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Life at stake when playing hide and seek: Concealing effects of prey colouration and visual backgrounds
Stockholm University, Faculty of Science, Department of Zoology.
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

A prey animal can use different strategies to avoid becoming eaten by predators. One such widely recognised strategy is the use of body colouration to decrease the risk of becoming detected, i.e. cryptic colouration. The principles of crypsis that I have studied are background matching, disruptive colouration and distractive markings. Further, I also studied the concealing effect of the visual background habitats. I used artificial prey items and backgrounds, and blue tits (Cyanistes caeruleus) as predators, to investigate prey concealment. In Paper I, I tested if high-contrast markings in prey coloration or in the background would result in a distracting effect. I found that such markings did increase prey search time, even when the prey markings were lighter or darker than the background. In Paper II, I studied the use of chromatic cues by predators when searching for prey. The birds easily detected prey that chromatically deviated from its background. Interestingly, background-matching prey was more difficult to detect when the colour scheme had low ultraviolet and high shortwave reflectance compared to when the reflectance bands were even. In Paper III, I studied optimisation of achromatic contrast within prey colour pattern and also the effect of shape diversity of background pattern elements on prey detection. I found that all prey types were more difficult to detect on the diverse background, but the level of contrast within prey pattern did not influence search times. In Paper IV, I further investigated how a prey should optimise its patterning with respect to background matching. I found that prey with repeated pattern elements was equally hard to detect as prey with more variable pattern. However, prey with a spatially regular pattern (aligned pattern elements) was easier to detect than prey with a spatially irregular pattern. In this paper I also found that high complexity of element shapes in the background, made the search task more difficult.

Place, publisher, year, edition, pages
Stockholm: Department of Zoology, Stockholm University , 2009. , 34 p.
Keyword [en]
predation; adaptive prey coloration; camouflage; concealment; crypsis; background matching; disruptive colouration; distractive markings
National Category
Ecology
Research subject
Animal Ecology
Identifiers
URN: urn:nbn:se:su:diva-30548ISBN: 978-91-7155-959-3 (print)OAI: oai:DiVA.org:su-30548DiVA: diva2:272903
Public defence
2009-11-20, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Manuscript. Paper 2: AcceptedAvailable from: 2009-10-28 Created: 2009-10-18 Last updated: 2009-10-22Bibliographically approved
List of papers
1. Avoiding detection: effects of prey pattern regularity, background matching and complexity of the habitat background
Open this publication in new window or tab >>Avoiding detection: effects of prey pattern regularity, background matching and complexity of the habitat background
(English)Manuscript (preprint) (Other academic)
Abstract [en]

In this study we test how aspects of prey colour pattern regularity affect crypsis and how visual complexity of the background affects prey detection. We performed two predation experiments with artificial prey and backgrounds, using blue tits (Cyanistes caeruleus) as predators. In the first experiment we found that a prey pattern consisting of variable element shapes did not compensate for mismatching pattern elements, because a variable pattern with some mismatching element shapes was easier to detect than a variable pattern with background-matching element shapes only. Contrary to a previous hypothesis, a pattern with regular, background-matching element shapes was not easier to detect than the pattern with variable, background-matching shapes. All prey types were easier to detect on a simple than on a complex background with more diverse and complex element shapes. In the second experiment we used prey pattern consisting of invariable, background-matching elements and tested how spatial regularity of the elements affects crypsis. We found that on a complex background the spatially irregular prey with randomly placed pattern elements was more difficult to detect than the regular prey with all elements aligned, but on a simple background both prey types were equally easy to detect. Here background complexity was due to element shape complexity only. In conclusion, our study shows that spatial regularity of prey pattern but not regularity due to invariable pattern element shapes deteriorates crypsis. Visually complex habitat backgrounds and specifically those consisting of elements with complex shapes make detection of cryptic prey difficult.

National Category
Ecology
Research subject
Animal Ecology
Identifiers
urn:nbn:se:su:diva-30544 (URN)
Available from: 2009-10-18 Created: 2009-10-18 Last updated: 2010-01-14Bibliographically approved
2. Prey concealment: visual background complexity and prey contrast distribution
Open this publication in new window or tab >>Prey concealment: visual background complexity and prey contrast distribution
2010 (English)In: Behavioral Ecology, ISSN 1045-2249, E-ISSN 1465-7279, Vol. 21, no 1, 176-181 p.Article in journal (Refereed) Published
Abstract [en]

A prey may achieve camouflage through background matching and through disruptive coloration. Background matching is based on visual similarity between the prey and its background, whereas disruptive coloration emphasizes the use of highly contrasting pattern elements at the body outline to break up the body shape of the prey. Another factor that may influence prey detection, but has been little studied, is the appearance of the visual characteristics of the background. We taught blue tits (Cyanistes caeruleus) to search for artificial prey and manipulated the appearance of the prey and the background. We studied the effect of diversity of shapes in the background on prey detection time. We also studied the differing predictions from background matching and disruptive coloration with respect to contrast level and location of high-contrast elements in prey patterning. We found that visual background complexity did indeed increase prey detection time. We did not find differences in detection time among prey types. Hence, detection time was not affected by contrast within prey patterning, or whether the prey patterning matched only a sub-sample or all the shades present in the background. Also, we found no effect of the spatial distribution of shades (highest contrast placed marginally or centrally) on detection times. We conclude that background complexity is important for the evolution of prey coloration. We suggest that it may facilitate concealment and favor the evolution of camouflage over warning coloration. Preference for visually complex backgrounds might provide prey with a so far untested means to decrease predation risk.

Keyword
predation; crypsis; camouflage; background matching; disruptive coloration; aposematism
National Category
Ecology
Research subject
Animal Ecology
Identifiers
urn:nbn:se:su:diva-30547 (URN)10.1093/beheco/arp174 (DOI)000272925000025 ()
Available from: 2009-11-30 Created: 2009-10-18 Last updated: 2011-11-23Bibliographically approved
3. Concealed by conspicuousness: distractive prey markings and backgrounds
Open this publication in new window or tab >>Concealed by conspicuousness: distractive prey markings and backgrounds
2009 (English)In: Proceedings of the Royal Society of London. Biological Sciences, ISSN 0962-8452, Vol. 276, no 1163, 1905-1910 p.Article in journal (Refereed) Published
Abstract [en]

High-contrast markings, called distractive or dazzle markings, have been suggested to draw and hold theattention of a viewer, thus hindering detection or recognition of revealing prey characteristics, such asthe body outline.We tested this hypothesis in a predation experiment with blue tits (Cyanistes caeruleus) andartificial prey. We also tested whether this idea can be extrapolated to the background appearanceand whether high-contrast markings in the background would improve prey concealment. We comparedsearch times for a high-contrast range prey (HC-P) and a low-contrast range prey (LC-P) in a high-contrastrange background (HC-B) and a low-contrast range background (LC-B). The HC-P was more difficult todetect in both backgrounds, although it did not match the LC-B. Also, both prey types were more difficultto find in the HC-B than in the LC-B, in spite of the mismatch of the LC-P. In addition, the HC-P wasmore difficult to detect, in both backgrounds, when compared with a generalist prey, not mismatchingeither background. Thus, we conclude that distractive prey pattern markings and selection of microhabitatswith distractive features may provide an effective way to improve camouflage. Importantly, high-contrastmarkings, both as part of the prey coloration and in the background, can indeed increase prey concealment.

Keyword
crypsis; predation; dazzle; disruptive coloration; camouflage; background matching
National Category
Ecology
Research subject
Animal Ecology
Identifiers
urn:nbn:se:su:diva-30546 (URN)10.1098/rspb.2009.0052 (DOI)000264936500021 ()
Available from: 2009-10-18 Created: 2009-10-18 Last updated: 2009-10-19Bibliographically approved
4. Chromaticity in the UV/blue range facilitates the search for achromatically background-matching prey in birds
Open this publication in new window or tab >>Chromaticity in the UV/blue range facilitates the search for achromatically background-matching prey in birds
2009 (English)In: Philosophical Transactions of the Royal Society of London. Biological Sciences, ISSN 0962-8436, Vol. 364, no 1516, 511-517 p.Article in journal (Refereed) Published
Abstract [en]

A large variety of predatory species rely on their visual abilities to locate their prey. However, thesearch for prey may be hampered by prey camouflage. The most prominent example of concealingcoloration is background-matching prey coloration characterized by a strong visual resemblance ofprey to the background. Even though this principle of camouflage was recognized to efficiently workin predator avoidance a long time ago, the underlying mechanisms are not very well known. In thisstudy, we assessed whether blue tits (Cyanistes caeruleus) use chromatic cues in the search for prey.Weused two prey types that were achromatically identical but differed in chromatic properties in theUV/blue range and presented them on two achromatically identical backgrounds. The backgroundshad either the same chromatic properties as the prey items (matching combination) or differed intheir chromatic properties (mismatching combination). Our results show that birds use chromaticcues in the search for mismatching prey, whereupon chromatic contrast leads to a ‘pop-out’ of theprey item from the background. When prey was presented on a matching background, search timeswere significantly higher. Interestingly, search for more chromatic prey on the matching backgroundwas easier than search for less chromatic prey on the matching background. Our results indicate thatbirds use both achromatic and chromatic cues when searching for prey, and that the combination ofboth cues might be helpful in the search task.

Keyword
visual search; crypsis; predation; avian vision; luminance; colour;
National Category
Ecology
Research subject
Animal Ecology
Identifiers
urn:nbn:se:su:diva-30543 (URN)10.1098/rstb.2008.0248 (DOI)000262353500011 ()
Available from: 2009-10-18 Created: 2009-10-18 Last updated: 2009-10-19Bibliographically approved

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