Chapter 10 Brief Overview

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Chapter 10 (Brief Overview)
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But first, review
Joseph Grinnell

• Resource Utilization Curve
• How is it related to the niche?
• Niche discussion
• How is it related to acclimation?
• Not a constant set of environmental conditions
• Questions about this stuff?

Charles Elton
GE Hutchinson
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What is life history?

• The life history is the schedule of an organisms
  life, including
• age at maturity
• number of reproductive events
• allocation of energy to reproduction
• number and size of offspring
• life span

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Compare

• Elephant
• Life span 50y
• Age at 1st reproduction 13-20yrs
• Gestation 21-22m
• young 1
• Parental care
• ? - none
• ? - herd consists of matriarch, male and female
  offspring until 12y, then male offspring leave
  herd, female offspring stay.

• Salmon
• Life span 1-8y
• Age at 1st reproduction
• 1-8y
• Gestation how long it takes to swim from ocean
  to spawning grounds
• young (eggs)
• 2500 - 7000
• Parental care
• ? - none
• ? - none

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Survivorship curves
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What influences life histories?

• Life histories are influenced by
• body plan and life style of the organism
• evolutionary responses to many factors,
  including
• physical conditions
• food supply
• predators
• other biotic factors, such as competition

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A Classic Study

• David Lack of Oxford University first placed life
  histories in an evolutionary context
• tropical songbirds lay fewer eggs per clutch than
  temperate counterparts
• Lack speculated that this difference was based on
  different abilities to find food for the chicks
• Temperate breeders have longer days in which to
  find food than tropical breeders

Snow bunting
Red-headed manakin
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Lacks Proposal

• Lack made 3 key points
• because life history traits (i.e. of
  eggs/clutch) contribute to reproductive success
  they influence evolutionary fitness
• life histories vary in a consistent way with
  respect to factors in the environment (reaction
  norms)
• hypotheses about life histories are subject to
  experimental tests
• Therefore Life history is shaped by natural
  selection and are amenable to scientific method

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An Experimental Test

• Lack
• Artificially increase of eggs/clutch.
• There would be no reduction in success.
• Therefore, the number of offspring is limited by
  food supply
• This proposal has been tested repeatedly
• Gören Hogstedt (1980) manipulated clutch size of
  European magpies
• maximum number of chicks fledged corresponded to
  normal clutch size of seven

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• Hogstedt (1980) Magpies (Pica pica)
• Perrins and Moss (1975) Great tits (Parus major)

Expected w/ No resource limitations
Predicted by Lack Observed
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Components of Fitness

• Generic offspring in next and future gens.
• Genetic proportion of alleles in next and future
  gens.
• Fitness, ultimately dependent on producing
  successful offspring
• Components
• maturity (age at first reproduction)
• parity (number of reproductive episodes)
• fecundity (number of offspring per reproductive
  episode)
• aging (total length of life)

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Life Histories A Case of Trade-Offs

• Organisms face a problem of allocation of scarce
  resources (time, energy, materials)
• the trade-off resources used for one function
  cannot be used for another function
• Remember
• Altering resource allocation affects fitness.
• Consider the possibility that an oak tree might
  somehow produce more seed
• how does this change affect survival of
  seedlings?
• how does this change affect survival of the
  adult?
• how does this change affect future reproduction?

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Concept of renewal
Now P Year 1 P(1r) Year 2 P(1r)2 Year 3
P(1r)3
Choices
Self survival? Parental care?
How often do I breed?
Few large? Many small?
How fast growth and maturity?
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Life histories resolve conflicting demands.

• Life histories represent trade-offs among
  competing functions
• a typical trade-off involves the competing
  demands of adult survival and allocation of
  resources to reproduction
• kestrels with artificially reduced or enlarged
  broods exhibited enhanced or diminished adult
  survival, respectively
• Hence parental cost.

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The life table