When two species draw on the same limiting nutrient, each reduces the amount available to the other. Both populations consequently experience lower growth, survival, or reproduction than they would in the other's absence, producing the (-,-) outcome of interspecific competition. Competitive effects can occur through exploitation of a shared resource or through direct interference, and their strength depends on resource supply, uptake traits, and niche overlap. Mutualism benefits both species, amensalism harms one while leaving the other unaffected, and parasitism benefits one at the other's ex
Ref:
Ecology: From Individuals to Ecosystems, Begon et al., 5th Ed., Ch. 8-13