Parasitism benefits the parasite through food, habitat, or transmission opportunities while imposing a fitness cost on the host, so its standard sign pattern is (+,-) when the parasite is listed first. Host costs may include tissue damage, nutrient loss, impaired reproduction, altered behavior, or increased mortality. Unlike a parasitoid, a parasite does not necessarily kill the host as a required developmental outcome, because prolonged host survival can support continued exploitation. (+,0) denotes commensalism and (0,0) neutrality. The reversed notation (-,+) could describe the same relatio
Ref:
Ecology: From Individuals to Ecosystems, Begon et al., 5th Ed., Ch. 8-13