The Post-Diluvian Diaspora is a belief of Young Earth Creationists, and is their effort to explain the distribution of life on earth. After an event such as a Noachian Great Flood, the expected distribution of life would be significantly different than it is today.
Explanation for spread of animals
The events of the Great Flood would kill all land-dwelling life on earth save for a 'seed' population at a single location - the landing point of the ark. The land area today is discontiguous - this presents a problem for the flood account, as there is no apparent means by which animals may migrate to disconnected land.
Creationists have found possible solution to these apparent problems.
A possibility is land bridges, such as the Bering Strait that evolutionists claim led to the colonization of North America.
Land bridges would require that the sea level was, for a time, much lower than is observed today. Given the magnitude of its change during the flood, some 'overshoot' and rebound seems possible.
Accelerated continental drift, or hypertectonics, proposes that all land was for a time connected - a theory similar to the secular geological theory of continental drift and the now-broken continent of Pangaea. While secular geologists date this process occurring over many millions of years, the creationist claim is that it happened over no more than a few hundred or a thousand, possibly due to the lubricating effect of water draining back into the earth following the flood. This model allows animals and humans to repopulate the world while it's connected, prior to the break-up. With the water drained, the rate of drift would slow to the centimeters-per-year observed today.
Some creationists suggest that animals may have been independently recreated following the flood, in a 'second genesis.' This view is criticized as lacking biblical backing.