Predation

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Predation
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Hypotheses for Patterns of Diversity

• Evolutionary Time
• Ecological Time
• Primary Production
• Stability of Primary Production
• Structural (Habitat) Diversity
• Climatic Stability
• Competition
• Predation

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Predation

• In an ecological sense, predation is not just
  carnivores like wolves eating musk oxen, or
  coyotes eating mice.
• In fact, deer are acting as predators on plants,
  parasites act as predators on their hosts, and
  mice act as predators on the seeds they eat.
• The difference here is in the extent of the
  effect.

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Predation

• Carnivory capture, kill, and consume an animal.
• Herbivory consumption of plant material by an
  animal.
• Grazer/folivore consumes leafy material
• Browser consumes woody material and bark.
• Granivore consumes seeds
• Frugivore consumes fruit
• Exudivore consumes exudates like sap.

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Predation

• Parasitism association w/ host. Objective is
  to keep host alive. Generally, parasite stays
  with same host throughout its life.
• Parasitoids parasitic activities limited to
  larval stages.

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Predation

• Carnivorous predation
• predator must locate, capture, and consume prey.
• Mammalian predators employ a diversity of
  morphological, physiological, and behavioral
  techniques to to this.
• Reptilian predators do this as well. Compare a
  monitor lizard with a snake.

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Predation

• Prey detection and recognition
• Search image.
• Smell - chemoreception
• Sound - bats and marine carnivores.
• Prey capture
• Stalk and ambush
• Finess.
• Pure power.

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Prey Adaptations

• Avoiding detection
• Crypsis
• Avoiding capture
• Herd behavior in ungulates safety in numbers
  and increased vigilance.
• Detection of predator as in kangaroo rats.
• High speed locomotion, or use of refugium.
• Display as in baboons.
• Chemical defense as in skunks and toads.
• Body armor as in turtles.

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Herbivorous Predation

• Herbivores use a variety of devices to improve
  efficiency
• Pectinate teeth in dermopterans.
• Thumb in giant panda
• Elongated intestines and ceacum and/or ruminant
  stomach.

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Plant Adaptations to Herbivores

• Chemical defenses such as tanins
• Grey and fox squirrels and red and black oak
  acorns.
• Synchronous flowering or seed set swamps
  potential herbivores safety in numbers.
• Structural adaptations spines in cacti and
  euphorbs.

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Effects of Herbivory

• For the most part, herbivory is not good for the
  plant. However,
• Grazing may increase production in some cases.

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Optimal Foraging

• Predators are under intense selection pressure to
  find and consume prey.
• We expect that organisms should forage in a way
  that optimizes their inclusive fitness.
• How can this be done?
• 2 ways Energy Maximizers and Time Minimizers.

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Optimal Foraging

• Energy maximizers
• Get maximum possible energy return under a given
  set of foraging conditions EMs get the maximum
  amount of energy possible.

• Time minimizers
• Get maximum possible energy return under a given
  set of foraging conditions TMs obtain a given
  amount of energy in the min. amt. of time.

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Optimal Diet

• There is a trade-off between a specialized diet
  and a generalized one
• Specialized diet food items are of high value,
  but may require extensive search energy or search
  time. These items may also require extensive
  handling.
• Generalized diet food items may be more
  abundant, but will not be of equal value.

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Optimal Foraging

• Each item consumed contributes to the average
  energy input. The better diet is the one that
  increases the average energy input.
• The question becomes, should the organism broaden
  its diet or narrow its diet?

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Optimal Foraging

• Energy input per item can be written as

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Optimal Foraging

• In this formulation, we compare the caloric
  content of each item, to the handling time (or
  energy) required to capture, subdue, and consume
  that item.
• Lets create a model that will allow us to predict
  what an organism should do.

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Optimal Foraging

• Define the amount of time spent searching for
  prey as Ts seconds.
• Our predator encounters 2 types of prey at rates
  ?1 and ?2 prey per second.
• These prey items contain E1 and E2 calories, and
  take h1 and h2 seconds to handle.

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Optimal Foraging

• If the predator spends Ts seconds searching for
  prey, it will encounter
• n1 Ts ?1 type 1 prey
• n2 Ts ?2 type 2 prey

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Optimal Foraging

• The total energetic return, E, will be equal to
  the number of encounters times their respective
  energetic contents.
• E n1E1 n2E2

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Optimal Foraging

• The total time spent handling these prey items
  will be
• Th n1h1 n2h2

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Optimal Foraging

• Substituting for n1 and n2, we get

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Optimal Foraging

• The total time spent handling prey is given by

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Optimal Foraging

• So, the total time spent searching for and
  handling prey will be

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Optimal Foraging

• And the energetic return per unit time spent
  searching for and handling prey becomes

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Optimal Foraging

• This simplifies to

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Optimal Foraging

• Try an example. Suppose our optimal forager has
  100 seconds to search for prey. It encounters
  prey type 1 at a rate of 0.10/s, and prey type 2
  at 0.01/s. Thus,
• ?1 0.1
• ?2 0.01

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Optimal Foraging

• Also, prey type 1 contains 10 calories and takes
  5 seconds to handle, while prey type 2 contains
  10 calories and takes 10 seconds to handle.
• E1 10 E2 10
• h1 5 h2 10
• Should our predator be a generalist or a
  specialist?

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Marginal Value Theorem
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Marginal Value Theorem