In ecology, what is the difference between dispersal and vicariance?

Question

In ecology, what is the difference between dispersal and vicariance?

Answer 1

dispersal is the movement or expansion of a species into a new area.  

vicariance is the separation of species by a geographical barrier.  eg- formation of amtn range, or rising sea levels creat islands

they dont sound all that similar but there is large argument on the cause of historical speciation about whether one or the other took place.

1. vicariance - species existed - then were separated and underwent allopatric speciation.,

2. dispersal - species disperses across an EXISTING barrier- eg. islands already exist - some individuals made it to the next island, underwent allopatric speciation.