Life Histories

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Life Histories

• Animals
• 1. Size at reproductive maturity
• Your clutch size database SVL of reproductive
  females
• tesselata 91 102 mm
• neotesselata 81 99 mm
• sexlineata 69 75 mm
• 2. Age at reproductive maturity
• 3. Number of offspring produced (e.g., clutch
  size)
• 4. Size of offspring produced
• Plants
• Short vs. long life spans
• Fast vs. slow growth rates
• Low vs. high investment in seed production

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• Life cycle variation from two sources
• 1. Epigenetic factors
• Phenotypic plasticity
• 2. Adaptations
• Set by genotypes

Scaphiopus multiplicata
Polyphenism Different morphs
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Energy allocation principle and reproduction

• Energy available to an individual is finite
• A constraint on r (intrinsic rate of increase)
• Energy shunts
• 1. maintenance
• 2. growth
• 3. reproduction
• Energy constraints on reproduction result in two
  fundamental strategies
• 1. Large number of small young chance of
  individual survival small.
• 2. Small number of large young chance of
  individual survival good.

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Clutch size

• Optimal clutch size
• How much energy should a female allocate to a
  reproductive episode e.g., how many eggs?
• The trade-off the more offspring produced, the
  fewer resources available for each individual.
• Lacks prediction Natural selection should favor
  a clutch size that maximizes the number of
  surviving offspring.
• Clutch size should be a reproductive strategy.

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Figure 7.16 Egg SizeEgg Number Trade-Off in
Fence Lizards (Part 1)
Geographic variation in clutch and egg size
Sceloporus occidentalis
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Figure 7.16 Egg SizeEgg Number Trade-Off in
Fence Lizards (Part 2)
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Interspecific life history variationGeneralities
vertebrates

• Reproductive maturity
• Achieved quickly in species with high adult
  mortality.
• Delayed in species with high adult survival.
• Achieve larger body sizes

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• Many life history concepts derived from bird
  studies.
• Reproductive output is accessible.
• Reproductive output can be easily manipulated and
  adjusted.
• Individuals can be marked for identification.

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Clutch size of mother can affect clutch size of
daughters
Collared flycatcher
Marked for subsequent identification
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Age at first reproduction and size of first
clutch can affect subsequent clutch size

• Collared Flycatcher

Begin with extra eggs
Begin reproducing at different ages
controls
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How large should offspring be?

• Trade-off between number and size of offspring.
• Many small OR few large?
• May be dictated by the environmental context
  i.e., the reproductive strategy may include
  phenotypic plasticity
• e.g. Seed beetle

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Seed beetle Stator limbatus
Blue palo verde seed Poor host lt 1/2 larvae
survive
Cat-claw acacia seed Good host most larvae
survive
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The model Larval size increases with
an decreased number of sibs
Number of offspring
Minimum size at which offspring survive is
smaller on good host
Offspring survival
Optimal offspring size for parent is larger on
poor host. Prediction Lay larger eggs on poorer
host
Parental fitness
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Cat-claw (good)
Blue paloverde (poor)
Performance on one host.
Female lays first egg on seed of one host. Then
female moved to the different host seed to lay
other eggs.
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Reproductive mode and the cost of sex. Female
can only contribute ½ of her genes to each
offspring
Female contributes all of her genes to each
offspring
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• Reproductive strategies
• 1. Species reproduce once
• Semelparous (adj.) reproduce once in their
  lifetime.
• salmon Agave?
• semelparity (n.)
• Maximize success by producing large numbers of
  propagules
• or offspring.
• 2. Species reproduce more than once in their
  lifetime.
• Iteroparous (adj.) reproduce several to many
  times before dying.
• iteroparity (n.)
• Counters environmental uncertainty

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Semalparity?
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Ends of a spectrum of life history strategies
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