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LIFE HISTORIES. Chapter 12. Chapter Concepts. Finite resources require trade-off between number and size of offspring; few larger offspring vs. many smaller offspring

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life histories

LIFE HISTORIES

Chapter 12

Molles: Ecology 2nd Ed.

chapter concepts
Chapter Concepts
  • Finite resources require trade-off between number and size of offspring;
    • few larger offspring vs. many smaller offspring
  • With low adult survival, organisms reproduce earlier, invest more energy in reproduction; when adult survival is higher, organisms wait to reproduce until older, = less energy for repro
  • Life histories can be classified by pop. characteristics such as mx, lx

Molles: Ecology 2nd Ed.

offspring number versus size
Offspring Number Versus Size
  • Principle of Allocation – If organisms use energy for something like growth, energy for other functions is reduced
    • Leads to trade-offs between functions such as number and size of offspring

Molles: Ecology 2nd Ed.

egg size and number in fishes
Egg Size and Number in Fishes
  • Fishes have more variation in life-history than any other group of animals
    • Sharks produce 1-2 large eggs
    • Ocean sunfish produce 600,000,000 eggs

Molles: Ecology 2nd Ed.

turner and trexler study of darter life history traits
Turner and Trexler: study of darter life history traits
  • Their question was:
    • Is there a relationship between life history traits and gene flow?

Molles: Ecology 2nd Ed.

why these 15 darter species
Why these 15 darter species?
  • Variation in life history
  • Variation in body size (44 - 127 mm)
  • Variation in egg size (0.9 - 2.3 mm)
  • Variation in number of eggs (49 - 397)

Molles: Ecology 2nd Ed.

darters
Darters:

Molles: Ecology 2nd Ed.

turner trexler
Turner + Trexler
  • 1. Big darters produce more eggs that are smaller:

Molles: Ecology 2nd Ed.

slide10
Turner and Trexler guessed that larvae from larger eggs hatch earlier, feed earlier, don’t drift as far, and thus don’t disperse as far
    • Less dispersion = greater isolation = rapid gene differentiation

Molles: Ecology 2nd Ed.

gene flow
Gene flow?
  • Look at proteins (or DNA sequence)
  • Variation in proteins (size, shape)
  • More variation = less genetically similar pop’s
  • Less variation = more similar = more gene flow

Molles: Ecology 2nd Ed.

slide12

Fig 12.5

Molles: Ecology 2nd Ed.

seed size and number in plants
Seed Size and Number in Plants
  • Many families produce small # of large seeds
    • Dispersal mode might influence seed size

Molles: Ecology 2nd Ed.

seed size and number in plants1
Seed Size and Number in Plants
  • Westoby et.al. recognized four plant forms:
    • Graminoids – Grass and grass-like plants
    • Forbs – Herbaceous, non – graminoids
    • Woody Plants – Woody thickening of tissues
    • Climbers – Climbing plants and vines

Molles: Ecology 2nd Ed.

westoby et al
Westoby et.al.
  • Woody plants and climbers produced 10x the mass of seeds than either graminoids or forbs

Fig 12.7

Molles: Ecology 2nd Ed.

seed size and number in plants2
Seed Size and Number in Plants
  • Westoby et.al. recognized six seed dispersal strategies:
    • Unassisted – no specialized structures
    • Adhesion – hooks, spines, or barbs
    • Wind – wings, hair, (resistance structures)
    • Ant – oil surface coating (elaisome)
    • Vertebrate – fleshy coating (aril)
    • Scatterhoarded – gathered,stored in caches

Molles: Ecology 2nd Ed.

slide17

Fig 12.8

Molles: Ecology 2nd Ed.

seed size and number in plants a trade off
Seed Size and Number in PlantsA trade-off!
  • Small plants with many small seeds have advantage in areas of high disturbance
  • Plants with large seeds are constrained to producing fewer seedlings that are more capable of surviving env. hazards

Molles: Ecology 2nd Ed.

seed size and number in plants3
Seed Size and Number in Plants
  • Jakobsson and Eriksson – seed size variation explained many differences in recruitment success
    • Larger seeds produce larger seedlings and were associated with increased recruitment

Fig 12.10

Molles: Ecology 2nd Ed.

seed size and number in plants4
Seed Size and Number in Plants
  • Seiwa and Kikuzana – larger seeds produced taller seedlings
    • Energy reserve boosts seedling growth
    • Rapid growth helps seedling penetrate thick litter layer

Fig 12.11

Molles: Ecology 2nd Ed.

life history variation among species
Life History Variation Among Species
  • Shine and Charnov: 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

Molles: Ecology 2nd Ed.

slide22

Fig 12.12

Molles: Ecology 2nd Ed.

life history variation among species1
Life History Variation Among Species

Fig 12.12

  • Gunderson: clear relationship between adult fish mortality and age of repro. maturity
    • Species with higher mortality show higher relative reproductive rate

Molles: Ecology 2nd Ed.

life history classification
Life History Classification
  • MacArthur and Wilson
    • r selection: (per capita rate of increase) characteristic high population growth rate
    • K selection: (carrying capacity) characteristic efficient use of resources

Molles: Ecology 2nd Ed.

slide25
r - K
  • Pianka : r and K are ends of a continuum Most organisms are in-between
    • r selection: unpredictable environments
    • K selection: predictable environments

Molles: Ecology 2nd Ed.

r and k fundamental contrasts
r and K: Fundamental Contrasts
  • Intrinsic Rate of Increase:
    • Highest in r selected species
  • Competitive Ability:
    • Highest in K selected species
  • Reproduction:
    • r: numerous individuals rapidly produced
    • K: fewer larger individuals slowly produced

Molles: Ecology 2nd Ed.

plant life histories
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 dry matter production

Molles: Ecology 2nd Ed.

plant life histories1
Plant Life Histories
  • Four Environmental Extremes:
    • Low Disturbance : Low Stress
    • Low Disturbance : High Stress
    • High Disturbance : Low Stress
    • High Disturbance : High Stress

Molles: Ecology 2nd Ed.

plant life history strategies
Plant Life History Strategies
  • 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

Molles: Ecology 2nd Ed.

slide30

Fig 12.20

Molles: Ecology 2nd Ed.

slide31
Winemiller and Rose proposed new classification scheme based on age of reproductive maturity (a), juvenile survivorship (lx) and fecundity (mx)
    • Opportunistic: low lx – low mx – early a
    • Equilibrium: high lx – low mx – late a
    • Periodic: low lx – high mx – late a

Molles: Ecology 2nd Ed.

slide32

Fig 12.21

Molles: Ecology 2nd Ed.

slide33

Fig 12.22

Molles: Ecology 2nd Ed.

summary
Summary
  • Finite resources require trade-off between number and size of offspring; few larger offspring versus many smaller offspring
  • With low adult survival, organisms begin reproducing earlier and invest more energy into reproduction; when adult survival is higher, organisms defer reproduction to a later age and allocate less energy to reproduction
  • Life histories may be classified on basis of pop. characteristics such as mx, lx
  • + age maturity

Molles: Ecology 2nd Ed.