Saturday, August 31, 2013

Island living

Madagascar is the world’s fourth largest island. It is thought to have reached its present day location in relation to the African continent about 130 million years ago. Today, 400km separate Madagascar from the rest of Africa. Lemuriformes are though to have colonized Madagascar roughly around 65 million years ago, so how did the ancestors of sifakas, ring-tailed lemurs, and others arrive on the island? Are lemurs great endurance swimmers? Not exactly.

Madagascar's hissing cockroaches
What determines whether a species colonizes an island? Is colonization of an island something scientists can predict? The principles of island biogeography lend us a hand in determining whether or not an island will be successfully colonized by new species.

For starters, the closer the island is to the mainland or another large land mass, the more likely that island is to be colonized. The older the island is the more likely the island is to be colonized. The larger the island is the more species are likely to colonize it. All of these fancy rules are pretty simple once you think about them. The older the island is, the more time has passed, allowing species to reach the island. The larger the island is, the more space there is for all of those new species. And the closer the island is to other landmasses, the less distance between the two landmasses makes for an easier crossing for new species.

In terms of the genetics behind island biogeography, the following rules apply. As time passes and the island has been settled by those species that were able to the island and been successfully live there, genes are less likely to be exchanged between the original population from the mainland and the population on the island. As even more time passes, the two populations become genetically different.

Ancestral lemurs likely reached Madagascar by a series of rafts. This would have occurred not over a summer holiday but over an extended period of time in a series of events. As time passed, ancestral lemurs diverged from their original population and became genetically distinct. They thrived on the island of Madagascar and became the species we know today.

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