LIFE HISTORIES

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

2. 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 Fish • Fish 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 (44 - 127 mm) • Variation in egg size (0.9 - 2.3 mm) • Variation in number of eggs (49 - 397) Molles: Ecology 2nd Ed.

7. Molles: Ecology 2nd Ed.

8. Darters: Molles: Ecology 2nd Ed.

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

10. 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. Gene flow? • Look at proteins (or DNA) • 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 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.

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 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.

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. 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. 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. 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. 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.