Final answer:
A species is a group of metapopulations that diverge due to isolation and evolution through natural selection, a process known as allopatric speciation. Population variation affects the distribution of phenotypes, and geographic isolation can lead to the formation of new species.
Step-by-step explanation:
A species is a collection of metapopulations in a geographic region that has evolved one or more characteristics distinguishing it from other metapopulations due to isolation and subsequent divergence resulting from natural selection. This process is known as allopatric speciation, where the separation and subsequent evolution of populations lead to the formation of distinct species. In such scenarios, each metapopulation may be subject to different selection pressures, environmental conditions, or genetic drift, which can lead to the populations becoming increasingly different in their allele frequencies. These genetic differences can accumulate to a point where the populations can no longer interbreed, and thus, a new species is formed.
Population variation is another term that refers to the distribution of phenotypes within a population and can be affected by local environmental pressures. Isolation, such as in the case of geographic barriers or habitat changes, can reinforce these variations resulting in increased differentiation. Ultimately, the evolution of unique species in geographically isolated areas underscores how physical separation can lead to significant evolutionary change.