1. LIFE HISTORIES
Chapter 12
Molles: Ecology 2nd Ed.

2. few larger offspring vs. many smaller offspring
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.

3. 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.

4. 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.

5. 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.

6. Why these 15 darter species?
Variation in life history
Variation in body size ( mm)
Variation in egg size ( mm)
Variation in number of eggs ( )
Molles: Ecology 2nd Ed.

7. Molles: Ecology 2nd Ed.

8. Darters:
Molles: Ecology 2nd Ed.

9. 1. Big darters produce more eggs that are smaller:
Turner + Trexler
1. Big darters produce more eggs that are smaller:
Molles: Ecology 2nd Ed.

10. Less dispersion = greater isolation = rapid gene differentiation
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.

11. Look at proteins (or DNA sequence) Variation in proteins (size, shape)
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.

12. Fig 12.5
Molles: Ecology 2nd Ed.

13. Seed Size and Number in Plants
Many families produce small # of large seeds
Dispersal mode might influence seed size
Molles: Ecology 2nd Ed.

14. 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.

15. 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.

16. 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.

17. Fig 12.8
Molles: Ecology 2nd Ed.

18. Seed Size and Number in Plants A 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.

19. 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.

20. 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.

21. 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.

22. Fig 12.12
Molles: Ecology 2nd Ed.

23. Life History Variation Among Species
Gunderson: clear relationship between adult fish mortality and age of repro. maturity
Species with higher mortality show higher relative reproductive rate
Fig 12.12
Molles: Ecology 2nd Ed.

24. 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.

25. Pianka : r and K are ends of a continuum Most organisms are in-between
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.

26. 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.

27. Intensity of disturbance:
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.

28. Four Environmental Extremes: Low Disturbance : Low Stress
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.

29. 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.

30. Fig 12.20
Molles: Ecology 2nd Ed.

31. Opportunistic: low lx – low mx – early a
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.

32. Fig 12.21
Molles: Ecology 2nd Ed.

33. Fig 12.22
Molles: Ecology 2nd Ed.

34. 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.

35. Molles: Ecology 2nd Ed.