Temporal isolation primarily occurs when:

Temporal isolation occurs when two populations breed at different times, which prevents them from interbreeding even if they coexist in the same habitat. This difference in timing can be related to various factors such as seasonal changes, time of day, or even specific years in a predictable cycle. For example, if one species breeds in the spring while another breeds in late summer, the two populations will not have the opportunity to mate, leading to reproductive isolation.

This mechanism is an important factor in the process of speciation, as it allows for the divergence of species without geographic separation. Over time, as these populations remain separate, they can accumulate genetic differences that may eventually lead to the formation of new species.

In contrast, geographic barriers separate populations physically, which relates to geographic isolation rather than temporal isolation. Other options refer to different forms of reproductive isolation mechanisms, such as behavioral differences or speciation occurring in the same geographic area, which do not specifically address the timing aspect crucial to temporal isolation.