I was just wondering how, when a landmass has become isolated from another by natural processes, speciation and not extinction would await a lone pair of, say, monkeys who arrived there by rafting.  Surely two or a few animals drifting onto the landmass would not be able to survive, far less procreate?  And just how much of an influence on biodiversity do such events have?

Hi Anthony,

Another good question that generally speaking we know very little about.

We do know that animals have made such journeys, survived and managed to produce a viable population at the other end - based on divergence times for species compared with divergence times for landmasses. Some volcanic islands (e.g. Hawaii) were never connected to a major continent and yet support a range of species that have close relatives living on nearby continents.

Although it does seem unlikely that a single breeding pair could be responsible for this. (There is an inbreeding problem (something that is well known to ramp up the number of deleterious (bad) genes - not to mention the fact that most animals are naturally averse to mating with a sibling).

Most biologists I've chatted to about this will talk in vague terms of storm events that will send a large mass of vegetation (presumably with various critters clinging on for dear life) off across the sea, eventually winding up on some island, but as far as I'm aware there are no reliable recordings of such events.

On the other hand, it would only take one such event to populate an island with a broad range of new animals and when a population is smaller chance variations (known as genetic drift) have a greater chance of producing a new species.

As to the effect on biodiversity islands very often do contain many endemic species (species that are unique to just one place) and hence do tend to increase global biodiversity.