Island Evolution

The elephant bird may well be the largest bird to ever walk the earth. And it also laid the biggest bird eggs in history. The elephant bird was native to Madagascar. The giant bird had no natural predators on the island, meaning it could afford to lay one egg per year and take good care of it. This egg would be left undisturbed and its chick (a sturdy little fellow in its own right) had excellent prospects of survival. On the mainland, there are far more predators that have designs on your nest. That’s why birds there often lay more than one egg. So that even when only a few eggs hatch, they are able to spread the risk. Rene Dekker briefly explains this principle in the accompanying video clip. The elephant bird probably became extinct somewhere around the year 1000, when man first came to Madagascar.
The egg of an elephant bird, Aepyornis maximus. This specimen was collected on Madagascar by the 19th-century explorer Alfred Grandidier. The egg is 29.7 cm long, 20.5 cm wide, and its shell is 3 mm thick.

On the island of Gargano this relative lived from the hairy hedgehog, but then without spines and probably with a lot of hair. Growing up on an island has several advantages, such as the fact that it is harder for predators to catch you. And there is another advantage. Small animals have little body content and therefore a relatively large skin surface, which means they lose a lot of heat. To keep their energy well balanced, they have to eat all day. Larger animals need less food to stay warm. So the large specimens of small animals have an evolutionary advantage, so that small hedgehogs eventually grow up on an island. The giant hedgehog was endemic to Gargano, which means that the animal was found nowhere else. During the later ice ages, the sea level dropped, making the island close to the mainland and the hedgehog extinct.

This little five-horned prongdeer was another native of Gargano. The animal had a pair of pronged horns above each eye, as well as a horn on its nose. Fossil finds show that these prongdeer existed in a range of sizes. Smaller and larger species lived side by side on the same island, with each fulfilling its own role in Gargano’s ecosystem. And none of them were bothered by predators, meaning that the deer could preserve their striking five-horned skull shapes. This particular deer is a lot smaller than its modern-day relatives – another example of the ‘island rule’.

You probably know him: the dodo! This bird is world famous because it is no longer there. You are vulnerable on an island. As soon as new animals set foot ashore, you are exposed to danger that you are not prepared for. If you are not used to enemies, it can be over quickly. That is also how the dodo in Mauritius fared. The dodo was a pigeon-like one that could no longer fly. That too is an adaptation to island life: he simply no longer needed to choose the sky. When the first people arrived on the island in the 16th and 17th centuries, they brought rats, monkeys and pigs into their ships. What exactly happened is unknown. But the dodo did not flee and did not protect its eggs, which could easily be stolen. With the last dodo the whole species died out. This was the first time that an animal died out at the hands of humans, which is why the dodo has become the icon of extinction.

Lakes can be considered islands too, since as isolated habitats, no species can leave or enter these bodies of water. At Lake Victoria in Tanzania, the Naturalis researchers have been able to experience the lightning-fast evolution of fish species up close. Lake Victoria’s cichlids form a classic illustration of the evolutionary process, thanks to their ability to swiftly adapt to changing circumstances. Examples of such adaptations include the shape of their teeth, the size of their eyes and the animals’ variety of body shapes.

Island species are still dying out today. These wonderful minute snails live on the limestone hills of Malaysia. The animals that manage to reach these hills become entirely isolated from the main group and evolve into a variety of endemic species. As a result, many of the snails found on these slopes only live on that particular hill – nowhere else. But now, these hills are being excavated for their limestone. And these tiny snails disappear together with the hill they live on – although we still discover new species from time to time.