Life Histories Chapter 12 Adaptation of an organism

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

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. v Leads to trade-offs between functions such as number and size of offspring. 2 2

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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. 6 6

Seed Size and Number in Plants • Jakobsson and Eriksson found seed size variation explained many differences in recruitment success. v Larger seeds produce larger seedlings and were associated with increased recruitment. 7 7

Seed Size and Number in Plants • Seiwa and Kikuzana found larger seeds produced taller seedlings. v Energy reserve boosts seedling growth. § Rapid growth helps seedling penetrate thick litter layer. 8 8

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

Life History Variation Among Species • Shine and Charnov pointed out vertebrate energy budgets are different before and after sexual maturity. v Before - maintenance or growth. v After - maintenance, growth, or reproduction. v Individuals delaying reproduction will grow faster and reach a larger size. § Increased reproduction rate. 11 11

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• Life History Variation Among Species Gunderson found clear relationship between adult fish mortality and age of reproductive maturity. v Species with higher mortality show higher relative reproductive rate. 13 13

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

Life History Classification • • Mac. Arthur and Wilson v r selection (per capita rate of increase) § Characteristic high population growth rate. v K selection (carrying capacity) § Characteristic efficient resource use. Pianka : r and K are ends of a continuum, while most organisms are in-between. v r selection: Unpredictable environments. v K selection: Predictable environments. 15 15

r K 16 16

Plant Life Histories • Grime proposed two most important variables exerting selective pressures in plants: v Intensity of disturbance: § Any process limiting plants by destroying biomass. v Intensity of stress: § External constraints limiting rate of biomass production. 17 17

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

Plant Life Histories • • • Ruderals (highly disturbed habitats) v Grow rapidly and produce seeds quickly. Stress-Tolerant (high stress - no disturbance) v Grow slowly - conserve resources. Competitive (low disturbance low stress) v Grow well, but eventually compete with others for resources. 19 19

Grime’s Plant Life History Triangle 20 20

Opportunistic, Equilibrium, and Periodic Life Histories • Winemiller and Rose proposed new classification scheme based on: v juvenile survivorship (lx), v fecundity (mx), and v age of reproductive maturity (α) Opportunistic: v Equilibrium: v Periodic: v low lx - low mx - early α high lx - low mx - late α low lx - high mx - late α 21 21

Opportunistic, Equilibrium, and Periodic Life Histories 22 22

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Reproductive Effort, Offspring Size, and Benefit-Cost Ratios • Charnov developed a new approach to life history classification. v 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. 28 28

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