Predatory imminence continuum: Difference between revisions
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[[Animalia|Animals]] have many different tactics for defending themselves, depending on the severity of the threat they are encountering.<ref>{{cite journal | last1 = Bolles | first1 = RCF | last2 = Fanselow | first2 = MS | year = 1980 | title = A perceptual-defensive-recuperative model of fear and pain | url = | journal = Behav Brain Sci | volume = 3 | issue = | pages = 291–301 | doi=10.1017/s0140525x0000491x}}</ref> Stages of threat vary along a [[spectrum]] referred to as the "predatory imminence continuum," spanning from low-risk (pre-encounter) to high-risk (interaction) threats.<ref>Blanchard DC, Blanchard RJ (1969) Passive and active reactions to fear-eliciting stimuli. J Comp Physiol Psychol 68:129-135.</ref><ref name=":0">Fanselow MS, Lester LS (1988) A functional behavioristic approach to aversively motivated behavior: Predatory imminence as a determinant of the topography of defensive behavior. In Evolution and Learning. Bolles RC, Beecher MD, Eds,; Earlbaum, Hillsdale NJ:185-211.</ref> The main assumption of the '''predatory imminence continuum''' is that as threat levels increase, defensive response strategies change. During the pre-encounter period, an animal may engage in activities like exploration or foraging. But if the animal senses that a [[predator]] is nearby, the animal may begin to express [[Neuroethology|species specific defense reactions]] such as freezing<ref>Blanchard DC, Blanchard RJ (1969) Crouching as an index of fear. J Comp Physiol Psychol 67:370-375.</ref><ref name=":1">{{Cite journal|last=Bolles|first=Robert C.|title=Species-specific defense reactions and avoidance learning. |
[[Animalia|Animals]] have many different tactics for defending themselves, depending on the severity of the threat they are encountering.<ref>{{cite journal | last1 = Bolles | first1 = RCF | last2 = Fanselow | first2 = MS | year = 1980 | title = A perceptual-defensive-recuperative model of fear and pain | url = | journal = Behav Brain Sci | volume = 3 | issue = 2| pages = 291–301 | doi=10.1017/s0140525x0000491x}}</ref> Stages of threat vary along a [[spectrum]] referred to as the "predatory imminence continuum," spanning from low-risk (pre-encounter) to high-risk (interaction) threats.<ref>Blanchard DC, Blanchard RJ (1969) Passive and active reactions to fear-eliciting stimuli. J Comp Physiol Psychol 68:129-135.</ref><ref name=":0">Fanselow MS, Lester LS (1988) A functional behavioristic approach to aversively motivated behavior: Predatory imminence as a determinant of the topography of defensive behavior. In Evolution and Learning. Bolles RC, Beecher MD, Eds,; Earlbaum, Hillsdale NJ:185-211.</ref> The main assumption of the '''predatory imminence continuum''' is that as threat levels increase, defensive response strategies change. During the pre-encounter period, an animal may engage in activities like exploration or foraging. But if the animal senses that a [[predator]] is nearby, the animal may begin to express [[Neuroethology|species specific defense reactions]] such as freezing<ref>Blanchard DC, Blanchard RJ (1969) Crouching as an index of fear. J Comp Physiol Psychol 67:370-375.</ref><ref name=":1">{{Cite journal|last=Bolles|first=Robert C.|title=Species-specific defense reactions and avoidance learning.|journal=Psychological Review|volume=77|issue=1|pages=32–48|doi=10.1037/h0028589|year=1970}}</ref> in an attempt to [[Crypsis|avoid detection]] by the predator. However, in situations where a threat is imminent, once the animal is detected by its predator, freezing may no longer be the optimal behaviour for survival. At this point, the animal enters the [[Fight-or-flight response|circa-strike phase]], where its behaviour will transition from passive freezing to active flight, or even attack if escape is not possible.<ref name=":0" /> |
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== Development of the predatory imminence continuum == |
== Development of the predatory imminence continuum == |
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The development of the predatory imminence continuum began with the description of species-specific defence reactions.<ref name=":1" /><ref name=":2">{{Cite journal|last=Fanselow|first=Michael S.|date=1994-12-01|title=Neural organization of the defensive behavior system responsible for fear |
The development of the predatory imminence continuum began with the description of species-specific defence reactions.<ref name=":1" /><ref name=":2">{{Cite journal|last=Fanselow|first=Michael S.|date=1994-12-01|title=Neural organization of the defensive behavior system responsible for fear|journal=Psychonomic Bulletin & Review|language=en|volume=1|issue=4|pages=429–438|doi=10.3758/bf03210947|pmid=24203551|issn=1069-9384}}</ref> Species-specific defence reactions are innate responses demonstrated by an animal when they experience a threat.<ref name=":1" /> Since survival behaviours are so vital for an animal to acquire and demonstrate rapidly, it has been theorized that these defence reactions would not have time to be learned and therefore, must be innate.<ref name=":1" /> While these behaviours are species-specific, there are three general categories of defence reactions - fleeing, freezing, and threatening.<ref name=":1" /><ref name=":2" /><ref name=":3">{{Cite journal|last=Fanselow|first=Michael|last2=Sigmundi|first2=Ronald|last3=Williams|first3=Jon|date=1987|title=Response Selection and the Hierarchical Organization of Species-Specific Defense Reactions: The Relationship Between Freezing, Flight, and Defensive Burying|url=https://search.proquest.com/openview/f163074f8b84d02b0019a6d700683081/1?pq-origsite=gscholar&cbl=1817765|journal=The Psychological Record|volume=37|pages=381–386|via=}}</ref> Species-specific defence reactions are now recognized as being organized in a hierarchical system where different behaviours are exhibited, depending on the level of threat experienced.<ref name=":0" /><ref name=":2" /> However, when this concept was first proposed, the dominant species-specific defence reaction in a certain context was thought to be controlled by operant conditioning.<ref name=":1" /> That is, if a species-specific defence reaction was unsuccessful in evading or controlling conflict, the hierarchical system would be rearranged because of the punishment, in the form of failure, experienced by an animal.<ref name=":1" /> It would then be unlikely for that species-specific defence reaction to be used in a similar situation again; instead, an alternative behaviour would be dominant.<ref name=":1" /> However, if the dominant behaviour was successful it would remain the recurring behaviour for that situation.<ref name=":1" /> After experimentation, this theory was met with much opposition, even by the person who proposed it.<ref name=":0" /><ref name=":3" /><ref name=":4">{{Cite journal|last=Bolles|first=Robert C.|last2=Riley|first2=Anthony L.|title=Freezing as an avoidance response: Another look at the operant-respondent distinction|url=http://linkinghub.elsevier.com/retrieve/pii/0023969073900167|journal=Learning and Motivation|volume=4|issue=3|pages=268–275|doi=10.1016/0023-9690(73)90016-7|year=1973}}</ref> One point of opposition was found through the use of shock on rats and the species-specific defence reaction of freezing.<ref name=":4" /> This experiment found that while punishment did seem to affect freezing, it was not through response weakening but through the evoking of different levels of the behaviour.<ref name=":4" /> Other criticisms for this theory focused on the inability for species-specific defence reactions to effectively rearrange in this manner in natural situations.<ref name=":3" /> It has been argued that there would not be enough time for punishment, in the form of an animal being unsuccessful in its defence, to reorder the hierarchy of species-specific defence reactions.<ref name=":3" /> The rejection of the operant conditioning mechanism for the reorganization of species-specific defence reactions, led to the development of the predatory imminence continuum. The organization of defensive behaviours can be attributed to the level of threat an animal perceives itself to be in.<ref name=":0" /><ref name=":2" /> This theory is one of adaptiveness, as the dominant defence reaction is the behaviour which is most effective in allowing the survival of the animal and the one which is most effective in preventing an increasing level of threat, also known as increasing imminence.<ref name=":0" /> The probability of being killed by a predator, known as predatory imminence, is what is responsible for the expressed defensive behaviour.<ref name=":0" /> The predatory imminence is dependent on many factors such as the distance from a predator, the potential for escape, and the likelihood of meeting a predator.<ref name=":0" /> Three general categories of defensive behaviours, based on increasing predatory imminence, have been identified.<ref name=":0" /> These are labelled as pre-encounter, post-encounter, and circa-strike defensive behaviours.<ref name=":0" /> |
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== Stages of threat == |
== Stages of threat == |
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=== Pre-encounter === |
=== Pre-encounter === |
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Behaviours exhibited by animals when the threat of a predator is extremely low are known as preferred activity patterns.<ref name=":0" /> When the likelihood of predation increases above this point an animal enters into pre-encounter defensive behaviours.<ref name=":0" /> These behaviours are used to reduce the probability of having to exhibit avoidance behaviours, which are evoked when a predator is detected.<ref name=":0" /> Pre-encounter behaviours can be observed when an animal has left the safety of its residence to perform tasks such as mating or foraging, and occur before a predator has been identified.<ref name=":0" /><ref>{{Cite journal|last=Kitaoka|first=A.|title=Defensive aspects of burrowing behavior in rats (Rattus Norvegicus): A descriptive and correlational study|url=http://linkinghub.elsevier.com/retrieve/pii/0376635794900345|journal=Behavioural Processes|volume=31|issue=1|pages=13–27|doi=10.1016/0376-6357(94)90034-5|year=1994}}</ref> The animal does not perform these behaviours because of a predator, instead these behaviours are performed or altered depending on the probability of being detected by a predator when executing a task.<ref name=":0" /> One well studied example of a pre-encounter behaviour is that of varying meal frequency and size seen in foraging rats.<ref name=":0" /><ref name=":5">{{Cite journal|last=Fanselow|first=M. S.|last2=Lester|first2=L. S.|last3=Helmstetter|first3=F. J.|date=November 1988|title=Changes in feeding and foraging patterns as an antipredator defensive strategy: a laboratory simulation using aversive stimulation in a closed economy|journal=Journal of the Experimental Analysis of Behavior|volume=50|issue=3|pages=361–374|doi=10.1901/jeab.1988.50-361|issn=0022-5002|pmc=1338904|pmid=3209954}}</ref><ref name=":6">{{Cite journal|last=Helmstetter|first=Fred J.|last2=Fanselow|first2=Michael S.|date=1993-06-01|title=Aversively motivated changes in meal patterns of rats in a closed economy: The effects of shock density |
Behaviours exhibited by animals when the threat of a predator is extremely low are known as preferred activity patterns.<ref name=":0" /> When the likelihood of predation increases above this point an animal enters into pre-encounter defensive behaviours.<ref name=":0" /> These behaviours are used to reduce the probability of having to exhibit avoidance behaviours, which are evoked when a predator is detected.<ref name=":0" /> Pre-encounter behaviours can be observed when an animal has left the safety of its residence to perform tasks such as mating or foraging, and occur before a predator has been identified.<ref name=":0" /><ref>{{Cite journal|last=Kitaoka|first=A.|title=Defensive aspects of burrowing behavior in rats (Rattus Norvegicus): A descriptive and correlational study|url=http://linkinghub.elsevier.com/retrieve/pii/0376635794900345|journal=Behavioural Processes|volume=31|issue=1|pages=13–27|doi=10.1016/0376-6357(94)90034-5|year=1994}}</ref> The animal does not perform these behaviours because of a predator, instead these behaviours are performed or altered depending on the probability of being detected by a predator when executing a task.<ref name=":0" /> One well studied example of a pre-encounter behaviour is that of varying meal frequency and size seen in foraging rats.<ref name=":0" /><ref name=":5">{{Cite journal|last=Fanselow|first=M. S.|last2=Lester|first2=L. S.|last3=Helmstetter|first3=F. J.|date=November 1988|title=Changes in feeding and foraging patterns as an antipredator defensive strategy: a laboratory simulation using aversive stimulation in a closed economy|journal=Journal of the Experimental Analysis of Behavior|volume=50|issue=3|pages=361–374|doi=10.1901/jeab.1988.50-361|issn=0022-5002|pmc=1338904|pmid=3209954}}</ref><ref name=":6">{{Cite journal|last=Helmstetter|first=Fred J.|last2=Fanselow|first2=Michael S.|date=1993-06-01|title=Aversively motivated changes in meal patterns of rats in a closed economy: The effects of shock density|journal=Animal Learning & Behavior|language=en|volume=21|issue=2|pages=168–175|doi=10.3758/bf03213397|issn=0090-4996}}</ref> When rats forage they do not typically hoard food, instead they either ingest the food where it was found or retreat to a nearby safe space to consume their meal.<ref>{{Cite journal|last=Whishaw|first=Ian|last2=Gorny|first2=Borguslaw|date=1991|title=The defensive strategies of foraging rats: A review and synthesis|url=http://web.a.ebscohost.com/ehost/detail/detail?vid=0&sid=f872974c-e5fe-4c2e-af52-6b0400cb78f2%40sessionmgr4007&bdata=JkF1dGhUeXBlPWlwLHVybCx1aWQmc2l0ZT1laG9zdC1saXZlJnNjb3BlPXNpdGU%3d#db=bth&AN=9609040798|journal=Psychological Review|volume=41|issue=2|pages=185–205|via=|doi=10.1007/bf03395105}}</ref> Depending on the level of perceived threat, a rat will vary the frequency of foraging and the size of its meal.<ref name=":0" /><ref name=":5" /><ref name=":6" /> In laboratory studies investigating this pre-encounter behaviour, density of shocks are often used to represent the risk of predation.<ref name=":0" /><ref name=":5" /><ref name=":6" /> A number of shocks are administered daily on a random schedule, the more shocks administered per day the higher the perceived predatory imminence.<ref name=":0" /><ref name=":5" /><ref name=":6" /> The shocks only affect the rats when they are outside of their safe nest area, but to get food they have to leave this area and press a lever to dispense their meal.<ref name=":0" /><ref name=":5" /><ref name=":6" /> This models the real-life situation of a rat needing to leave the relative safety of its nest to go foraging for food.<ref name=":0" /><ref name=":5" /><ref name=":6" /> The common finding is that, as the perceived threat of predation increases, the frequency of foraging decreases but the size of the consumed meal increases.<ref name=":0" /><ref name=":5" /><ref name=":6" /> The increased meal size ensures that even though the rat leaves the safe area in search of food less often, it still consumes a relatively constant amount of food each day, regardless of shock density.<ref name=":0" /> This organized modulation of foraging behaviour is consistent with a pre-encounter defensive behaviour. The frequency and meal size associated with foraging are reorganized depending on the perceived level of threat but they are not directly influenced by the interaction with a predator.<ref name=":0" /> |
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=== Post-encounter === |
=== Post-encounter === |
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Post-encounter defensive behaviours are avoidance behaviours performed when a predator is present and has been detected.<ref name=":0" /> When this stage of threat has been reached, behaviours are limited to species-specific defence reactions.<ref name=":0" /> These behaviours are commonly freezing, fleeing or threatening.<ref name=":1" /> The goal of a post-encounter defensive behaviour is to prevent the predatory imminence from further increasing.<ref name=":0" /> The dominant post-encounter defensive behaviour can depend on whether the predator has also detected the prey and how far away the two animals are from one another.<ref name=":0" /><ref name=":7">{{Cite journal|last=Kawai|first=Nobuyuki|last2=Kono|first2=Reiko|last3=Sugimoto|first3=Sanae|title=Avoidance learning in the crayfish (Procambarus clarkii) depends on the predatory imminence of the unconditioned stimulus: a behavior systems approach to learning in invertebrates|url=http://linkinghub.elsevier.com/retrieve/pii/S0166432803002614|journal=Behavioural Brain Research|volume=150|issue=1–2|pages=229–237|doi=10.1016/s0166-4328(03)00261-4|year=2004}}</ref> Varying levels of predatory imminence, even in post-encounter situations, can affect the expressed defensive behaviour.<ref name=":7" /> If the prey has yet to be detected, the goal of the post-encounter behaviour will be to prevent the predator from detecting the prey.<ref name=":0" /> If both the predator and prey have detected each other, the goal will be to avoid making contact with the predator.<ref name=":0" /> Freezing behaviour in rats is an example of a post-encounter defensive behaviour which has been well studied.<ref name=":0" /><ref name=":8">{{Cite journal|last=Bouton|first=Mark E.|last2=Bolles|first2=Robert C.|date=1980-09-01|title=Conditioned fear assessed by freezing and by the suppression of three different baselines |
Post-encounter defensive behaviours are avoidance behaviours performed when a predator is present and has been detected.<ref name=":0" /> When this stage of threat has been reached, behaviours are limited to species-specific defence reactions.<ref name=":0" /> These behaviours are commonly freezing, fleeing or threatening.<ref name=":1" /> The goal of a post-encounter defensive behaviour is to prevent the predatory imminence from further increasing.<ref name=":0" /> The dominant post-encounter defensive behaviour can depend on whether the predator has also detected the prey and how far away the two animals are from one another.<ref name=":0" /><ref name=":7">{{Cite journal|last=Kawai|first=Nobuyuki|last2=Kono|first2=Reiko|last3=Sugimoto|first3=Sanae|title=Avoidance learning in the crayfish (Procambarus clarkii) depends on the predatory imminence of the unconditioned stimulus: a behavior systems approach to learning in invertebrates|url=http://linkinghub.elsevier.com/retrieve/pii/S0166432803002614|journal=Behavioural Brain Research|volume=150|issue=1–2|pages=229–237|doi=10.1016/s0166-4328(03)00261-4|year=2004}}</ref> Varying levels of predatory imminence, even in post-encounter situations, can affect the expressed defensive behaviour.<ref name=":7" /> If the prey has yet to be detected, the goal of the post-encounter behaviour will be to prevent the predator from detecting the prey.<ref name=":0" /> If both the predator and prey have detected each other, the goal will be to avoid making contact with the predator.<ref name=":0" /> Freezing behaviour in rats is an example of a post-encounter defensive behaviour which has been well studied.<ref name=":0" /><ref name=":8">{{Cite journal|last=Bouton|first=Mark E.|last2=Bolles|first2=Robert C.|date=1980-09-01|title=Conditioned fear assessed by freezing and by the suppression of three different baselines|journal=Animal Learning & Behavior|language=en|volume=8|issue=3|pages=429–434|doi=10.3758/bf03199629|issn=0090-4996}}</ref> Freezing in rats is characterized by sudden, extended immobility, followed by a decreased heart rate and an increased respiration rate.<ref>{{Cite journal|last=Hofer|first=M. A.|date=November 1970|title=Cardiac and respiratory function during sudden prolonged immobility in wild rodents|journal=Psychosomatic Medicine|volume=32|issue=6|pages=633–647|issn=0033-3174|pmid=5530023|doi=10.1097/00006842-197011000-00008}}</ref> This behaviour is often the dominant post-encounter defence behaviour in rats.<ref name=":0" /> In the laboratory setting, post-encounter defensive behaviours can be elicited by pairing a neutral stimulus, such as a light, with an aversive stimulus, such as a shock.<ref name=":0" /><ref name=":8" /> The rat will engage in its post-encounter defensive behaviour when it becomes aware of the neutral stimulus, as the stimulus is acting as a predictor for the shock.<ref name=":0" /><ref name=":8" /> Since the freezing behaviour is dominant in these situations, it can be assumed that it serves an adaptive function by preventing an additional increase in predatory imminence.<ref name=":0" /> Freezing is the dominant post-encounter behaviour because even when there are alternative defensive reactions available, freezing has been observed to be the rat's response the majority of the time.<ref name=":0" /> Even when a clear method of escape was made available, rats would freeze instead of fleeing.<ref name=":0" /> Freezing can prevent the perceived level of threat from increasing in several ways.<ref name=":9">{{Cite journal|last=Suarez|first=Susan D.|last2=Gallup|first2=Gordon G.|title=An ethological analysis of open-field behavior in rats and mice|url=http://linkinghub.elsevier.com/retrieve/pii/0023969081900138|journal=Learning and Motivation|volume=12|issue=3|pages=342–363|doi=10.1016/0023-9690(81)90013-8|year=1981}}</ref> If a rat becomes aware of a predator before the predator is aware of the prey, freezing can reduce the likelihood that the prey will be detected.<ref name=":9" /> As well, since many predators rely on motion to keep track of their prey, freezing may cause the predator to either lose site of their prey or shift their attention to a more active object.<ref name=":9" /> |
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=== Circa-strike === |
=== Circa-strike === |
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When a predator is prepared to strike or has stricken, the prey's behaviours change from post-encounter to circa-strike defensive behaviours.<ref name=":0" /> These reactions are employed if the post-encounter behaviours are unsuccessful.<ref name=":0" /> A predator making contact with its prey is the highest level of predatory imminence experienced before being killed by a predator.<ref name=":0" /> Therefore, the goal of circa-strike behaviours are to survive and escape from the predator during or after contact.<ref name=":0" /> These defence behaviours are often more reactive than post-encounter behaviours and are commonly in the form of jumping, vocalizing, striking or biting.<ref name=":0" /> If the animal is successful in evading its predator then, when it has found a safe location, it will eventually return to its preferred activity patterns.<ref name=":0" /> One example of an extremely successful circa-strike defensive behaviour is the evasive leaping of the kangaroo rat.<ref name=":10">{{Cite journal|last=Whitford|first=Malachi D.|last2=Freymiller|first2=Grace A.|last3=Clark|first3=Rulon W.|title=Avoiding the serpent's tooth: predator–prey interactions between free-ranging sidewinder rattlesnakes and desert kangaroo rats|url=http://linkinghub.elsevier.com/retrieve/pii/S0003347217301793|journal=Animal Behaviour|volume=130|pages=73–78|doi=10.1016/j.anbehav.2017.06.004|year=2017}}</ref> Kangaroo rats are desert dwelling mammals preyed upon by venomous sidewinder rattlesnakes.<ref name=":10" /><ref name=":11">{{Cite journal|last=Randall|first=Jan A.|last2=Hatch|first2=Susan M.|last3=Hekkala|first3=Evon R.|date=1995-04-01|title=Inter-specific variation in anti-predator behavior in sympatric species of kangaroo rat |
When a predator is prepared to strike or has stricken, the prey's behaviours change from post-encounter to circa-strike defensive behaviours.<ref name=":0" /> These reactions are employed if the post-encounter behaviours are unsuccessful.<ref name=":0" /> A predator making contact with its prey is the highest level of predatory imminence experienced before being killed by a predator.<ref name=":0" /> Therefore, the goal of circa-strike behaviours are to survive and escape from the predator during or after contact.<ref name=":0" /> These defence behaviours are often more reactive than post-encounter behaviours and are commonly in the form of jumping, vocalizing, striking or biting.<ref name=":0" /> If the animal is successful in evading its predator then, when it has found a safe location, it will eventually return to its preferred activity patterns.<ref name=":0" /> One example of an extremely successful circa-strike defensive behaviour is the evasive leaping of the kangaroo rat.<ref name=":10">{{Cite journal|last=Whitford|first=Malachi D.|last2=Freymiller|first2=Grace A.|last3=Clark|first3=Rulon W.|title=Avoiding the serpent's tooth: predator–prey interactions between free-ranging sidewinder rattlesnakes and desert kangaroo rats|url=http://linkinghub.elsevier.com/retrieve/pii/S0003347217301793|journal=Animal Behaviour|volume=130|pages=73–78|doi=10.1016/j.anbehav.2017.06.004|year=2017}}</ref> Kangaroo rats are desert dwelling mammals preyed upon by venomous sidewinder rattlesnakes.<ref name=":10" /><ref name=":11">{{Cite journal|last=Randall|first=Jan A.|last2=Hatch|first2=Susan M.|last3=Hekkala|first3=Evon R.|date=1995-04-01|title=Inter-specific variation in anti-predator behavior in sympatric species of kangaroo rat|journal=Behavioral Ecology and Sociobiology|language=en|volume=36|issue=4|pages=243–250|doi=10.1007/bf00165833|issn=0340-5443}}</ref> When rattlesnakes strike, kangaroo rats exhibit a quick and forceful circa-strike behaviour in the form of a leap using their hind legs.<ref name=":10" /><ref name=":11" /> This leaping reaction serves several functions both to help escape and prevent envenomation.<ref name=":10" /><ref name=":11" /> First, the kangaroo rat is able to jump within around 50ms after perceiving an incoming snake strike.<ref name=":10" /> This gives the rat the ability to avoid contact with the predator all together, thus allowing it to escape unharmed.<ref name=":10" /><ref name=":11" /> If the leap is unsuccessful in completely avoiding the snake's strike, it still serves the purpose of preventing the fangs from embedding.<ref name=":10" /> The jumping action is so forceful that the rat may be able to disrupt the snake's striking movement.<ref name=":10" /> Finally, if all else fails and the fangs have made contact with the kangaroo rat, it is still able to employ its evasive leaping behaviour, and with the use of its hind legs, forcefully dislodge the snake's fangs and prevent envenomation.<ref name=":10" /> This leaping behaviour serves the function of preventing or escaping contact with a predator immediately before, during, or after an attack, therefore, it is consistent with a circa-strike defensive behaviour.<ref name=":0" /><ref name=":10" /><ref name=":11" /> |
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==References== |
==References== |
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Revision as of 02:50, 6 February 2019
Animals have many different tactics for defending themselves, depending on the severity of the threat they are encountering.[1] Stages of threat vary along a spectrum referred to as the "predatory imminence continuum," spanning from low-risk (pre-encounter) to high-risk (interaction) threats.[2][3] The main assumption of the predatory imminence continuum is that as threat levels increase, defensive response strategies change. During the pre-encounter period, an animal may engage in activities like exploration or foraging. But if the animal senses that a predator is nearby, the animal may begin to express species specific defense reactions such as freezing[4][5] in an attempt to avoid detection by the predator. However, in situations where a threat is imminent, once the animal is detected by its predator, freezing may no longer be the optimal behaviour for survival. At this point, the animal enters the circa-strike phase, where its behaviour will transition from passive freezing to active flight, or even attack if escape is not possible.[3]
Development of the predatory imminence continuum
The development of the predatory imminence continuum began with the description of species-specific defence reactions.[5][6] Species-specific defence reactions are innate responses demonstrated by an animal when they experience a threat.[5] Since survival behaviours are so vital for an animal to acquire and demonstrate rapidly, it has been theorized that these defence reactions would not have time to be learned and therefore, must be innate.[5] While these behaviours are species-specific, there are three general categories of defence reactions - fleeing, freezing, and threatening.[5][6][7] Species-specific defence reactions are now recognized as being organized in a hierarchical system where different behaviours are exhibited, depending on the level of threat experienced.[3][6] However, when this concept was first proposed, the dominant species-specific defence reaction in a certain context was thought to be controlled by operant conditioning.[5] That is, if a species-specific defence reaction was unsuccessful in evading or controlling conflict, the hierarchical system would be rearranged because of the punishment, in the form of failure, experienced by an animal.[5] It would then be unlikely for that species-specific defence reaction to be used in a similar situation again; instead, an alternative behaviour would be dominant.[5] However, if the dominant behaviour was successful it would remain the recurring behaviour for that situation.[5] After experimentation, this theory was met with much opposition, even by the person who proposed it.[3][7][8] One point of opposition was found through the use of shock on rats and the species-specific defence reaction of freezing.[8] This experiment found that while punishment did seem to affect freezing, it was not through response weakening but through the evoking of different levels of the behaviour.[8] Other criticisms for this theory focused on the inability for species-specific defence reactions to effectively rearrange in this manner in natural situations.[7] It has been argued that there would not be enough time for punishment, in the form of an animal being unsuccessful in its defence, to reorder the hierarchy of species-specific defence reactions.[7] The rejection of the operant conditioning mechanism for the reorganization of species-specific defence reactions, led to the development of the predatory imminence continuum. The organization of defensive behaviours can be attributed to the level of threat an animal perceives itself to be in.[3][6] This theory is one of adaptiveness, as the dominant defence reaction is the behaviour which is most effective in allowing the survival of the animal and the one which is most effective in preventing an increasing level of threat, also known as increasing imminence.[3] The probability of being killed by a predator, known as predatory imminence, is what is responsible for the expressed defensive behaviour.[3] The predatory imminence is dependent on many factors such as the distance from a predator, the potential for escape, and the likelihood of meeting a predator.[3] Three general categories of defensive behaviours, based on increasing predatory imminence, have been identified.[3] These are labelled as pre-encounter, post-encounter, and circa-strike defensive behaviours.[3]
Stages of threat
Pre-encounter
Behaviours exhibited by animals when the threat of a predator is extremely low are known as preferred activity patterns.[3] When the likelihood of predation increases above this point an animal enters into pre-encounter defensive behaviours.[3] These behaviours are used to reduce the probability of having to exhibit avoidance behaviours, which are evoked when a predator is detected.[3] Pre-encounter behaviours can be observed when an animal has left the safety of its residence to perform tasks such as mating or foraging, and occur before a predator has been identified.[3][9] The animal does not perform these behaviours because of a predator, instead these behaviours are performed or altered depending on the probability of being detected by a predator when executing a task.[3] One well studied example of a pre-encounter behaviour is that of varying meal frequency and size seen in foraging rats.[3][10][11] When rats forage they do not typically hoard food, instead they either ingest the food where it was found or retreat to a nearby safe space to consume their meal.[12] Depending on the level of perceived threat, a rat will vary the frequency of foraging and the size of its meal.[3][10][11] In laboratory studies investigating this pre-encounter behaviour, density of shocks are often used to represent the risk of predation.[3][10][11] A number of shocks are administered daily on a random schedule, the more shocks administered per day the higher the perceived predatory imminence.[3][10][11] The shocks only affect the rats when they are outside of their safe nest area, but to get food they have to leave this area and press a lever to dispense their meal.[3][10][11] This models the real-life situation of a rat needing to leave the relative safety of its nest to go foraging for food.[3][10][11] The common finding is that, as the perceived threat of predation increases, the frequency of foraging decreases but the size of the consumed meal increases.[3][10][11] The increased meal size ensures that even though the rat leaves the safe area in search of food less often, it still consumes a relatively constant amount of food each day, regardless of shock density.[3] This organized modulation of foraging behaviour is consistent with a pre-encounter defensive behaviour. The frequency and meal size associated with foraging are reorganized depending on the perceived level of threat but they are not directly influenced by the interaction with a predator.[3]
Post-encounter
Post-encounter defensive behaviours are avoidance behaviours performed when a predator is present and has been detected.[3] When this stage of threat has been reached, behaviours are limited to species-specific defence reactions.[3] These behaviours are commonly freezing, fleeing or threatening.[5] The goal of a post-encounter defensive behaviour is to prevent the predatory imminence from further increasing.[3] The dominant post-encounter defensive behaviour can depend on whether the predator has also detected the prey and how far away the two animals are from one another.[3][13] Varying levels of predatory imminence, even in post-encounter situations, can affect the expressed defensive behaviour.[13] If the prey has yet to be detected, the goal of the post-encounter behaviour will be to prevent the predator from detecting the prey.[3] If both the predator and prey have detected each other, the goal will be to avoid making contact with the predator.[3] Freezing behaviour in rats is an example of a post-encounter defensive behaviour which has been well studied.[3][14] Freezing in rats is characterized by sudden, extended immobility, followed by a decreased heart rate and an increased respiration rate.[15] This behaviour is often the dominant post-encounter defence behaviour in rats.[3] In the laboratory setting, post-encounter defensive behaviours can be elicited by pairing a neutral stimulus, such as a light, with an aversive stimulus, such as a shock.[3][14] The rat will engage in its post-encounter defensive behaviour when it becomes aware of the neutral stimulus, as the stimulus is acting as a predictor for the shock.[3][14] Since the freezing behaviour is dominant in these situations, it can be assumed that it serves an adaptive function by preventing an additional increase in predatory imminence.[3] Freezing is the dominant post-encounter behaviour because even when there are alternative defensive reactions available, freezing has been observed to be the rat's response the majority of the time.[3] Even when a clear method of escape was made available, rats would freeze instead of fleeing.[3] Freezing can prevent the perceived level of threat from increasing in several ways.[16] If a rat becomes aware of a predator before the predator is aware of the prey, freezing can reduce the likelihood that the prey will be detected.[16] As well, since many predators rely on motion to keep track of their prey, freezing may cause the predator to either lose site of their prey or shift their attention to a more active object.[16]
Circa-strike
When a predator is prepared to strike or has stricken, the prey's behaviours change from post-encounter to circa-strike defensive behaviours.[3] These reactions are employed if the post-encounter behaviours are unsuccessful.[3] A predator making contact with its prey is the highest level of predatory imminence experienced before being killed by a predator.[3] Therefore, the goal of circa-strike behaviours are to survive and escape from the predator during or after contact.[3] These defence behaviours are often more reactive than post-encounter behaviours and are commonly in the form of jumping, vocalizing, striking or biting.[3] If the animal is successful in evading its predator then, when it has found a safe location, it will eventually return to its preferred activity patterns.[3] One example of an extremely successful circa-strike defensive behaviour is the evasive leaping of the kangaroo rat.[17] Kangaroo rats are desert dwelling mammals preyed upon by venomous sidewinder rattlesnakes.[17][18] When rattlesnakes strike, kangaroo rats exhibit a quick and forceful circa-strike behaviour in the form of a leap using their hind legs.[17][18] This leaping reaction serves several functions both to help escape and prevent envenomation.[17][18] First, the kangaroo rat is able to jump within around 50ms after perceiving an incoming snake strike.[17] This gives the rat the ability to avoid contact with the predator all together, thus allowing it to escape unharmed.[17][18] If the leap is unsuccessful in completely avoiding the snake's strike, it still serves the purpose of preventing the fangs from embedding.[17] The jumping action is so forceful that the rat may be able to disrupt the snake's striking movement.[17] Finally, if all else fails and the fangs have made contact with the kangaroo rat, it is still able to employ its evasive leaping behaviour, and with the use of its hind legs, forcefully dislodge the snake's fangs and prevent envenomation.[17] This leaping behaviour serves the function of preventing or escaping contact with a predator immediately before, during, or after an attack, therefore, it is consistent with a circa-strike defensive behaviour.[3][17][18]
References
- ^ Bolles, RCF; Fanselow, MS (1980). "A perceptual-defensive-recuperative model of fear and pain". Behav Brain Sci. 3 (2): 291–301. doi:10.1017/s0140525x0000491x.
- ^ Blanchard DC, Blanchard RJ (1969) Passive and active reactions to fear-eliciting stimuli. J Comp Physiol Psychol 68:129-135.
- ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag ah ai aj ak al am an ao ap aq ar Fanselow MS, Lester LS (1988) A functional behavioristic approach to aversively motivated behavior: Predatory imminence as a determinant of the topography of defensive behavior. In Evolution and Learning. Bolles RC, Beecher MD, Eds,; Earlbaum, Hillsdale NJ:185-211.
- ^ Blanchard DC, Blanchard RJ (1969) Crouching as an index of fear. J Comp Physiol Psychol 67:370-375.
- ^ a b c d e f g h i j Bolles, Robert C. (1970). "Species-specific defense reactions and avoidance learning". Psychological Review. 77 (1): 32–48. doi:10.1037/h0028589.
- ^ a b c d Fanselow, Michael S. (1994-12-01). "Neural organization of the defensive behavior system responsible for fear". Psychonomic Bulletin & Review. 1 (4): 429–438. doi:10.3758/bf03210947. ISSN 1069-9384. PMID 24203551.
- ^ a b c d Fanselow, Michael; Sigmundi, Ronald; Williams, Jon (1987). "Response Selection and the Hierarchical Organization of Species-Specific Defense Reactions: The Relationship Between Freezing, Flight, and Defensive Burying". The Psychological Record. 37: 381–386.
- ^ a b c Bolles, Robert C.; Riley, Anthony L. (1973). "Freezing as an avoidance response: Another look at the operant-respondent distinction". Learning and Motivation. 4 (3): 268–275. doi:10.1016/0023-9690(73)90016-7.
- ^ Kitaoka, A. (1994). "Defensive aspects of burrowing behavior in rats (Rattus Norvegicus): A descriptive and correlational study". Behavioural Processes. 31 (1): 13–27. doi:10.1016/0376-6357(94)90034-5.
- ^ a b c d e f g Fanselow, M. S.; Lester, L. S.; Helmstetter, F. J. (November 1988). "Changes in feeding and foraging patterns as an antipredator defensive strategy: a laboratory simulation using aversive stimulation in a closed economy". Journal of the Experimental Analysis of Behavior. 50 (3): 361–374. doi:10.1901/jeab.1988.50-361. ISSN 0022-5002. PMC 1338904. PMID 3209954.
- ^ a b c d e f g Helmstetter, Fred J.; Fanselow, Michael S. (1993-06-01). "Aversively motivated changes in meal patterns of rats in a closed economy: The effects of shock density". Animal Learning & Behavior. 21 (2): 168–175. doi:10.3758/bf03213397. ISSN 0090-4996.
- ^ Whishaw, Ian; Gorny, Borguslaw (1991). "The defensive strategies of foraging rats: A review and synthesis". Psychological Review. 41 (2): 185–205. doi:10.1007/bf03395105.
- ^ a b Kawai, Nobuyuki; Kono, Reiko; Sugimoto, Sanae (2004). "Avoidance learning in the crayfish (Procambarus clarkii) depends on the predatory imminence of the unconditioned stimulus: a behavior systems approach to learning in invertebrates". Behavioural Brain Research. 150 (1–2): 229–237. doi:10.1016/s0166-4328(03)00261-4.
- ^ a b c Bouton, Mark E.; Bolles, Robert C. (1980-09-01). "Conditioned fear assessed by freezing and by the suppression of three different baselines". Animal Learning & Behavior. 8 (3): 429–434. doi:10.3758/bf03199629. ISSN 0090-4996.
- ^ Hofer, M. A. (November 1970). "Cardiac and respiratory function during sudden prolonged immobility in wild rodents". Psychosomatic Medicine. 32 (6): 633–647. doi:10.1097/00006842-197011000-00008. ISSN 0033-3174. PMID 5530023.
- ^ a b c Suarez, Susan D.; Gallup, Gordon G. (1981). "An ethological analysis of open-field behavior in rats and mice". Learning and Motivation. 12 (3): 342–363. doi:10.1016/0023-9690(81)90013-8.
- ^ a b c d e f g h i j Whitford, Malachi D.; Freymiller, Grace A.; Clark, Rulon W. (2017). "Avoiding the serpent's tooth: predator–prey interactions between free-ranging sidewinder rattlesnakes and desert kangaroo rats". Animal Behaviour. 130: 73–78. doi:10.1016/j.anbehav.2017.06.004.
- ^ a b c d e Randall, Jan A.; Hatch, Susan M.; Hekkala, Evon R. (1995-04-01). "Inter-specific variation in anti-predator behavior in sympatric species of kangaroo rat". Behavioral Ecology and Sociobiology. 36 (4): 243–250. doi:10.1007/bf00165833. ISSN 0340-5443.