Islands are a kind of pressure cooker for evolution. it’s adapt or die. On isolated places live species that are found nowhere else on our planet. And they can occasionally look quite freakish.

Eilandevolutie
Islands are a kind of pressure cooker for evolution. Evolution is the process through which animal and plant species adapt to changing circumstances, with natural selection as a key mechanism. And this can lead to bizarre results when species are confined in a limited space with few predators to keep them in check. You can’t run from floods, for example. You need to compete with other species for a limited supply of food. And you’re unable to migrate to warmer or colder areas. Indeed, evolution often proceeds at a higher pace on islands than on the mainland. Which is why islands are a rewarding source of information for many Naturalis researchers. After all, it’s adapt or die. And on an island, this often equals extinction, because here, you can encounter species that are found nowhere else on our planet. And they can occasionally look quite freakish.

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.

Op het eiland Gargano, de spoor van de laars van Italie, leefde dit familielid van de haaregel, maar dan zonder stekels en waarschijnlijk met veel haar. Groot worden op een eiland heeft verschillende voordelen, zoals het feit dat roofdieren je moeilijker te pakken kunnen krijgen. En er is nog een voordeel. Kleine dieren hebben weinig lichaamsinhoud en dus een relatief groot huidoppervlak, waardoor ze veel warmte verliezen. Om hun energie goed in balans te houden, moeten ze de hele dag eten. Grotere dieren hebben minder voedsel nodig om warm te blijven. Dus de grote exemplaren van kleine dieren hebben een evolutionair voordeel, waardoor uiteindelijk kleine egels groot worden op een eiland. De reuzenegel was endemisch op Gargano, dat betekent dat het dier nergens anders voorkwam. Tijdens de latere ijstijden daalde de zeespiegel waardoor het eiland aansloot bij het vasteland en de egel uitstierf.

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’.

Je kent hem vast: de dodo! Deze vogel is wereldberoemd omdat hij er niet meer is. Op een eiland ben je kwetsbaar. Zodra er nieuwe dieren voet aan wal zetten, ben je blootgesteld aan gevaar, waar je niet op berekend bent. Als je niet gewend bent aan vijanden kan het snel met je afgelopen zijn. Zo verging het ook de dodo op Mauritius. De dodo was een duifachtige die niet meer kon vliegen. Ook dat is een aanpassing aan het eilandleven: hij had het eenvoudigweg niet meer nodig om het luchtruim te kiezen. Toen in de 16e en 17e eeuw de eerste mensen op het eiland aankwamen, namen ze in hun schepen ratten, apen en varkens mee. Wat er precies gebeurde, is niet bekend. Maar de dodo ging niet op de vlucht en beschermde zijn eieren niet, die dus makkelijk geroofd konden worden. Met de laatste dodo stierf de hele soort uit. Dit was de eerste keer dat door toedoen van de mens een dier uitstierf, vandaar dat de dodo het icoon van uitsterven is geworden.

Naturalis heeft een aantal echte dodobotten in bruikleen van Mauritius.

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.

Naturalis Biodiversity Center
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