# 8.3: Summary of interactions

- Page ID
- 25466

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In summary, based on the effects of each population on the other, two species can interact mainly in three different ways, as shown in Figure \(\PageIndex{1}\). Competition is a ‘−−’ combination, mutualism is ‘++’, and predation is ‘+−’, in either order.

Sandwiched between the boxes above are special cases where one of the interaction terms is zero, or very close to zero. These are called “commensalism,” when one parameter is positive and the other is zero, or “amensalism,” when one parameter is negative and the other is zero. We won’t focus further on these special cases.