Predation Lecture 15

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PredationLecture 15
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• Overview
• Chapter in Text 15, 17
• Predation and Herbivory
• Responses of individuals to predation
• Responses of populations to predation refuges
• Importance of Predators
• Maintenance of ecosystem diversity
• as a Keystone species

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• What is a predator?
• Narrow sense
• Broad sense
• Ecological definition of predator
• Herbivores
• Grazers and browsers consume part of
  plant/plant not killed
• Seed eaters planktinovores consume entire
  plant
• Parasite generally do not kill host
• Parasitoid lay eggs in host feeding by larvae
  eventually kill host

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• Under simple laboratory conditions, the predator
  often exterminates its prey
• It then becomes extinct itself having run out of
  food!

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• Lotka-Volterra Models and Predator-Prey cycling
• Developed during 1920s
• Assume mutual interaction of predator and prey
  numbers
• Predict persistence of both predator and prey
  populations
• The LotkaVolterra equations for predator and
  prey populations link the two populations
• Each population functions as a density-dependent
  regulator on the other
• Predator as a source of density-dependent
  regulation on the mortality of the prey
  population
• Prey as a source of density-dependent regulation
  on the birthrate of the predator population

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• The paired equations, when solved, show that the
  two populations rise and fall in oscillations
• The cycle can continue indefinitely the prey is
  never quite destroyed the predator never
  completely dies out

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• Now, here you see, it takes all the running you
  can do, to keep in the same place the Red
  Queen
• Coevolution as prey species evolve ways to avoid
  being caught, predators evolve more effective
  means to capture them
• Natural selection (think in terms of fitness) ?
• smarter, more evasive prey
• smarter, more skilled predators

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• Prey defenses to avoid being detected, selected,
  and captured by predators
• Chemical defense
• Alarm pheromones
• Repellants
• Toxins
• Cryptic coloration
• Warning coloration
• Protective armor
• Behavioral defense

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Chemical Defenses

• Some animals receive an added benefit from eating
  plants rich in secondary chemical compounds
• Caterpillars of monarch butterflies concentrate
  and store these compounds

• They then pass them to the adult and even to eggs
  of next generation
• Birds that eat the butterflies regurgitate them

Im not eating this again!
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Plant Responses to Herbivores

• Physical
• Thorns
• Height
• Heavy seed coat
• Chemical
• Toxins
• Digestion inhibitors
• Nutritional
• Low levels of N in older foliage
• Tough, difficult to masticate foliage

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Chemical Responses of Plants to Herbivory

• Mustard oils protected plants from herbivores at
  first
• At some point, however, certain insects evolved
  the ability to break down mustard oil

• These insects were able to use a new resource
  without competing with other herbivores for it
• Cabbage butterfly caterpillars

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Animal Defenses against Predation

• Physical
• Behavioral
• Chemical
• Toxins
• Coloration
• Cryptic
• Warning coloration aposmatic
• Batesian mimicry harmless mimics
• After Henry Bates, a 19th century British
  naturalist
• Müllerian mimicry common coloration of toxin
  bearing spp
• After Fritz Müller, a 19th century German
  biologist

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Self Mimicry

• Involves adaptations where one animal body part
  comes to resemble another
• This type of mimicry is used by both predator and
  prey
• Example
• Eye-spots found in many butterflies, moths and
  fish

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Müllerian Mimicry

• Two or more unrelated but protected (toxic)
  species come to resemble one another

• Thus a group defense is achieved

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• Predation and Behavior Modification - Refuges
• Schooling of prey fish response to predator
  attack some survive
• Alarm calls Prairie dogs, ground squirrels
• Song birds mob and harass predator bird species
• Avoidance temporal, spatial
• Refuges

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Refuges

• A mechanism that allows exploited population to
  escape predation/parasitism many forms
• Place/form of cover, schooling, synchronized
  reproduction (large numbers at one time), size
• May not provide absolute sanctuary, enough for
  species to survive
• Important for survival of predator too!

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Protection in Numbers

• Living in a large group provides a refuge.
• Predators response to increased prey density
• Prey consumed x Predators Prey Consumed
• Predator Area Area
• Wide variety of organisms employ predator
  satiation defense.
• Prey can reduce individual probability of being
  eaten by living in dense populations.

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Examples of Predator Satiation

• Synchronous widespread seed and fruit production
  by plants - masting.
• Synchronized emergence of Cicadas 16-17 year
  cycle
• Williams estimated 1,063,000 cicadas emerged from
  16 ha study site.
• 50 emerged during four consecutive nights.
• Losses to birds was only 15 of production

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• Size As A Refuge
• If large individuals are ignored by predators,
  then large size may offer a form of refuge.
• Peckarsky observed mayflies (Family
  Ephenerellidae) making themselves look larger in
  the face of foraging stoneflies.
• In terms of optimal foraging theory, large size
  equates to lower profitability.

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• Is regulation top-down or bottom-up?
• ie. primary productivity versus limits imposed by
  predator populations

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Ch 18 p 344
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• Diffuse predatorprey interactions
• The lynx, coyote, and horned owl are responsible
  for the periodic cycles in the snowshoe hare
  population
• Diffuse mutualism
• A single plant species may depend on a variety of
  animal species for successful reproduction

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Hare popul crashes as 1. Reduced forage ?
weakened hares, high lynx prdation 2. Forage
produced after heavy browsing accumulates plant
defense chemicals ?less palatable
Lynx predates weakened hares eventually crashes
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• Is regulation top-down or bottom-up?
• ie. primary productivity vs. limits imposed by
  predator populations

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• Predators and Diversity see pages 340-344
• Alter competitive balance amongst prey spp.
• Robert Paine studies sea star exclusion in
  intertidal plots ? decreased prey diversity (15 ?
  8 spp)
• Selective alteration of competitive relationships
• Peter Morin studies altered competitive
  relationships amongst immature frog spp by
  predatory newt

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• Keystone Predator (or Keystone Consumer )
• Species essential to maintenance of ecosystem
  structure/diversity
• Example (there are many) CA sea otter kelp
  forest community

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• THINGS TO WORRY ABOUT
• Your Pores Portals for Invasion?
• Musty Dankness
• Fleas Ticks Tiny TerroristsWhat's Embedded
  in Your Bed?
• What Your Mother Never Told You About Those
  Hidden Corners and Cracks
• Pink Mold Slime or Scourge?Mildew Mold's
  Evil Twin