The study of how biodiversity is spread around the world is known as bio- geography. Mite harvestmen illustrate one of the most common patterns in bio- geography, called vicariance: species become separated from each other when geographical barriers emerge. Those barriers can be formed by oceans, as in the case of the mite harvestmen; they can also be separated by rising mountains, spreading deserts, and shifting rivers. The other major pattern in biogeography, known as dispersal, occurs when species themselves spread away from their place of origin. Birds can fly from one island to another, for example, and insects can float on driftwood. The biogeography of many groups of.
