The Theory of Island Biogeography
Think of a large office building. It can hold many different people, possibly even several different
companies. A smaller office building will hold far fewer people, and may be limited to only one
or two different companies. The limit is due to the amount of space - a larger space can hold more
people and more companies, while a smaller space can't hold as many.
The same idea applies to
. The theory of island biogeography simply says
that a larger island will have a greater number of species than a smaller island. For this theory, an
'island' is any ecosystem that is remarkably different from the surrounding area. So, this could
refer to an actual island in the ocean, or it may be an oasis that is surrounded by a desert.
The theory predicts other things, too. For instance, everything else being equal, distant islands
will have lower immigration rates than those close to a mainland, and equilibrium will occur with
fewer species on distant islands. Close islands will have high immigration rates and support more
species. By similar reasoning, large islands, with their lower extinction rates, will have more
species than small ones -- again everything else being equal (which it frequently is not, for larger
islands often have a greater variety of habitats and more species for that reason).