Dear enemy effect

===In mammals===

===In mammals===

[[File:Badger-badger.jpg|right|thumb|Eurasian badgers respond less aggressively to the scent of familiar conspecifics than unfamiliar]]

[[File:Badger-badger.jpg|right|thumb|Eurasian badgers respond less aggressively to the scent of familiar conspecifics than unfamiliar.]]

Territorial [[Eurasian beaver]]s (''Castor fiber'') presented with a two-way [[Preference tests (animals)|choice]] 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

Territorial [[Eurasian beaver]]s (''Castor fiber'') presented with a two-way [[Preference tests (animals)|choice]] 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

===In birds===

===In birds===

[[File:Mochuelo Común ( Athene noctua )(1).jpg|thumb|right|upright|The little owl hoots less intensively at familiar neighbours than unfamiliar]]

[[File:Mochuelo Común ( Athene noctua )(1).jpg|thumb|right|upright|The little owl hoots less intensively at familiar neighbours than unfamiliar.]]

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]] (''Empidonax alnorum''),Lovell, S.F. (2004). Neighbor-stranger discrimination by song in a suboscine bird, the alder flycatcher, ''Empidonax alnorum''. Behavioral Ecology, 15: 799-804 DOI: 10.1093/beheco/arh082 male [[Dendragapus|blue grouse]],Falls, J.B. and McNicholl, M.K., (1979). Neighbor-stranger discrimination by song in male blue grouse. Canadian Journal of Zoology, 57: 457-462 [[European robin]] (''Erithacus rubecula''),Brindley, E.L., (1991). Response of European robins to playback of song: neighbor recognition and overlapping. Animal Behaviour, 41: 503-512 and male [[banded wren]] (''Thryothorus pleurostictus'').Mollesf, L.E. and Vehrencamp, S.L., (2001). Neighbour recognition by resident males in the banded wren, Thryothorus pleurostictus, a tropical songbird with high song type sharing. Animal Behaviour, 61: 119–127

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]] (''Empidonax alnorum''),Lovell, S.F. (2004). Neighbor-stranger discrimination by song in a suboscine bird, the alder flycatcher, ''Empidonax alnorum''. Behavioral Ecology, 15: 799-804 DOI: 10.1093/beheco/arh082 male [[Dendragapus|blue grouse]],Falls, J.B. and McNicholl, M.K., (1979). Neighbor-stranger discrimination by song in male blue grouse. Canadian Journal of Zoology, 57: 457-462 [[European robin]] (''Erithacus rubecula''),Brindley, E.L., (1991). Response of European robins to playback of song: neighbor recognition and overlapping. Animal Behaviour, 41: 503-512 and male [[banded wren]] (''Thryothorus pleurostictus'').Mollesf, L.E. and Vehrencamp, S.L., (2001). Neighbour recognition by resident males in the banded wren, Thryothorus pleurostictus, a tropical songbird with high song type sharing. Animal Behaviour, 61: 119–127

The dear enemy effect has been reported in colonies of the fungus-growing termite [[Macrotermitinae|''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 [[Cuticle|cuticular]] [[hydrocarbons]] between colonies.Kaib1, M., Franke, S., Francke, W. and Brand, R., (2002). Cuticular hydrocarbons in a termite: phenotypes and a neighbour–stranger effect. Physiological Entomology, 27, 189–198. DOI: 10.1046/j.1365-3032.2002.00292.x

The dear enemy effect has been reported in colonies of the fungus-growing termite [[Macrotermitinae|''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 [[Cuticle|cuticular]] [[hydrocarbons]] between colonies.Kaib1, M., Franke, S., Francke, W. and Brand, R., (2002). Cuticular hydrocarbons in a termite: phenotypes and a neighbour–stranger effect. Physiological Entomology, 27, 189–198. DOI: 10.1046/j.1365-3032.2002.00292.x

[[File:Crabby Fiddler - Flickr - Andrea Westmoreland.jpg|thumb|right|Male sand fiddler crabs attract mates by waving]]The dear enemy effect has been documented in several species of fiddler crabs including sand fiddler crabs (''[[Uca pugilator]]'') and banana fiddler crabs (''[[Austruca mjoebergi]]''){{Cite journal |last=Booksmythe |first=Isobel |last2=Jennions |first2=Michael D. |last3=Backwell |first3=Patricia R. Y. |date=2010-02-01 |title=Investigating the ‘dear enemy’ phenomenon in the territory defence of the fiddler crab, Uca mjoebergi |url=https://www.sciencedirect.com/science/article/pii/S0003347209005259 |journal=Animal Behaviour |volume=79 |issue=2 |pages=419–423 |doi=10.1016/j.anbehav.2009.11.020 |issn=0003-3472}}. In these species males 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.Pratt, A.E. and McLain, D.K., (2006). How dear is my enemy: Intruder-resident and resident-resident encounters in male sand fiddler crabs (Uca pugilator). Behaviour, 143: 597-617

[[File:Crabby Fiddler - Flickr - Andrea Westmoreland.jpg|thumb|right|Male sand fiddler crabs attract mates by waving.]]The dear enemy effect has been documented in several species of fiddler crabs including sand fiddler crabs (''[[Uca pugilator]]'') and banana fiddler crabs (''[[Austruca mjoebergi]]''){{Cite journal |last=Booksmythe |first=Isobel |last2=Jennions |first2=Michael D. |last3=Backwell |first3=Patricia R. Y. |date=2010-02-01 |title=Investigating the ‘dear enemy’ phenomenon in the territory defence of the fiddler crab, Uca mjoebergi |url=https://www.sciencedirect.com/science/article/pii/S0003347209005259 |journal=Animal Behaviour |volume=79 |issue=2 |pages=419–423 |doi=10.1016/j.anbehav.2009.11.020 |issn=0003-3472}}. In these species males 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.Pratt, A.E. and McLain, D.K., (2006). How dear is my enemy: Intruder-resident and resident-resident encounters in male sand fiddler crabs (Uca pugilator). Behaviour, 143: 597-617

==Nasty neighbour effect or no effect==

==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''.

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''.

[[File:Strawberry poison dart frog (70539).jpg|thumb|[[Strawberry poison-dart frog]]]]

[[File:Strawberry poison dart frog (70539).jpg|thumb|[[Strawberry poison dart frog]]]]

{{Listen|filename=Oophaga_pumilio_call.ogg|left|title=Listen to the strawberry dart-poison frog|description=Male advertisement call|format=[[Ogg]]}}

{{Listen|filename=Oophaga_pumilio_call.ogg|left|title=Listen to the strawberry dart-poison frog|description=Male advertisement call|format=[[Ogg]]}}

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.Newey, P.S., Robson, S.K. and Crozier, R.H., (2010). Weaver ants Oecophylla smaragdina encounter nasty neighbors rather than dear enemies. Ecology, 91(8):2366-72 [[Banded mongoose]] (''Mungos mungo'') groups vocalize more and inspect more scent samples in response to olfactory cues of neighbours than strangers.Müller, C.A. and Manser, M.B., (2007). ‘Nasty neighbours’ rather than ‘dear enemies’ in a social carnivore. Proc. R. Soc. B., 274: 959-965 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.

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.Newey, P.S., Robson, S.K. and Crozier, R.H., (2010). Weaver ants Oecophylla smaragdina encounter nasty neighbors rather than dear enemies. Ecology, 91(8):2366-72 [[Banded mongoose]] (''Mungos mungo'') groups vocalize more and inspect more scent samples in response to olfactory cues of neighbours than strangers.Müller, C.A. and Manser, M.B., (2007). ‘Nasty neighbours’ rather than ‘dear enemies’ in a social carnivore. Proc. R. Soc. B., 274: 959-965 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.