Many dogs bark when unknown individuals approach their house. what type of interaction is this

It's competition.

Explanation:

This kind of interaction is called competition. Competition is defined as an interaction between organisms or species in which both the organisms or species are harmed, the limitation of one resource (water, food, territory) could be a factor for this competition. Dogs bark at intruders warning them that they'll have to attack if they try to take their resources.

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