speaks of an explorer who finds several islands with both miniature and gigantic humans and other animals. Such concepts might seem like complete fantasy. However, the truth is there are literally hundreds of real islands with both giants and dwarves that have existed throughout history. Perhaps not as exaggerated to the extent of movies and books.
Islands can often permit the evolution of giant animal populations that are dramatically smaller on the mainland. Smaller animals such as rats, birds, insects, and lizards end up on islands that often times have few if any predators to prey on them and few competitors to contend with for resources. The lack of predators and lack of competition allows these smaller animals to take full advantage of the island's resources and grow to large sizes as well as fill roles in the ecosystem they otherwise couldn't on the mainland. This phenomena is called island gigantism.
Islands contrastingly can create the opposite effect, causing normally larger animals on the mainland to be dramatically smaller on islands. This can occur as a result of the far more limited resources islands possess. With insufficient food to supply animals with larger stature, animals must adapt to consume less. The limited resources tend to favor neotony, the retention of childlike traits into adulthood, such as a smaller stature in the population. A topic I did a video on previously. This result effect is called island dwarfism. The evolutionary phenomena of islands causing smaller animals to grow bigger and bigger animals to grow smaller is called Fosters's rule or the island rule which illustrates how evolution is impacted by the resources available to an organism population.
Fosters rule has many fascinating examples all across the globe and time. Let's take the remote island of New Zealand. New Zealand sits off the coast of Australia and has been geographically isolated from the rest of the world for 80 million years, meaning the indigenous life that exists on the island broke off all ties long before even the non-avian dinosaurs became extinct. As a result of this, the island is almost completely devoid of mammals. Prior to human colonization, the island was so isolated that the only mammals that existed were seals and bats, which had to fly and swim great distances from their original habitats. The lack of mammals on New Zealand opened up new opportunities for the sheltered inhabitants. With no rodents, hooved herbivores, big cats, canines, or other mammals, many of the traditionally mammal occupied niches were left vacant, ripe for the taking by other animal groups. A large amount of birds were able to migrate from the Australian mainland to New Zealand. Consequently, it became an island exclusively dominated by the descendants of these birds. Many flying species of eagle and parrot diversified greatly to take advantage of the bounty the island possessed. Parrots especially benefited from its isolation, taking on new and bizarre forms never seen elsewhere in the world. A branch of parents broke off and fled to the alpine mountainous territories of the island where they became great predators that mirrored the designs of eagles and hawks from the continent. The Kia evolved a slicing beak and claws used to subdue prey. Additionally, they evolved great intellect and curiosity, and by the time humans arrived, these birds began preying on the defenseless sheep brought to colonize the region.
Other parrots, a close relative to these kas, took a completely different route. The cockapo took advantage of the lack of any ground predators by becoming a herbivore that feasted on the various fruits and plants found on the forest floor. Due to its rich diet, the cockapo was able to grow to a massive size and is now the world's largest parrot. Additionally, it's the world's only flightless parrot. With no need to hide, the cockapo gave up its ability to fly entirely, living its whole life on the forest floor. The sanctuary the island provided allowed the cockapos to live to great ages, possibly the oldest of any bird. However, due to this specialization, these birds were entirely defenseless once humans arrived on the island's shores, introducing many invasive species such as cats and ferrets. Now, the cockapo is almost extinct with only 154 living adults left on the island.
Flightless birds and reptiles, which has been stuck on New Zealand since its original separation from the world, were able to endure and evolve to occupy many traditionally mamalian niches as well. Ratites are the group that encompasses many flightless birds like ostriches and emus. Retites were indigenous to the island since its beginning. With no rats to speak of on the island, something needed to fill the nocturnal scavenger niche. The kiwi was that animal. Just like the cockapo, the kiwis gave up flight to take on their new role. At night, they would come out and feast on various tiny reptiles, amphibians, and insects on the island. Much like the shrews, and rodents on the continents, you can even see in the Kiwi's design and coloration how these animals became the island's bird version of a rat. The kiwi even independently evolved their own whiskers made of feathers. A branch of flightless birds evolved to become the dominant herbivores on the island, dwelling in the forests and grasslands. The moa became giants, standing 12 ft tall; they became the giraffe equivalents of New Zealand. However, even these birds were not undisputed. A type of eagle consequently evolved to prey on these moa. The hast eagle became massive by feasting on such a gargantuan food source. With claws likely big enough to wrap around a human head and a wingspan almost 10 ft wide, these were the largest raptors ever to have existed. Hast's eagle were something right out of the Lord of the Rings, which is ironic considering the movies were filmed in the very place they once roamed. The two giant birds survived as late as the 1400s when over hunting by humans drove both predator and prey to extinction.
Giant insects such as the weda, a relative to the cricket, and the touitara, an ancient reptile that once was widespread during the time of the dinosaurs, but is now only found in New Zealand, also have benefited from the isolation. Only a handful of these original diverse giants that once existed are left on the island today.
Probably the most famous example of island gigantism was the certain inhabitant of Maitius, a small island off the coast of Madagascar. Just like New Zealand, Maitius possessed no terrestrial mammals, allowing it again to be a land belonging to the birds. Pigeons were able to fly to the island and create a population there. From this original stock, some pigeons, just like the para ancestors of the cockapose, decide to become herbivores, feasting on the wide range of fruits, seeds, and nuts found on the island's floor. These birds additionally retain the childlike features of reduced wings, fat body, and juvenile face and beak of pigeons, as they had no need to develop flight due to the lack of predators. The unique appearance of these giant flightless pigeons was so bizarre that when the first humans arrived on the island, they called them by the name that means fatar in its original language. Of course, we know these strange birds today as the legendary and now extinct dodo. Maitius was also home to a large species of near flightless parrot likely similar to the cockapo called the broadbuild parrot and which just like the dodo became extinct very recently. These two birds, like many of the extinct inhabitants of Maitius, are little known, and much of what we know of them comes from a few scattered journals and sketches made by witnesses prior to their extinction.
And it's not just birds that have benefited from the isolation brought by islands. Several reptiles have grown to immense sizes and become menacing predators. In New Calonia, a small island where some of the episodes of the documentary series Walking with Dinosaurs were filmed, the absence of predators has allowed the New Caledonian giant gecko to grow as long as a human arm, making it the largest type of gecko in the world. 40 million years ago, a likely small species of monitor lizard originating in Asia migrated to Australia, where the absence of competing placental mammals allowed them to grow to abnormal sizes. Giant predatory lizards once ruled much of ancient Australia. The largest of which was the recently extinct Megalania. As we now know, all these giant lizards are now gone from Australia, but a few were able to escape and run rampant elsewhere. With the lowering of the oceans during the last glacial period, large stretches of land were exposed across the Indonesian archipelico. A large portion of these giant lizards were able to flee across what was once underwater and colonized the islands off the shore of Australia. While their Australian ancestors died out, these islander lizards became isolated once the sea levels rose again. These dragons, which have evolved to take down animals as big as water buffalo, thrive on a small island chain close to Australia. One of these islands is where we get their name, Komodo dragons.
These dragons actually once existed on one much larger island which was home to even stranger organisms. Flores is a large island to the east of Komodo. In addition to the giant predatory lizards, Flores was home to a giant type of maribou stork that feasted on flesh and was as tall as a man. Still to this day, the island is home to a giant species of rat. However, what was likely the most interesting inhabitants of the island were the dwarves. A subspecies of elephants ended up on the island many millions of years ago. Due to the much scarcer resources, they became dwarfs. An averagesized human could look the elephants of Flores straight in the eyes. There were humans on Flores as well, but these weren't your ordinary humans. Homo Florencis was a different species of human that once shared the same ancestors of us, Homo sapiens. Both of us descended from Homo erectus. However, while one branch of Homoctus remained in Africa and became us, another branch broke off and became stranded on Flores. As adults, these islander humans stood only 3 and 1/2 ft tall, which is why paleontologists gave them the nickname the hobbits after the fictional race of miniature humans in the Lord of the Rings series. These little men used stone tools and likely hunted the miniature elephants on the island as food. However, even these hobbits and miniature elephants were not on the top of the food chain and were likely small enough to be prey items for both the giant lizards and the giant storks. Homo Florianis lived until about 50,000 years ago, meaning it coexisted with the larger modern relatives who would eventually colonize this island and make legends and folktales about the strange wild men that once roamed.
Various ancient islands in the Mediterranean Sea were much like Flores. Several miniature elephants and mammoths existed on islands across the sea. On Cree, the smallest mammoths once lived, and the remains they left might have been the source of many Greek myths of the Cyclops. On what would become Sicily and Malta, you could find swans larger than elephants. Many other mini fans were scattered all across the sea and possibly survived close to the time of man. A painting in the tomb of Rekomire in Egypt depicts what might be a pygmy mammoth, possibly imported from the islands to the north. However, archaeologists are not entirely sure if this is a mammoth or not. It might just be a baby elephant or artistic liberties.
The island of Minorca, like many islands, possessed no predators on them. This lack of predators allowed some animals to lose some traits they developed to combat predators. The island was home to two unique creatures, a giant rabbit and a strange relative of sheep. Nora Logus was the largest rabbit to ever exist. Growing to the size of a dog, the rabbit lost the large ears characteristic of its relatives, probably due to the lack of any threats. Myotragus, a close relative to the sheep, also lived on the same island. It additionally evolved an untraditional appearance due to the lack of predation as well. While most bovids have eyes on either side of their head to spot for predators, Myotraus had eyes facing forward, giving it stereoscopic vision and an oddly humanlike appearance. Myotraus had migrated from a close island and likely competed with Neurolagus for the same food choice, resulting in its subsequent extinction. While Nuralagus died out, Myotraus was able to continue to survive until just 5,000 years ago. Evidence shows that early humans migrated to the island and attempted to domesticate these strange creatures. The remains of adult Myotraus with trimmed and healed horns illustrate a short coexistence with humans until these beasts disappeared entirely.
Madagascar is more like a mini continent than an island. Sitting off the coast of Africa, this island truly is the most unique on the planet. It has been geographically isolated from the rest of the world for 88 million years, meaning the life there has been secluded for a great deal of time. As a result, a lot of life forms here have descended from very primitive animals into due to their separation evolved entirely independently. For example, when Madagascar broke off from India 88 million years ago, all primates were primitive lemur-like animals. Some of these primitive primates were trapped on Madagascar, while many of the ones on the continents evolved into more advanced monkeys and apes. The Madagascar primates continued to evolve independently from the mainland primates, but more or less retained many of the bassil traits of their ancestors. These primates evolved into lemurs. Madagascar practically worked like a time capsule for these creatures, preserving many of the prehistoric features of all primates once had. However, many lemurs continued to evolve into very advanced forms that independently mirrored the evolution of their mainland counterparts. Because Madagascar had no monkeys or apes, many of the roles which they occupied on the mainland were left vacant on the island. Archo Indrris was a species of lemur that was basically the Madagascar equivalent of the gorilla. It could grow as tall as a man and had lost its tail much like apes had did unrelatedly. Archoendras might have survived as recently as 350 B.CE when it was likely hunted to extinction by the newly arrived humans.
Other giants existed on Madagascar as well. The elephant birds were some of the largest birds in history and were around the size of hippos. These birds were closely related to the New Zealand kiwis and could have lasted till the 1700s. Many explorers, including Marco Polo, heard legends of these birds, and one French governor wrote that they sought out the loneliest of places. Just like apes, the absence of cats on Madagascar allowed another animal group to step up and fill the role. A distant relative of the mongoose and Mircat was rafted over to the island around 20 million years ago. And from these colonists, the largest mamalian carnivore on the island evolved to fill the island's panther role. The fussa specialized on consuming lemurs and other mammals evolved so closely to fit the role of big cat on the island. It was originally thought to be a type of cat due to its close resemblance to cougars. Madagascar is also home to some of the smallest animals in the world. The smallest lizard in known history calls the island home. A little chameleon which is downright adorable. All this diversity is owed to the unique seclusion from the outside world the island provides.
Foster's role isn't restricted only to islands in recent history. Several islands in the fossil record from many millions of years ago have also showed this phenomena. The most famous and most unusual of which was the Cretaceous island of Hseg. Fossil beds in Romania illustrate that a large landmass surrounded on all sides by a deep marine basin once existed during the last days of the dinosaurs. The island named Hzg after the nearby town was roughly the size of modern-day Hispanola. It had a tropical climate and topography much like Hina. Unlike its neighboring islands, Het Eggg was extremely isolated. 120 mi from the nearest landmass and possessing exceedingly deep waters on all sides, the island was like a prison, preventing exit and entrance for most of the dinosaurs and other reptiles that lived during that time. As a result, Hedseig had dinosaurs like nowhere else on Earth. Just like islands of recent history, Hedg birthed both giants and dwarves. A plethora of miniature dinosaurs almost identical except in size to their mainland counterparts roamed about the island. Tiny versions of iguanadons the size of dogs ran about. A species of titanosaur, the group of long neck sorapods that were once some of the largest land animals ever to exist were reduced to the size of horses within the confines of hetz.
Other creatures on the island became giants preying on the tiny inhabitants with the absence of any large therapods like tyrannosaurs on the island. A species of terasaur unchallenged became the apex predator. Hi Goper was likely the largest flying animal to ever existed. As tall as a giraffe and with wings as wide as a small plane, Hatsigopter was the undisputed king of Hz. With a body structure much like the Morabu stors of Flores, Hatsigopterex towered over the dwarf dinosaurs of the island which it likely saw as prey. These giraffe stors from hell, as I like to call him, would have made Hezek a horrifying place. Hatsigopter eggs wasn't the only giant on the island. The remains of a giant raptor-like dinosaur were found on the island as well. The creature was very similar in body structure to bird-like therapods such as raptors. But this guy was unique. Instead of having a single pair of signature claws on each foot, they possessed two. For a time, many believe what would be called Baller Bondok was a violent predatory raptor that took a strange, more advanced evolutionary route than its continental brethren. It wasn't until recently that paleontologists actually discovered this animal wasn't a raptor at all, but an early type of bird similar to archaopter that grew gigantic on the island. The doubleclawed weirdo contrasted most proto birds at the time, which were restricted to extremely tiny sizes. In fact, most birds at that time were no bigger than seagulls.
Another island during the Cretaceous also illustrated a strange early evolution of birds. Gargantuis was roughly the size of an emu or ostrich and probably served a role similar to it in its environment. However, gargantuis lived many millions of years before even such animals would ever exist and at a time where most non-avian dinosaurs such as ornithmus occupied many of the niches those birds would one day occupy. Because of this, gargantuas was much like an ostrich mimic that echoed of what was to come in the absence of larger dinosaurs. Almost giving a prediction of the future evolution of birds.
The last island on our journey throughout time and across the earth gives us one last look at how delicate island habitats are and how fragile the life exists on them is. Europosaurus was a type of sorapod from Jurassic Germany. At length, the sorropods of hetz became dwarfs. Its closest relatives were the tallest things that would ever walk the earth like giraffitan and brachiosaurus. But when we compare the two skulls side by side, the effects of islands are striking. The miniature soraods lived for a time, but became extinct. Paleontologists would later learn the fate of these mini sorapods with the discovery of tracks, illustrating a drop in sea levels, creating a land bridge to the island, breaking a likely millions of year-long embargo. The footprints of a large theropod dinosaur crossing the bridge and entering the island were found. With no defense, the many sorapods were hunted to extinction by the invaders. Much like Gigant Avis, the islands of the past echo the fate of the islands of the future.
Today, a two-legged invader once again threatens the unique biodiversity on islands. This time across the globe. The only difference is that the invaders this time can be reasoned with and stopped. Almost all the organisms that have become extinct in recent years were islanders. From the mythical Moa to the famed dodo. But this doesn't have to be the case. Let us preserve these sanctuaries of strange life so that they can continue to be beautiful lands of natural evolutionary experimentation, often yielding some of the most unique life forms this planet has ever seen. And on that note, thanks for watching. The founders dreamt of this island. Our ships landed on it shore.