Final answer:
Speciation within a single undivided population is known as sympatric speciation, where reproductive barriers arise without geographic separation, unlike allopatric speciation, which involves physical barriers.
Step-by-step explanation:
Speciation within a single undivided population occurs through a process called sympatric speciation. This type of speciation does not require geographical barriers to isolate populations; instead, it can result from genetic changes that create reproductive barriers within the population, such as polyploidy, behavioral changes, or ecological niches.
In contrast, allopatric speciation occurs when a population is divided by a physical barrier, leading to geographical isolation and eventually genetic divergence. An example of allopatric speciation is the case of the different species of squirrels found on opposite sides of the Grand Canyon.
Both sympatric and allopatric speciation are mechanisms that lead to the formation of new species by creating reproductive isolation between groups within a population or between geographically separated populations, respectively.