Final answer:
The competition coefficient of zero (a12=0) between a probiotic and a pathogen indicates that the probiotic does not affect the pathogen's population dynamics, suggesting no competition between them.
Step-by-step explanation:
When considering the competition coefficient between two species, such as a probiotic and a pathogen, a value of a12=0 indicates that the presence of the probiotic does not affect the pathogen's ability to survive and reproduce. Thus, the correct answer to the student's question is option 3: no, because if a12=0, the pathogen is not affected by the probiotic population.
It is a misunderstanding to assume that simply because two organisms share the same environment, they are in competition with each other. The competitive exclusion principle states that no two species can occupy the same niche in the same environment for a long time, which includes competition for resources. However, a competition coefficient of zero contradicts this expectation, as it means one species' population size does not influence the other's. This is in line with the concept of competitive exclusion and interspecific competition, which refer to the process where one organism outcompetes another for resources, leading to the exclusion of the less competitive species.
The question touches on basic biological interactions in ecosystems, specifically within the context of the human microbiome. With probiotics and pathogens playing significant roles in human health, understanding these interactions is crucial for advancing knowledge in microbiology and medicine.