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ethology Ethology is the scientific study of animal behaviour, usually with a focus on behaviour under natural conditions, and viewing behaviour as an evolutionarily adaptive trait. Behaviourism as a term also describes the scientific and object ...
, the nasty neighbour effect describes the phenomenon whereby territory-holding animals behave more strongly toward familiar
conspecific Biological specificity is the tendency of a characteristic such as a behavior or a biochemical variation to occur in a particular species. Biochemist Linus Pauling stated that "Biological specificity is the set of characteristics of living organis ...
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 toward their neighbours than toward unfamiliar strangers. The
four-striped grass mouse The four-striped grass mouse (''Rhabdomys pumilio'') or four-striped grass rat, is a species of rodent in the family Muridae. It is found throughout the southern half of Africa up to above sea level, extending as far north as the Democratic Repu ...
(''
Rhabdomys ''Rhabdomys'' is a largely Southern African genus of muroid rodents slightly larger than house mice. They are known variously as striped or four-striped mice or rats. Traditionally the genus has been seen as a single species, ''Rhabdomys pumilio ...
pumilio'') is group living with one single breeding male and up to four communally breeding females per group. Groups typically contain several
philopatric Philopatry is the tendency of an organism to stay in or habitually return to a particular area. The causes of philopatry are numerous, but natal philopatry, where animals return to their birthplace to breed, may be the most common. The term derive ...
adult sons (and daughters) that are believed not to breed in their natal group and all group members participate in territorial defence. When aggression in wild group-living male breeders was tested in a neutral test arena, they were nearly five times more aggressive toward their neighbours than toward strangers, leading to the prediction that neighbours are the most important competitors for paternity. Using a molecular parentage analysis it was shown that 28% of offspring are sired by neighbouring males and only 7% by strangers. Colonies of the weaver ant (''
Oecophylla smaragdina ''Oecophylla smaragdina'' (common names include Asian weaver ant, weaver ant, green ant, green tree ant, semut rangrang, semut kerangga, and orange gaster) is a species of arboreal ant found in tropical Asia and Australia. These ants form colon ...
'') are able to recognize a greater proportion of workers from neighbouring colonies as non-colony members. When recognized as non-colony members, more aggression is exhibited toward neighbours than non-neighbours.
Banded mongoose The banded mongoose (''Mungos mungo'') is a mongoose species native from the Sahel to Southern Africa. It lives in savannas, open forests and grasslands and feeds primarily on beetles and millipedes. Mongooses use various types of dens for shelt ...
(''Mungos mungo'') groups vocalize more and inspect more scent samples in response to olfactory cues of neighbours than strangers. It has been suggested that increased aggression toward neighbours is more common in social species with intense competition between neighbours, as opposed to reduced aggression toward neighbours typical for most solitary species. Furthermore, animals may respond in this way when encounters with intruders from non-neighbouring colonies are rare and of little consequence. Female
New Zealand bellbird The New Zealand bellbird (''Anthornis melanura''), also known by its Māori names korimako, makomako, and kōmako, is a passerine bird endemic to New Zealand. It has greenish colouration and is the only living member of the genus ''Anthornis''. T ...
s (''Anthornis melanura'') are more aggressive toward the songs of neighbouring females, indicating that neighbouring females pose a greater threat than strangers in this species. Female
hen harrier The hen harrier (''Circus cyaneus'') is a bird of prey. It breeds in Eurasia. The term "hen harrier" refers to its former habit of preying on free-ranging fowl. It migrates to more southerly areas in winter. Eurasian birds move to southern Eur ...
(''Circus cyaneus'') responses toward neighbours are more intense, mostly flights rather than calls, than responses toward female floaters (individuals without territories), which in turn were more intense than responses toward male floaters.


No effect

Guinea baboon (''Papio papio'') males which live in social groups called "gangs" do not differ in their response behaviour toward neighbouring and stranger males, and largely ignore any non-gang member, irrespective of familiarity; that is, they neither show a "dear enemy" nor "nasty neighbour" effect.


References

{{Ethology Ethology Behavioral ecology