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Mark Elgar
Animal Behaviour
Correlation, experimentationand comparison
1
Outline
How do researchers make discoveries about animal behaviour?Natural variation
Experiments
Comparisons between species
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Why do animals forage in groups?
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Predator vigilanceProb
ability*of*
detec/on
*
Group*size*
Probability of predator detection increases with group size
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Predator vigilanceScan
ning'
rate'
Group'size'
Rate of scanning declines with increasing group size
4
Predator vigilance
Use natural variation in flock size to measure differences in scanning rate
Flock size
Head
-jerk
rate
/min
0
5
10
15
20
25
2 4 6 8 10 13 18 23 28 33 50
5
Studies of group foraging
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The dilution effect
Probability = 1
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The dilution effect
Probability = 1Probability = 1/2
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The dilution effect
Probability = 1Probability = 1/2Probability = 1/3
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The dilution effect
Probability = 1Probability = 1/2Probability = 1/3Probability = 1/10
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The dilution effect
Individuals may invest less in scanning when risk of predation is lower
Are individuals changing their scanning rate due to the Dilution Effect, the
detection of predators or both?
?
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Patchy distributions
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Experimental approaches
Feeder1
Feeder2
Feeder3
Feeder4
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Experimental approaches
7"6"5"4"3"2"1"0"0"
4"
8"
12"
16"
20"
Flock&size&
Scan
s&pe
r&min&"
Negative correlation between scanning rate and flock size
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Selfish Herd Effect
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Experimental approaches
Long
feeder
VS
Square feeder
Spotted turtle doveSpilopelia chinensis
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10#8#6#4#2#0#0.0#
0.1#
0.2#
0.3#
0.4#
0.5#
Flock#size#
Vigilance#
Square#Feeder#Narrow#Feeder#
Experimental approaches
Birds reduced scanning rate with increasing
group size
Scanning rate was also lower at the square
feeder
Results:
Spotted turtle doveSpilopelia chinensis
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Do all birds forage in groups?
Large group size may lower predation risk, but also means increased competition for foodPredicition:
Foraging in groups less common in populations or
species where predation risk is low or non-existent
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Comparative analyses
Comparison of island versus mainland species of birds
Island species typically have smaller flock sizes than mainland species
Island Mainland
Mean flock size
Maximum flock size
Smaller Larger
Smaller Larger
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Ways of studying behavior (relying on natural variation; field experiments; inter-specific comparative analyses
Summary
Experiments reveal that individuals can reduce the risk of predation by foraging in groups, although comparative analyses suggest that other factors may promote group foraging.
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Cita%onsSlide-1 _MG_2581(peacock(spider(Maratus(volans(by(Jurgen(O=o((h=p://www.flickr.com/photos/59431731@N05/5521738809/).((Reproduced(with(permission(from(Jurgen(O=o.
Slide-3a)("Bison(herd(R(Lake(Audy(R(Riding(Mountain(NaUonal(Park"((h=p://commons.wikimedia.org/wiki/File%3ABison_herd_R_Lake_Audy_R_Riding_Mountain_NaUonal_Park.JPG)(by(Norm(Andreiw((CC(BY(3.0),(via(Wikimedia(Commonsb)("Shorebirds(01"((h=p://commons.wikimedia.org/wiki/File%3AShorebirds_01.jpg)(by(Ingrid(Taylar((CC(BY(2.0),(via(Wikimedia(Commonsc)( "Starfish(orgy((SUchaster(australis)"((h=p://commons.wikimedia.org/wiki/File%3AStarfish_orgy_%28SUchaster_australis%29.jpg)(by("Avenue"((CC(BYRSA(3.0),(via(Wikimedia(Commonsd)("Cassiopea(jellyfish"((h=p://commons.wikimedia.org/wiki/File%3ACassiopea_jellyfish.jpg)(by(Jacopo(Werther([Public(domain],(via(Wikimedia(Commonse)!"Red Fish at Papahānaumokuākea Marine National Monument" (h=p://en.m.wikipedia.org/wiki/File:Red_Fish_at_Papah%C4%81naumoku%C4%81kea.jpg)(by(US(Fish(&(Wildlife(Service(R(Pacific(Region((CC(BY(2.0),(via(Wikimedia(Commonsf)( "Wildebeest(and(impala(drinking"((h=p://www.flickr.com/photos/dkeats/6037865141)(by(Derek(Keats((CC(BY(2.0)g)(“ladybirds(overwintering”((h=p://www.flickr.com/photos/94852245@N00/4057249053)(by(seier+seier((CC(BY(2.0)h)("Nasua(narica((foraging)"((h=p://commons.wikimedia.org/wiki/File%3ANasua_narica_%28foraging%29.jpg)(by(Hans(Hillewaert((CC(BYRSA(3.0),(via(Wikimedia(Commons
Slide-4Graph(by(Mark(Elgar
Slide-5Figure(2(from(Animal'Behaviour,(Volume(29.((Mark(A.(Elgar(&(Carla(P(Ca=erall,(Flocking(and(Predator(Suveillance(in(House(Sparrows:(Test(of(An(Hypothesis,(pages(868R872,(1981.((Reproduced(with(permission(from(Elsevier.
Slide-6---a)("Emperor(penguins"((h=p://en.wikipedia.org/wiki/File:Emperor_penguins.jpg)(by("NSF/Josh(Landis"([Public(domain],(via(Wikimedia(Commonsb)("DesertGrasslandWhiptailLizard(AspidoscelisUniparens56"((h=p://commons.wikimedia.org/wiki/File%3ADesertGrasslandWhiptailLizard_AspidoscelisUniparens56.jpg)(by("Ltshears"((CC(BYRSA(3.0),(via(Wikimedia(Commons((c)( "RUDDY(TURNSTONE(RUNNING(ALONG(SANIBEL(BEACH"((h=p://commons.wikimedia.org/wiki/File%3ARUDDY_TURNSTONE_RUNNING_ALONG_SANIBEL_BEACH.jpg)(by(Peter(Wallack((CC(BYRSA(3.0),(via(Wikimedia(Commonsd)("Suricata(surica=a(RAuckland(Zoo(RgroupR8a"((h=ps://commons.wikimedia.org/wiki/File%3ASuricata_surica=a_RAuckland_Zoo_RgroupR8a.jpg)(by(Ashleigh(Thompson((CC(BY(2.0),(via(Wikimedia(Commonse)("Nutmeg(Mannikin"((h=p://www.flickr.com/photos/pazzani/7504160732/)(by("Mike's(Birds"((CC(BYRSA(2.0)f)( "ghostRcrab_w725_h476"((h=p://www.publicRdomainRimage.com/faunaRanimalsRpublicRdomainRimagesRpictures/crabsRandRlobstersRpublicRdomainRimagesRpictures/ghostRcrab.jpg.html)(by(Harrison(George,(U.S(Fish(and(Wildlife(Service([Public(domain]
Slide-7-&-8-Birds(by(Milly(Formby(©(University(of(Melbourne
Slide-9a)(Birds(by(Milly(Formby(©(University(of(Melbourneb)(Green(Yellow(Cartoon(Bug(Insect((h=p://pixabay.com/en/greenRyellowRcartoonRbugRinsectR34375/)(by(Nemo([Public(Domain](via(pixabay
Slide-10Experimental(Approaches(Feeder(Diagram(by(Milly(Formby(©(University(of(Melbourne
Slide-11Graph(by(Mark(Elgar
Slide-13a)("The(Fence(Si=er"((h=p://www.flickr.com/photos/aussiegall/608251625/)(by(Louise(Docker((CC(BY(2.0)b)(‘Square(feeder(vs(long(feeder’(by(Milly(Formby(©(University(of(Melbourne(
Slide-14Flock(size(vs(Vigilance(graph(by(Mark(Elgar
Slide-16Data(sourced(from((Beauchamp,(G.)(Reduced(flocking(by(birds(on(islands(with(relaxed(predaUon.(Proceedings:'Biological'Sciences,(Vol(271.(No.(1543((2004),(pp.(1039(–(1042.((The(Royal(Society.
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