HOME

TheInfoList



OR:

The dear enemy effect or dear enemy recognition is an ethological phenomenon in which two neighbouring territorial animals become less aggressive toward one another once territorial borders are well established. As territory owners become accustomed to their neighbours, they expend less time and energy on defensive behaviors directed toward one another. However, aggression toward unfamiliar neighbours remains the same. Some authors have suggested the dear enemy effect is territory residents displaying lower levels of aggression toward familiar neighbours compared to unfamiliar individuals who are non-territorial "floaters".Bee, M.A., (2003). A test of the "dear enemy effect" in the strawberry dart-poison frog (''Dendrobates pumilio''). Behavioral Ecology and Sociobiology, 54: 601-610 The dear enemy effect has been observed in a wide range of animals including mammals, birds, reptiles, amphibians, fish and invertebrates. It can be modulated by factors such as the location of the familiar and unfamiliar animal, the season, and the presence of females. The effect is the converse of the
nasty neighbour effect 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 ani ...
, in which some species are more aggressive towards their neighbours than towards unfamiliar strangers.


Function

The ultimate function of the dear enemy effect is to increase the individual fitness of the animal expressing the behaviour. This increase in fitness is achieved by reducing the time, energy or risk of injury unnecessarily incurred by defending a territory or its resources (e.g. mate, food, space) against a familiar animal with its own territory; the territory-holder already knows about the abilities of the neighbour, and also knows that the neighbour is unlikely to try to take over the territory because it already has one.


Mechanism

The interaction between two neighbours can be modelled as an iterated
prisoner's dilemma The Prisoner's Dilemma is an example of a game analyzed in game theory. It is also a thought experiment that challenges two completely rational agents to a dilemma: cooperate with their partner for mutual reward, or betray their partner ("def ...
game. In this view, a territory owner that acts non-aggressively towards a neighbour can be thought of as cooperating, while a territory owner that acts aggressively towards its neighbour can be considered to have defected. A necessary condition for the prisoner’s dilemma game to hold is that an aggressive individual should enjoy greater benefits than a non-aggressive individual when each is faced with a non-aggressive opponent. This stipulation is plausible, as an aggressive individual might enlarge their territory or steal food or matings from a non-aggressive individual. When cooperation involves a cost, a possible mechanism for achieving stable co-operation is
reciprocal altruism In evolutionary biology, reciprocal altruism is a behaviour whereby an organism acts in a manner that temporarily reduces its fitness while increasing another organism's fitness, with the expectation that the other organism will act in a similar m ...
, where pairs of individuals trade bouts of cooperative behaviour with one another. Dear enemy cooperation could be explained by reciprocal altruism if territorial neighbours use conditional strategies such as
tit for tat Tit for tat is an English saying meaning "equivalent retaliation". It developed from "tip for tap", first recorded in 1558. It is also a highly effective strategy in game theory. An intelligent agent, agent using this strategy will first coope ...
. In the tit-for-tat strategy, a subject will cooperate when its partner (neighbour) cooperates and defect when the partner defects.


Occurrence


In mammals

Territorial
Eurasian beaver The Eurasian beaver (''Castor fiber'') or European beaver is a beaver species that was once widespread in Eurasia, but was hunted to near-extinction for both its fur and castoreum. At the turn of the 20th century, only about 1,200 beavers survi ...
s (''Castor fiber'') presented with a two-way
choice A choice is the range of different things from which a being can choose. The arrival at a choice may incorporate motivators and models. For example, a traveler might choose a route for a journey based on the preference of arriving at a give ...
sniffed both castoreum and anal gland secretion from a stranger longer than from a neighbour. Furthermore, beavers responded aggressively—standing on the mound on their hind feet, pawing, overmarking, or a combination of these—longer to castoreum, but not to anal gland secretion, from a stranger than from a neighbour. When the mounds containing the scents were allowed to remain overnight and the beavers' responses measured the following morning, the beavers' responses were stronger to both castoreum and anal gland secretion from a stranger than from a neighbour.Rosell, F. and Bjørkøyli, T. (2002). A test of the dear enemy phenomenon in the Eurasian beaver. Animal Behaviour, 63: 1073–1078
Eurasian badger The European badger (''Meles meles''), also known as the Eurasian badger, is a badger species in the family Mustelidae native to almost all of Europe. It is classified as least concern on the IUCN Red List as it has a wide range and a large s ...
s (''Meles meles'') can discriminate between self-, neighbour- and unfamiliar- group faeces near their main
sett A sett or set is a badger's den. It usually consists of a network of tunnels and numerous entrances. The largest setts are spacious enough to accommodate 15 or more animals with up to of tunnels and as many as 40 openings. Such elaborate setts ...
. Badgers show heightened behavioural responses towards unfamiliar- compared with self-group scents, but there is no difference in response to neighbour- relative to self-group scents. The relative responses towards unfamiliar-group scents are greatest during the breeding seasons, but there is no seasonal differences in the responses to neighbour-group versus self-group scents. In badger populations, levels of aggression between neighbouring territory-holders are likely to be kept relatively low through neighbour recognition. However, increased levels of aggression will be shown towards dispersing or itinerant (alien) badgers, especially during periods such as the breeding season when the potential threats to the long-term fitness of territory owners are greatest.
Red squirrels The red squirrel (''Sciurus vulgaris'') is a species of tree squirrel in the genus ''Sciurus'' common throughout Europe and Asia. The red squirrel is an arboreal, primarily herbivorous rodent. In Great Britain, Ireland, and in Italy numbers ...
are able to discriminate the odours of familiar neighbours and strangers. It has been suggested that this discrimination may be used by males to avoid unnecessary chases and fights by becoming known to their neighbours.


In birds

Audio playback studies are often used to test the dear enemy effect in birds. These studies have demonstrated several bird species respond more aggressively to played back songs of strangers than to songs of neighbours; such species include the
alder flycatcher The alder flycatcher (''Empidonax alnorum'') is a small insect-eating bird of the tyrant flycatcher family. The genus name ''Empidonax'' is from Ancient Greek ''empis'', " gnat", and ''anax'', "master". The specific ''alnorum'' is Latin and m ...
(''Empidonax alnorum''), male
blue grouse The genus ''Dendragapus'' contains two closely related species of grouse that have often been treated as a single variable taxon (blue grouse). The two species are the dusky grouse (''Dendragapus obscurus'') and the sooty grouse (''Dendragapus ...
,
European robin The European robin (''Erithacus rubecula''), known simply as the robin or robin redbreast in Great Britain & Ireland, is a small insectivorous passerine bird that belongs to the chat subfamily of the Old World flycatcher family. About in len ...
(''Erithacus rubecula''), and male
banded wren The banded wren (''Thryophilus pleurostictus'') is a small songbird of the wren family. It is a resident breeding species from central Mexico to Costa Rica. It was formerly placed in the genus ''Thryothorus'' (Mann et al., 2006). This wren b ...
(''Thryothorus pleurostictus''). Neighbouring male
song sparrow The song sparrow (''Melospiza melodia'') is a medium-sized New World sparrow. Among the native sparrows in North America, it is easily one of the most abundant, variable and adaptable species. Description Adult song sparrows have brown upperp ...
s (''Melodia melospiza'') differ individually in their aggressiveness. Increased aggression by residents towards intruders indicates that residents not only respond to intrinsic aggressiveness of their neighbours, but also to short-term changes in aggression levels.Akçay, C. et al., (2009). Good neighbour, bad neighbour: song sparrows retaliate against aggressive rivals. Animal Behaviour, 78: 97–102 Although neighbour–stranger discrimination has been reported in many
passerine A passerine () is any bird of the order Passeriformes (; from Latin 'sparrow' and '-shaped'), which includes more than half of all bird species. Sometimes known as perching birds, passerines are distinguished from other orders of birds by th ...
birds, it has seldom been investigated in territorial non-passerine species. The nocturnal
raptor Raptor or RAPTOR may refer to: Animals The word "raptor" refers to several groups of bird-like dinosaurs which primarily capture and subdue/kill prey with their talons. * Raptor (bird) or bird of prey, a bird that primarily hunts and feeds on v ...
, the
little owl The little owl (''Athene noctua''), also known as the owl of Athena or owl of Minerva, is a bird that inhabits much of the temperate and warmer parts of Europe, the Palearctic east to Korea, and North Africa. It was introduced into Britain at ...
(''Athene noctua''), hoots to defend its territory. Male little owls respond less to their neighbour's hoots played back from the usual location. However, responses to playback of a neighbour from an unusual location are similar to responses to playback of a stranger's hoots from either location. During the breeding season of the
skylark ''Alauda'' is a genus of larks found across much of Europe, Asia and in the mountains of north Africa, and one of the species (the Raso lark) endemic to the islet of Raso in the Cape Verde Islands. Further, at least two additional species are ...
(''Alauda arvensis''), particular common sequences of syllables (phrases) are produced by all males established in the same location (neighbours), whereas males of different locations (strangers) share only few syllables. Playback experiments provided evidence for neighbour–stranger discrimination consistent with the dear enemy effect, indicating that shared sequences were recognised and identified as markers of the group identity.Briefer, E., Aubin, T., Lehongre, K. and Rybak, F., (2008). How to identify dear enemies: the group signature in the complex song of the skylark ''Alauda arvensis''. Journal of Experimental Biology, 211: 317-326. DOI: 10.1242/jeb.013359 Studies have shown that the dear enemy effect changes during the breeding season of the skylark. Playbacks of neighbour and stranger songs at three periods of the breeding season show that neighbours are dear enemies in the middle of the season, when territories are stable, but not at the beginning of the breeding season, during settlement and pair formation, nor at the end, when bird density increases due to the presence of young birds becoming independent. In song sparrows, where neighbours are most often the sires of extra-pair offspring, males will alter their aggression toward neighbouring males with their female's fertility status. When presented with simulated stranger and neighbour intruders during their female's pre-fertile and post-fertile periods, males displayed the dear enemy effect. However, when presented with simulated stranger and neighbour intruders during their female's fertile period, males exhibited an equal response to both stimuli, likely in order to protect their paternity. Thus, the dear enemy relationship is not a fixed pattern but a flexible one likely to evolve with social and ecological circumstances.


In reptiles

Males of a territorial lizard, the tawny dragon (''
Ctenophorus ''Ctenophorus'' is a genus of lizards, commonly known as comb-bearing dragons, in the family Agamidae. The genus contains the most diverse group of dragon lizards in Australia. It is the largest group of Australian lizards and it has an ex ...
decresii''), reduced their aggression levels in repeat interactions with familiar rivals and increased their aggression levels towards unfamiliar males. The time taken for interactions to be settled was also lower towards familiar than unfamiliar males. Another territorial lizard, the common collared lizard (''Crotaphytus collaris''), can individually recognize neighbours and will increase aggression towards them as the threat to territorial ownership increases. Resident males treat familiar neighbours that had been moved to the opposite boundary to the shared boundary as equally aggressive as strangers. However, residents responded more aggressively towards strangers than towards neighbours on natural territories and also in neutral arena encounters. In the
brown anole The brown anole (''Anolis sagrei''), also known commonly as the Cuban brown anole, or De la Sagra's anole, is a species of lizard in the family Dactyloidae. The species is native to Cuba and the Bahamas. It has been widely introduced elsewhere, ...
lizard (''Anolis sagrei''), dyads of males behave differently depending on whether the lizards are prior neighbours, with prior neighbours exhibiting less bobbing relative to nodding forms of headbob displays than non-neighbours. The Iberian wall lizard (''
Podarcis hispanicus ''Podarcis hispanicus,'' also known as Iberian wall lizard, is a small wall lizard species of the genus ''Podarcis''. It is found in the Iberian peninsula, in northwestern Africa and in coastal districts in Languedoc-Roussillon in France. In Sp ...
'') has been observed to be less aggressive towards conspecifics. It also exhibits headbob activity similar to that of the brown anole.


In amphibians

Males of the territorial breeding
agile frog The agile frog (''Rana dalmatina'') is a European frog in the genus ''Rana'' of the true frog family, Ranidae. Description This species is fat and has long limbs and a pointy snout. Adult males are rarely larger than 6.5 cm, while females ...
(''Rana dalmatina''), have a large variability in call characteristics and are able to discriminate between neighbouring and unfamiliar conspecifics. Calling is of the longest duration in response to an unfamiliar acoustic stimulus; in contrast, the response to a familiar conspecific call does not show any difference from solitary vocalisations. Terrestrial red-backed salamanders, ''Plethodon cinereus'', defend territories under rocks and logs on the forest floor in the eastern United States. Individuals are more aggressive to unfamiliar salamanders than to familiar individuals. In the golden rocket frog, there is variability in the nature of the call and the frog presents a more aggressive call to strangers in comparison to the response to its neighbors.


In fish

The dear enemy effect in male variegated pupfish (''
Cyprinodon ''Cyprinodon'' is a genus of pupfishes found in waters that range from fresh to hypersaline. The genus is primarily found in Mexico, the Caribbean Islands and southern United States (Arizona, California, Florida, Nevada, New Mexico, Oklahoma and ...
variegatus'') is dependent on the presence of females. Reduced aggression consistent with dear enemy recognition occurs between conspecific neighbours in the absence of females, but the presence of a female in a male's territory instigates comparably greater aggression between the neighbours. Some researchers have staged three-way contests between male
convict cichlid The convict cichlid (''Amatitlania nigrofasciata'') is a fish species from the family Cichlidae, native to Central America, also known as the zebra cichlid. Convict cichlids are popular aquarium fish and have also been the subject of numerous stud ...
s (''Cichlasoma nigrofasciatum'') to examine the dear enemy effect. When faced with a familiar neighbour and an unfamiliar intruder simultaneously, residents preferentially confronted the unfamiliar opponent. That is, the establishment of dear enemy recognition between a resident and a neighbour allowed the resident to direct his aggression to the greater competitive threat, i.e. the intruder. Individual recognition of noises produced males of the bicolor damselfish (''Pomacentrus partitus'') have been demonstrated in the field. Playbacks of non-resident sounds from a given fish's territory elicit a greater response from its nearest neighbour than playbacks of the resident's sound. Testing also included switching the sounds of the two nearest neighbours relative to each respective male's territory. Results demonstrated that all males in the colony individually recognize the sounds of their two nearest neighbours.


In invertebrates

The home ranges of colony living ants often overlap the ranges of other conspecific colonies and colonies of other species. In laboratory experiments, the frequency and severity of agonistic interactions among workers from different colonies increases with the distance between their nests; this has been reported for '' Leptothorax nylanderi'' and ''
Pheidole ''Pheidole'' is a genus of ants that belongs to the ant subfamily Myrmicinae. The genus is widespread and ecologically dominant. It probably includes more than 1000 species. The genus first evolved in the Americas, eventually spreading across t ...
'' ants. In the wild, male bees of the species ''
Xylocopa micans ''Xylocopa micans'', also known as the southern carpenter bee, is a species of bee within ''Xylocopa'', the genus of carpenter bees. The southern carpenter bee can be found mainly in the coastal and gulf regions of the southeastern United State ...
'' have been known to slowly fly into the territory of an adjacent male territory holder in order to test and establish the mutual boundary of their two territories. The dear enemy effect has been reported in colonies of the fungus-growing termite ''Macrotermes falciger''. Behavioural tests with workers reveal no alarm behaviour or mortality in pairings of workers from the same colony but a full range from no alarm to overt aggression, with associated death, when individuals were paired from different colonies. The level of mortality increases with differences in the composition of cuticular
hydrocarbons In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ...
between colonies. Male sand fiddler crabs ('' Uca pugilator'') defend territories that consist of a breeding burrow and a display area where they wave their claw to attract females. Burrow-holding males engage in agonistic contests with both intruding males that attempt burrow take-overs and with other territory-holding neighbours that apparently attempt to limit waving or other surface activities of rivals. Contests consist of one or more behavioural elements that range from no claw contact to use of the claw to push, grip, or flip an opponent. In the field, contests with intruders begin at higher intensities and escalate more rapidly than those with neighbours. However, resident–resident contests increase in intensity when burrows are close, neighbours faced each other when exiting burrows, and neighbours were of similar size. Proximity and orientation determine the ease with which a neighbour may be engaged.


Nasty neighbour effect or no effect

A range of studies have found evidence of an effect opposite to the dear enemy effect, i.e. more aggression is shown toward neighbours than strangers. This has been termed the ''nasty neighbour effect''. Colonies of the weaver ant (''Oecophylla smaragdina'') 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 towards neighbours is more common in social species with intense competition between neighbours, as opposed to reduced aggression towards 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. This is opposite to the dear enemy phenomenon and suggests that neighbouring females pose a greater threat than strangers in this species. A range of studies have found no evidence of the dear enemy effect showing the effect is not universal. Territorial males of the
strawberry poison-dart frog The strawberry poison frog, strawberry poison-dart frog or blue jeans poison frog (''Oophaga pumilio'', formerly ''Dendrobates pumilio'') is a species of small poison dart frog found in Central America. It is common throughout its range, which ex ...
(''Dendrobates pumilio'') and the
spotted antbird The spotted antbird (''Hylophylax naevioides'') is a species of bird in the family Thamnophilidae. In southern Central America, it is found in Honduras, Nicaragua, Costa Rica and Panama; also Colombia and Ecuador of northwestern South America. I ...
(''Hylophylax naevioides'') do not discriminate behaviourally between the calls of neighbours and strangers, and female collared lizards show no difference in their behaviour to neighbouring or unfamiliar females.
Guinea baboon The Guinea baboon (''Papio papio'') is a baboon from the Old World monkey family. Some (older) classifications list only two species in the genus ''Papio'', this one and the hamadryas baboon. In those classifications, all other ''Papio'' specie ...
(''Papio papio'') males which live in 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.Maciej, P., Patzelt, A., Ndao, I., Hammerschmidt, K. and Julia Fischer, J., (2013). Social monitoring in a multilevel society: a playback study with male Guinea baboons. Behav. Ecol. Sociobiol., 67(1): 61–68. DOI: 10.1007/s00265-012-1425-1


References

{{Ethology Behavioral ecology Ethology Evolutionary psychology Sociobiology