Acertain widely distributed mammalian species remained unchanged for about 30 million years. most members of this species lived on a fertile plain, but some members (that were less well adapted) survived in low numbers in the surrounding mountains. they adapted and evolved to this area and became significantly different from their relatives on the plain. a sudden meteorite attack struck the plain and destroyed the plain population. the mountain population was unaffected and as the plain environment recovered moved to the plain. in the absence of competitors, they underwent a very rapid population explosion. which mode of evolution does this example explain