Foraging Ecology: An introduction to predation

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Foraging Ecology An introduction to predation
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Feeding Modes or Trophic Categories

• Detritivores
• Scavengers
• Herbivors
• Grazers
• Browsers
• Phytoplanktivores

• Omnivores
• Predators
• Benthivores
• Aerial feeders
• Piscivores
• Zooplanktivores

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Aerial Predators
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Benthivore Predators
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Piscivore Predators
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Zooplanktivorous Predators
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Zooplankton
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Adaptations of Zooplanktivores

• Gill rakers
• Number and spacing

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Capture and Retention Gill rakers in
planktivorous fish
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Adaptations of Zooplanktivores

• Gill rakers
• Number and spacing
• Mouth size and shape
• Small and round
• Swimming morphology
• Fusiform shape, fin placement minimizes drag

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The predation cycle

• Prey Location (detection)

Pursuit
Attack
Retention
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Predation cycle Detecting prey

• Active
• Moving search primarily with vision, but can use
  other 5 senses
• Primary method utilized by zooplanktivores
• Passive
• Lie and wait or ambush predators
• Method driven by prey availability and behavior

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Factors influencing active prey detection

• Size of prey
• Reaction distance max distance predator can
  detect prey increases as size of prey increases

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Prey Location-Size matters
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Factors influencing active prey detection

• Size of prey
• Reaction distance max distance predator can
  detect prey increases as size of prey increases
• Ontogenic shift in size selection
• Preference for large vs. small
• Apparent size hypothesis small, close versus
  large, far

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Gape Limitation
From DeVries et al. 1998.
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Factors influencing active prey detection

• Size of prey
• Availability
• Vertical migrations
• Cover
• 3. Illumination and color

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Reaction distance or detection f (Light)
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Prey detection f (Pigmentation)
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Contrast
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Factors influencing active prey detection

• Size of prey
• Availability
• Vertical migrations
• Cover
• Illumination and color
• Movement

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Prey detection f(Movement)
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The predation cycle

• Prey Location

After location until time fish gets close enough
to grab prey
Pursuit
Attack
Retention
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The predation cycle

• Prey Location

Point in cycle where choice is exercised (OFT)
Pursuit
Attack
Retention
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To pursue or not to pursue

• Choice based on
• Difficult of handling prey
• Experience with taste or morphology
• Degree of hunger
• Planktivores rarely avoid prey b/c size
• Size-selective predation active choice
• Selection for larger individuals

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Handling Time
Wooton 1990
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Optimal foraging theory

• Optimization of what, when, and where animals eat
• Evolutionary expectation for efficient foraging
• Optimal performance min cost and max gain
• Food types, locales, times, and methods

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The predation cycle

• Prey Location

Pursuit
Prey is inhaled
Attack
Retention
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Visual versus non-visual

• Visual detect and pursue prey. Prey consumed via
  inertial sucking
• Suction f(mouth size, volume of buccal cavity,
  rate of mouth opening
• Prey specific tactics (copepods vs. cladocerans)
• Countered by evasion capabilities of prey

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Evasion copepods vs. cladocerans
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Visual versus non-visual

• Visual detect and pursue prey. Prey consumed via
  inertial sucking
• Suction f(mouth size, volume of buccal cavity,
  rate of mouth opening
• Prey specific tactics (copepods vs. cladocerans)
• Non-visual detection and pursuit less important
• Filtering and pump feeding low light levels,
  less discriminating, many fine gill rakers.

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Prey capture f (density and cover)
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The predation cycle

• Prey Location

Pursuit
Attack
Retention
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Prey retention

• Morphology of predator gill raker spacing and
  volume of water
• Taste
• Morphology spiny versus soft-rayed
• Size
• Position of capture

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Part IIDirect and indirect effects of predation
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Predation, being eaten

• Consumption of all or part of one living organism
  by another
• Any interaction when energy flows from one
  individual to another (/-)
• Direct effects
• Indirect effects

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Direct versus indirect effects

• Direct consumption or death (e.g., reduced
  population densities) lethal effects
• Indirect
• A. non-lethal effects (e.g., change in behavior,
  size structure, community composition, growth)
• B. When the influence of one species on another
  is mediated by some intermediate species

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Indirect effects lake food webs
Piscivore
(-)
Planktivore
()
Herbivore (zooplankton)
(-)
Phytoplankton
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Direct versus indirect effects

• Direct lethal
• Indirect non-lethal

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Case study of direct and indirect effects of
predation on fish communities

• He and Kitchell 1990 Transactions
• Whole-lake experiment in Wisconsin
• Introduced northern pike (Esox lucius)
• Monitored fish populations and environmental
  conditions pre- and post-introduction

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Case study He and Kitchell

• Response variables
• Direct consumption of prey (densities)
• Indirect community composition, behavior
  (foraging, migrations), size structure

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He and Kitchell 1990Direct Effects
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Indirect EffectsCommunity CompositionHe
and Kitchell 1990
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Indirect EffectsEmigrationImmigrationHe
and Kitchell 1990
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Indirect EffectsSize structureHe and
Kitchell 1990
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He and Kitchell 1990

• Direct reduced density
• Indirect
• Altered community composition (decrease dominant
  and increase rare)
• Reduced size distribution in lake through
  predation, but also emigration

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What about prey adaptations?
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Zooplankton adaptations to predation

• Maximize invisibility
• Minimize size, but costs. Thus
• Clear carapaces
• Helmets
• Gelatinous sheaths
• Lateral compression
• Reproduction
• Copepods versus cladocerans
• Evasion
• Vertical migrations
• Avoid suction

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Case study morphological changes to reduce
predation pressure (Bronmark and Miner 1992)

• Crucian carp
• Lakes with pike, small large individuals
• Large (dorso ventral height)
• Lakes w/out pike, large of small individuals
• Formerly thought to be a result of resource
  availability, more food, more deep-bodied
• Eutrophic ponds, divided in ½, added pike to one
  ½

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Indirect EffectsBronmark and Miner 1992

• P/A pike
• Morphology of carp
• Deeper bodied

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Indirect EffectsBronmark and Miner 1992

• Pike gape limited
• Increased handling times
• Size refuge

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Causes of altered morphology

• Selective predation
• Increased resource availability
• Predator induced phenotypic plasticity

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Indirect EffectsBronmark and Miner 1992

• Phenotypical change in
• resource allocation
• Costs implied
• Drag 32 greater
• Plasticity best
• Why?
• How evolved?

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