Step 1: Understanding the Concept:
The question asks to identify population interactions with a (+/-) relationship, where one species benefits (+) and the other is harmed (-).
Step 3: Detailed Explanation:
Let's analyze the interactions:
\[\begin{array}{rl} \bullet & \text{(A) Competition (-/-): Both species are harmed as they compete for the same limited resources.} \\ \bullet & \text{(B) Parasitism (+/-): The parasite benefits by deriving nutrients from the host, which is harmed in the process.} \\ \bullet & \text{(C) Amensalism (-/0): One species is harmed while the other is unaffected. For example, a large tree shading a small plant.} \\ \bullet & \text{(D) Predation (+/-): The predator benefits by capturing and consuming the prey, which is harmed (killed).} \\ \end{array}\]
Based on this analysis, Parasitism and Predation are the two interactions where one species benefits and the other is harmed.
Step 4: Final Answer:
The correct interactions are (B) Parasitism and (D) Predation only.