Question

which of these must occur for speciation to happen?
reproductive isolation
temporal isolation
behavioral isolation
geographic isolation

Explanation:

Speciation is the formation of new species. Reproductive isolation is essential as it prevents gene flow between populations, allowing them to diverge genetically until they become distinct species. Temporal, behavioral, and geographic isolations are types of pre - reproductive isolation mechanisms, but reproductive isolation (the broader concept) is the key requirement for speciation.

Answer:

reproductive isolation