Which of the following is an example of a physical barrier that can lead to speciation?

A physical barrier that can lead to speciation refers to a geographical feature that separates populations, preventing them from interbreeding. The formation of a river is a classic example of such a barrier. When a river forms, it can divide a population of organisms into two distinct groups. Over time, each group can experience different environmental pressures, mutations, and evolutionary changes, leading to genetic divergence and potentially resulting in the emergence of new species.

In contrast, the establishment of a breeding season does not involve a physical separation but rather a behavioral change that can influence mating patterns within the same population. The emergence of new food sources may lead to changes in behavior or diet but does not physically separate populations. Changes in population size can impact genetic diversity and survival rates, but they do not constitute a barrier that prevents interaction and reproduction between separate groups. Thus, the formation of a river effectively illustrates how a physical barrier can initiate the speciation process.