If we assign a '+' sign to represent beneficial interactions, a '-' sign to represent detrimental interactions, and a '0' sign to represent neutral interactions, then the population interaction represented by a '+' '-' refers to what?

Parasitism

The correct answer is Option (4) - Parasitism

In parasitism, one species (the parasite) benefits from the interaction, while the other species (the host) is harmed. This is represented by the + and - signs, respectively.

Mutualism is a type of interaction in which both species benefit.

Commensalism is a type of interaction in which one species benefits, while the other species is neither harmed nor benefited.

Amensalism is a type of interaction in which one species is harmed, while the other species is unaffected.

Therefore, the population interaction represented by (+) (-) refers to parasitism.