Life Histories

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

2. 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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6. 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.

7. 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.

8. 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.

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

11. 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.

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13. 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.

14. http://fish.dnr.cornell.edu/nyfish/Cyprinodontidae/mummichog.jpghttp://fish.dnr.cornell.edu/nyfish/Cyprinodontidae/mummichog.jpg http://aquanic.org/images/photos/ingvar/Roughy.gif • 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?

15. 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.

16. r K

17. 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.

18. Plant Life Histories • Four Environmental Extremes: • Low Disturbance : Low Stress • Low Disturbance : High Stress • High Disturbance : Low Stress • High Disturbance : High Stress

19. 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.

20. Grime’s Plant Life History Triangle

21. 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

22. Opportunistic, Equilibrium,and Periodic Life Histories

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28. 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.

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30. Reproductive Effort, Offspring Size, and Benefit-Cost Ratios