life history = ‘stages’ of life for an organism

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Life History = ‘stages’ of life for an organism. Number of offspring? How many usually survive? When do young mature (i.e. capable of reproduction)? How does environment affect these traits? What makes these traits adaptive?. Offspring Number Versus Offspring Size. - PowerPoint PPT Presentation

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  • Life History = stages of life for an organismNumber of offspring?How many usually survive?When do young mature (i.e. capable of reproduction)?How does environment affect these traits?What makes these traits adaptive?

  • Offspring Number Versus Offspring SizePrinciple of Allocation: energy for one function reduces energy available for other functions.Leads to trade-offs b/n number and size of offspring.Which one do you suppose produces more offspring?If theres an option, why one over the other???

  • Offspring size may be adapted to successful dispersaltake plantsWestoby et al. recognized 6 seed dispersal strategies:Unassisted: No specialized structures.Wind: Wings, hair, (resistance structures).Adhesion: Hooks, spines, or barbs.Ant: Oil surface coating (elaisome).Vertebrate: Fleshy coating (aril).Scatterhoarded: Gathered, stored in caches.

    Now were getting somewhere

  • Seed size is also related to growth formWestoby et al. recognized 4 plant forms:Graminoids: Grass and grass-like plants.Forbs: Herbaceous, non-graminoids.Woody Plants: Woody thickening of tissues.Climbers: Climbing plants and vines.Woody plant and climbers produced 10x the mass of seeds than either graminoids or forbs.Any thoughts on why?

  • Different plant forms adapted to different environmental conditionsSmall, large #s of seeds = advantage in disturbed areas = rapid colonization.Large, fewer seeds capable of withstanding hazardscompeting with established plantsdealing with shadedefoliationnutrient shortagedrought

  • Life History = stages of life for an organismNumber of offspring?How long do they live?When do young mature (i.e. become capable of reproduction)?How does environment affect these traits?What makes these traits adaptive?

  • Age of Reproductive MaturityKey factors:Survivorship how long do organisms live?not long = reproduce fastlong time = wait to reproducebut why wait?Energy/time needed for growthMust grow to reproduceBigger organisms = bigger energy budget = more energy to survive = smaller proportion of energy required to reproduceReproductive effort = allocation of energy to production/caring for offspring

  • Age of Reproductive MaturityIn general, high adult mortality (low survivorship) = early reproductive maturityMore energy devoted to reproductionGreat reproductive effortLow adult mortality (high survivorship) = delayed maturityMore energy to growth and survivalLower reproductive effortLets look at an example

  • Pumpkinseed sunfish reproductive effort depends on survivorshipPopulations with relatively low adult survival = more reproductive effort.High adult survival = less reproductive effortHow does one measure reproductive effort?Look at the size of their gonads (for one)! Gonadosomatic index (GSI) = ovary size/body size *100

  • Life History = stages of life for an organismNumber of offspring?How many usually survive?When do young mature (i.e. capable of reproduction)?How does environment affect these traits?What makes these traits adaptive?

  • Life History Classification old schoolMacArthur and Wilson 1967r selection (per capita rate of increase)Selected for high population growth rate.Colonizers of new/disturbed habitat.Maximize r; type III survivorshipK selection (carrying capacity)Efficient resource use/highly competitive.Maintain population near K; type I or II

  • r and K: Fundamental Contrastsr and K = ends of continuum, most organisms are in-between.r selection: Unpredictable environments.K selection: Predictable environments.

  • Plant Life Historiesslightly newer schoolGrime 1977: 2 important variables in plant life history:

    Intensity of disturbance:Destruction of biomass.Intensity of stress:External constraints limiting growth.Four Environmental Extremes:Low Disturbance : Low StressLow Disturbance : High StressHigh Disturbance : Low StressHigh Disturbance : High Stress

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

  • Offspring size can influence dispersal(dispersal influences evolution)Darters follow the pattern: many small eggs to fewer large eggsDarter pops. w/ many small eggs = less genetic difference than those with fewer, larger eggs (Turner and Trexler, 1998).Larger eggs hatch/feed earlier, dont drift or disperse as far.Greater isolation = rapid gene differentiation.Offspring size has evolutionary consequences!

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