Predator Ecology: Evolutionary Ecology of the Functional Response

177 Pages·2021·11.864 MB·English

by  John P. DeLong

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Predator Ecology
OUPCORRECTEDPROOF – FINAL,25/6/2021,SPi
OUPCORRECTEDPROOF – FINAL,25/6/2021,SPi
Predator Ecology
Evolutionary Ecology of the
Functional Response
John P. DeLong
SchoolofBiologicalSciences,UniversityofNebraska-Lincoln
andCedarPointBiologicalStation,USA
1
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OUPCORRECTEDPROOF – FINAL,25/6/2021,SPi
Contents
Prologue vii
1. Introduction 1
1.1 Functionalresponsesandfoodwebs 3
2. TheBasicsandOriginofFunctionalResponseModels 9
2.1 Typesoffunctionalresponses 9
2.2 Predatordependenceofthefunctionalresponse 18
2.3 Relationshiptoalternativeformulationsinaquaticliterature 20
2.4 TheRogersRandomPredatorequation 21
3. WhatCausesVariationinFunctionalResponseParameters? 27
3.1 Variationinfunctionalresponseparameters 27
3.2 Breakingdownthespaceclearancerate 29
3.3 Factorsaffectingspaceclearancerate 32
3.4 Breakingdownthehandlingtime 40
3.5 Limitsontheparameterspace 42
3.6 Otherpredators 44
4. PopulationDynamicsandtheFunctionalResponse 47
4.1 Thefunctionalresponseasatrophiclink 47
4.2 Addingsomecomplexity 48
5. Multi-speciesFunctionalResponses 55
5.1 TheneedforMSFRs 55
5.2 Extendingthefunctionalresponsetomultiplepreytypes 58
5.3 Anexamplewithdamselflynaiads 61
6. SelectiononFunctionalResponseParameters 65
6.1 Whyfunctionalresponseparametersmightchangethroughevolution 65
6.2 Adynamictug-of-war 68
6.3 Temporalvariationinthestrengthofselection 70
6.4 Traitslinkedtofunctionalresponseparameters 74
6.5 Linksamongpredator–preymodelparameters 75
7. OptimalForaging 79
7.1 Pickingpreytypestoincreasefitness 79
7.2 Derivingthestandardpreymodeloptimalforagingrule 80
7.3 OFTremainsusefulandneedsfurthertesting 84
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vi Contents
8. DetectingPreyPreferencesandPreySwitching 89
8.1 Preyselectioninthepresenceofalternateprey 89
8.2 Detectingpreyswitching 90
8.3 Nullexpectationsfromthefunctionalresponse 92
8.4 NullexpectationsforManly’sα 97
9. OriginoftheTypeIIIFunctionalResponse 101
9.1 WhatgeneratesatypeIIIfunctionalresponse? 101
9.2 ConcernsaboutthestandardtypeIIImodel 106
9.3 AnalternativetypeIIImodel 108
10. StatisticalIssuesintheEstimationofFunctionalResponses 115
10.1 Curvefitting 115
10.2 Noiseandthenatureofforagingtrialdata 118
10.3 Differencesbetweenparameters 125
10.4 TypeIIortypeIII? 127
11. ChallengesfortheFutureofFunctionalResponseResearch 133
11.1 MSFRs 133
11.2 Sourcesofvariationinparametersandconstraints 135
11.3 Functionalresponsemodels 138
11.4 Linkingfunctionalresponsesfromforagerstocommunities 140
11.5 Accountingfortimespentonotheractivities 143
Epilogue 145
References 147
Index 166
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Prologue
The motivation for this book was three-fold. First, I personally wanted to
learn more about functional responses. I found, however, that information
about functional responses in the literature is piecemeal. In no place could
I find a synthesis about them, despite the existence of thousands of papers
describingorparameterizingfunctionalresponsesforallmannerofpredators
andprey.Second,therewasclearconflictintheliteratureaboutwhatmodels
tousetodescribefunctionalresponses,thebiologicalmeaningofthemodel
parameters, and why functional responses vary among predator–prey pairs
andacrossenvironmentalortrait-basedgradients.
Third,andperhapsmostimportantly,thefunctionalresponsebecamethe
core concept for my field-based course called Predator Ecology. I wanted to
providemystudentswithanoverviewofthefundamentalsandthebiological
relevance of functional responses, so that in short order they could inter-
pret papers, conduct their own experiments, and grasp how natural selec-
tion might be shaping predator–prey interactions and therefore food webs.
Ineededtostartsynthesizingforthecourse,resolveconflictsinterminology
and models, and help students connect the math to the biological reality of
nature.Thatwasthebirthofthisbook.
So for me and anyone else, this book covers the fundamentals and then
offers a deep dive into what functional responses really are, how to think
about them, why they are relevant to pretty much anything ecological, and
where studies on functional responses might go in the future. This book is
whatIneededwhenIstartedteachingthePredatorEcologyclass.Thisbook
is intended for advanced undergraduate students and graduate students, as
well as anyone interested in functional responses. The book moves between
simple introductions, derivations of the core models, reinterpretations and
clarifications of the parameters and the functions themselves, and novel
hypotheses about functional responses and their consequences. For anyone
mostlyinterestedintheconceptsandbiologicalrelevance,itmaybeusefulto
skipoversomeofthederivationsandfocusonthebiologicalmeaningoffunc-
tionalresponsesandtheirparameters.Thencomebacktotheequationslater.
To support hands-on learning as well as new research into functional
responses, the book is accompanied by a full set of code to reproduce all
data and analysis-based figures in the book. This code is written for Matlab
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viii Prologue
© but could be translated to other scientific programming languages. The
code, and associated data as necessary, are hosted in a zipped folder at
www.oup.com/companion/DeLongPE. Any corrections or updates to the
codewillbepostedatthissite.
Thisbookwouldnothavebeenpossiblewithoutthepatienceandsupport
ofallthepeoplewhohavetakenandTA’dmyPredatorEcologyclassbothon
CityCampusatTheUniversityofNebraska-LincolnandoutatCedarPoint
BiologicalStation.Theirinvolvementhashelpedtokeepthemomentumon
my predator ecology research going. I appreciate the helpful comments on
drafts of this manuscript from Stella Uiterwaal, Kyle Coblentz, and Mark
Novak.Icouldnothaveunderstoodtherootsumofsquaresexpression(see
Chapter 3) without the help of Van Savage. I’d like to give a shout-out to
HawkWatch International (www.hawkwatch.org), where I got my start in
predatorecologyshortlyaftercollege.Finally,noneofwhatIdowouldmake
sensewithouttheloveandsupportofJess,Ben,andPearl,whomakemyheart
soarlikeahawk.
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1
Introduction
Predators seem to be universally fascinating. Maybe that is because we
humans are predators, or because we can be prey for other predators
(Quammen, 2004). Maybe we are just morbidly curious about death.
Whatever the reason, I have noticed that nature shows tend to focus a lot
onpredator–preyinteractions:thedramaofthepredator’shuntortherelief
of the prey’s escape. We are drawn to predation and intuitively understand
that it is a fundamental part of nature. Indeed, what a predator eats is often
amongthefirstthingsthatwelearnaboutit,suggestingthatwhoeatswhom
isamongthemostcentralfeaturesofecologicalsystems,oratleastcentralto
thewayweimaginethem(SihandChristensen,2001).
Predation is fundamental beyond the event of a predator capturing prey.
The rate of predation and the identity of the prey combine to direct the
flowofenergythroughecologicalcommunities.Asaresult,predationplays
a key role in structuring food webs. Of course, there are other ways that
energy flows through communities that do not involve predation, such as
photosynthesis,herbivory,parasitism,decomposition,andtheconsumption
of detritus or nectar. These are all equally crucial, but consuming other
organisms is a widespread way of getting that energy, so understanding the
rate at which predators consume prey is a necessary part of understanding
ecologicalsystems.
Sowhatcontrolstherateatwhichpredatorsconsumeprey?Manythings.
Predatortraitslikeclaws,preydefenseslikecamouflage,habitatcomplexity,
hunger, and the presence or behavior of other predators all play their part.
Amongthesemanyinfluences,oneofthebiggestfactorsisthenumberofprey
available to be consumed. Generally, predators have a higher foraging rate
whentherearemorepreytobehad—uptoapoint.Therelationshipbetween
foraging rate and prey abundance (or density) is known as the functional
response(Holling,1959;Solomon,1949)(Figure1.1).
Thefunctionalresponseisadescriptionofhowmanypreyapredatorwould
beexpectedtoeatgivenaparticularamountofpreyavailabletothepredator,
wherever they are searching for food. That expected number depends on
the behavior and morphology of both predator and prey in the context of
PredatorEcology:EvolutionaryEcologyoftheFunctionalResponse.JohnP.DeLong,OxfordUniversityPress.
©JohnP.DeLong2021.DOI:10.1093/oso/9780192895509.003.0001