How does geographical isolation lead to speciation?

• For example, Theres an island with isolated species An earthquake happens, theres now two islands No gene flow, because they both cant swim
• A random mutation on both islands Both island have different selection pressures Selection pressures decide if mutation is advantageous Allele frequency are different on both islands
• Speciation has happened BECAUSE: There are 2 different species of turkeys Cant interbreed with each other Allele frequency changed so much that they evolved into a different species.