Since the populations were separated and were not able to interact, they could not reproduce. Eventually, mutations would work their ways into each of the separate populations of squirrels. Since the two populations can't mix their genes through breeding they will slowly start to get different. For example, one population could experience a mutation that changes the color of one animals in the one of the populations. This squirrel will spread its genes to its offspring and if it is a good trait then it will spread throughout the population. The other population will not experience a widespread invasion of this trait because the two populations can't breed.
Carrying capacity is the maximum number of individuals of one species that a particular environment can support. Limiting factors determine this number.
