Blackwell Publishing

Evolutionary biogeography - What factors limit the geographic range of a species?


Historical factors

There are patterns in the distribution of species that probably cannot be explained by ecological factors alone. For example, historical factors may have been at work.

• There may be places where a species ecologically could be present, but it is absent because it has never arrived - that is, never migrated and established itself. The grey squirrel for instance has never reached islands off the British mainland and consequently red squirrels can still be found on them.

• Suppose that a species is equally well adapted to the physical conditions of two places, but is present in one but absent from the other. We then find that it is excluded by an ecological competitor from one place but not the other. The distribution could then be determined by the historical accident of which of the two competitors established itself in a place first.

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