Final answer:
B. commensalism; herbivore, The trophic facilitation phenomenon described by Hacker and colleagues involves a commensalism relationship between two plant species, with indirect effects benefiting a herbivore.
Step-by-step explanation:
A commensalism relationship occurs when one species benefits from a close prolonged interaction, while the other species is unaffected. The correct answer is B. In the trophic facilitation phenomenon described by Hacker and colleagues, the direct interaction between two plant species is commensalism. One plant species benefits from the interaction, while the other is neither benefited nor harmed. In this case, the indirect effects of the commensalism benefit a herbivore, which is a consumer that feeds on plants. Therefore, the correct answer is B. commensalism; herbivore.