Facultative symbiosis occurs when:

• A. Species are forced to live together
• B. Species live together out of necessity
• C. Species live together by choice
• D. Species are interdependent for basic needs

Answer: (C)

Facultative symbiosis is characterized by the fact that the organisms involved choose to associate with each other, rather than being forced or entirely dependent on one another for survival. In this type of relationship, the species can exist independently, but they can also benefit from the presence of the other. This means that while these organisms have the option to separate and thrive on their own, they choose to coexist because their interaction offers mutual benefits, such as increased access to resources or enhanced protection.

The idea of choice is central to facultative symbiosis, distinguishing it from other symbiotic relationships that may be more obligate, where the organisms are reliant on each other for survival and reproduction. This flexibility allows the organisms to adapt their associations based on environmental conditions and resource availability.