Several ecology students were tracking the population ranges of two species of squirrels that live in the Cascade Range of Oregon. These students noted that when both species of squirrels were present in a region, species A could be found from sea level to about 900 feet above sea level, and species B could be found from about 900 feet to 1,500 feet above sea level. However, when species B was found alone, it had a range of about 500 feet to 1,500 feet above sea level. This is an example of ________.

According to the principle of competitive exclusion, the two species, which compete for the exact identical resources cannot coexist stably. Of these two competitors, one will always exhibit a slight advantage over the other, which results in the extinction of the second competitor in the prolonged time.

It can also result in an evolutionary shift of the inferior competitor towards a distinct ecological niche. As an outcome, the competing associated species usually evolve differentiating features in the regions where they both coexist. This helps in mate identification, thus, sustaining the superiority of each species in exploiting somewhat distinct ecological niches.