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					       Life Histories         Chapter 12
Adaptation of an organism that influence its biology over
its life span; e.g. offspring #; survival, size and age of
reproduction, maturation transformations.




                                                             1
          Offspring Number Versus Size
•   Principle of Allocation: If organisms use
    energy for one function such as growth, the
    amount of energy available for other
    functions is reduced.
      Leads to trade-offs between functions

       such as number and size of offspring.




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3
12_04.jpg




            4
12_07.jpg




            5
        Seed Size and Number in Plants


•   Small plants producing large number of
    small seeds appear to have an advantage in
    areas of high disturbance.

•   Plants producing large seeds are
    constrained to producing fewer seedlings
    more capable of surviving environmental
    hazards.

                                               6
        Seed Size and Number in Plants
•   Jakobsson and Eriksson found seed size
    variation explained many differences in
    recruitment success.
      Larger seeds produce larger seedlings

       and were associated with increased
       recruitment.




                                               7
         Seed Size and Number in Plants
•   Seiwa and Kikuzana found larger seeds
    produced taller seedlings.
      Energy reserve boosts seedling growth.

         Rapid growth helps seedling penetrate

          thick litter layer.




                                                  8
12_06.jpg




            9
        Seed Size and Number in Plants
•   Many families produce small number of
    larger seeds.
      Dispersal mode might influence seed size.




                                               10
      Life History Variation Among Species
•   Shine and Charnov pointed out vertebrate
    energy budgets are different before and after
    sexual maturity.
      Before - maintenance or growth.

      After - maintenance, growth, or

       reproduction.
      Individuals delaying reproduction will grow

       faster and reach a larger size.
         Increased reproduction rate.


                                                 11
12_03.jpg




            12
        Life History Variation Among Species
•   Gunderson found clear relationship between
    adult fish mortality and age of reproductive
    maturity.
      Species with higher mortality show higher

       relative reproductive rate.




                                               13
http://aquanic.org/images/photos/ingvar/Roughy.gif

 http://fish.dnr.cornell.edu/nyfish/Cyprinodontidae/mummichog.jpg


 •   Species that are short-lived with high mortality rate,
     mature fast, are often smaller and with high
     reproductive rate – population turnover
     (replacement) is fast.

 •   Long-lived species that mature slowly have lower
     mortality and lower reproductive (or recruitment)
     rate – population turnover is slow.


 •   Consider fish; which can be harvested with least
     negative impact on their populations?
                                                                    14
            Life History Classification
•   MacArthur and Wilson
     r selection (per capita rate of increase)

        Characteristic high population growth
         rate.
     K selection (carrying capacity)

        Characteristic efficient resource use.

•   Pianka : r and K are ends of a continuum,
    while most organisms are in-between.
     r selection: Unpredictable environments.

     K selection: Predictable environments.

                                                  15
r   K




        16
                Plant Life Histories
•   Grime proposed two most important
    variables exerting selective pressures in
    plants:
      Intensity of disturbance:

         Any process limiting plants by

          destroying biomass.
      Intensity of stress:

         External constraints limiting rate of

          biomass production.

                                                  17
               Plant Life Histories
•   Four Environmental Extremes:
     Low Disturbance : Low Stress

     Low Disturbance : High Stress

     High Disturbance : Low Stress

     High Disturbance : High Stress




                                       18
                Plant Life Histories
•   Ruderals (highly disturbed habitats)
     Grow rapidly and produce seeds quickly.

•   Stress-Tolerant (high stress - no disturbance)
     Grow slowly - conserve resources.

•   Competitive (low disturbance low stress)
     Grow well, but eventually compete with

      others for resources.



                                                19
Grime’s Plant Life History Triangle




                                      20
            Opportunistic, Equilibrium,
            and Periodic Life Histories
•   Winemiller and Rose proposed new
    classification scheme based on:
      juvenile survivorship (lx),

      fecundity (mx), and

      age of reproductive maturity (α)



     Opportunistic:   low lx - low mx - early α
     Equilibrium:     high lx - low mx - late α
     Periodic:        low lx - high mx - late α
                                                   21
Opportunistic, Equilibrium,
and Periodic Life Histories




                              22
12_22a.jpg




             23
12_22b.jpg




             24
25
12_22d.jpg




             26
12_22.jpg




            27
     Reproductive Effort, Offspring Size, and
              Benefit-Cost Ratios
•   Charnov developed a new approach to life
    history classification.
      Took a few key life history features and

       converted them to dimensionless
       numbers.
         By removing the influences of time and

          size, similarities and differences
          between groups are easier to identify.


                                                   28
12_23.jpg




            29
Reproductive Effort, Offspring Size, and
         Benefit-Cost Ratios




                                           30

				
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posted:10/15/2012
language:English
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