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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.

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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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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.

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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.

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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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Seed Size and Number in Plants

• Many families produce small number of larger seeds. Dispersal mode might influence seed size.

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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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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.

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• 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?

http://fish.dnr.cornell.edu/nyfish/Cyprinodontidae/mummichog.jpg

http://aquanic.org/images/photos/ingvar/Roughy.gif

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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.

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r K

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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.

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Plant Life Histories

• Four Environmental Extremes: Low Disturbance : Low Stress Low Disturbance : High Stress High Disturbance : Low Stress High Disturbance : High Stress

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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.

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Grime’s Plant Life History Triangle

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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

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Opportunistic, Equilibrium,and Periodic Life Histories

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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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Reproductive Effort, Offspring Size, and Benefit-Cost Ratios