Final answer:
In a hybrid zone, hybrids can compete and reproduce, potentially resulting in scenarios like speciation reinforcement, fusion, or stability. Reinforcement is more likely when hybrids are less fit than the parent species. If hybrids are as fit or fitter than parents, fusion can occur.
Step-by-step explanation:
In a hybrid zone, the hybrids themselves could compete and reproduce. Reinforcement in the hybrid zone is more likely to occur if the hybrids are less fit than their parents, leading to a process where the two species further diverge until they cannot mate and produce viable offspring. This process is known as speciation reinforcement. If, however, the hybrid offspring are as fit or more fit than their parents, it's possible that the two species may fuse back into one species. When both scenarios of reinforcement and fusion are not observed, and two species continue to interact and produce some hybrids without significant changes in their status, this is described as stability in the hybrid zone.