We start with the rabbit population. This rabbit populations variation is fur color. Some rabbits have brown and some have white.
A flash flood hits and seperates the rabbits. On one side is a more wintery biome, with lots of now and on the other is a more green vegataton biome.
On the more wintery biome the white rabbits survive because they are able to blend in and avoid predation better. This causes the brown rabbits to slowly die off over many generations and the white rabbits to because more common.
On the other side of the new formed river though, the brown rabbits are surviv9ng with their brown fur that helps them blend into their environment. The white rabbits struggle to survive with the heavy predation on this side.
Eventually over many many generations and hundreds of years the brown rabbits and white rabbits are different species.
Finally after a very long time the two new species meet. They are unable to interbreed and produce healthy, fertile offspring because their DNA is so different. Speciation has occurred.