in ethology, the nasty neighbour effect describes the phenomenon whereby territory-holding animals behave more strongly toward familiar conspecific neighbours than to unfamiliar conspecifics. this phenomenon may be generally advantageous to an animal because the heightened response reduces the likelihood of a nearby intruder entering the territory and taking the resources it contains whereas an unfamiliar or distant territory-holder poses less of a threat. this reduced response minimises the time, energy and risk of injury incurred during territorial encounters with animals which are less of a threat to the territory holder. the nasty neighbour effect is the converse of the dear enemy effect in which some species are less aggressive towards their neighbours than towards unfamiliar strangers.