3Ch 7: Life Histories and Evolution Where put in survivorship curves?Where put in lxmx curve so can do homework?Lifetime scheduling of resources and time tomaximize fitness…
4Objectives Define life history Explain how related to evolution Resource allocation and tradeoffsCorrelated life history traits in contrasting environmentsExplain evolution of life history traitsAge of maturityFecundityParity (no. times reproduce/lifetime)Aging and lifespan
5A search for a set of rules when particular traits affecting reproduction and survival may be favored by natural selection.
6Life history results from rules and choices influencing survival and reproduction. GrowthLongevityMaturityParental careJuvenile survivalReproduction: a few large offspirng or many small?Adult survival: how much time to invest in parental care erus self-maintenance?Parity: How often to breed? How long to live? How fast to grow/develp?At what age and size to reproduce? When to undergo metamorphosis?Offspring: How fast to grow and develop? When to undergo metamorphosis?Maturity: At what age and size to reproduce?
8Traits are correlated in contrasting environments. Slow (often large organisms)slow developmentdelayed maturitylow fecundityhigh parental investment/offspringlow mortalitylong lifeFast: opposite traits
9Lack: life history in an evolutionary context. As life history traits contribute to reproductive success, they influence evolutionary fitness.Life histories vary consistently with environmental factors; hence may be molded by natural selection.
10Life history: schedule of organism’s life, including: age at first reproduction (maturity)number and size of offspring (fecundity)number of reproductive events (parity)aging (life span)The values of these traits are solutions to the problem of allocating limited time and resources among various structures, physiological functions, and behaviors.
11Resource AllocationOrganisms face a problem of allocation of scarce resources. (compromise? or can organisms increase overall performance without trading off one function against another?)
12Alternative pathways for resource allocation Energy + mattergrowthreproductionmaintenanceimmediateprofitincreasedcompetitiveabilityFrom Barbour old bookincreasednumbersincreasedsurvivaldelayedprofitreproduction
13Tradeoffs: Allocation of time, energy, or materials devoted to one structure or function cannot be allotted to another.Costs: Allocation to current reproduction involves tradeoff with survival, growth, and future reproduction.
14*** Describe, then explain this tradeoff: reproduction vs. mortality C52.5 Cost of reproduction on survival
15What is the tradeoff between: parental investment vs. parental survival?
16Explain the law of ‘diminishing returns’: trade-off between fecundity vs. survival
17Life histories balance trade-offs between current reproduction and future reproduction. Great variation among organisms in resolving the fundamental tradeoff between fecundity and adult growth and survival.Principle: limited time and resources are allocated among competing functions so as to maximize lifetime reproductive success.
18Major life history traits 1 Age of Maturity2 Fecundity3 Parity (# times reproduce)4 Aging and lifespan
191) Age of Maturity When should an organism begin to breed?
20*** Summarize the major result. What explains the pattern? Species with high adult survival mature later than those with low adult survival.
21What determines age of maturity? Affects generation time and rate of entry of genes into gene poolBenefit to not delay: immediate fecundityBenefit to delay: (if have relatively long lifespan) may have age-related gains in fecundity from growth or experienceBUT cost to delay:May have risk of mortality with timeMay have reduced fecundity at laterages
22Explain: Optimal age at maturity (i.e. maximize lifetime reproduction) variesin direct proportion to longevity (lifespan).e.g. determinate growth in a lizard: starts toreproduce after reaches maximum size
232) Fecundity: How many offspring per reproductive bout? Fecundity vs. parental investment/offspringseed size vs. seed numberegg size vs. egg numberGreat variation in seed and egg size among species
24Wide variation among organisms in life history traits. temperatetropical
25***Experimental test of hypothesis: Number of eggs per clutch is limited by food supply. Normal clutch size = 7. Do the data support the hypothesis?What type of selectiondoes this demonstrate?DirectionalStabilizingIs genetic variation beingmaintained or reduced?Average Euroopean magpie clutch size of 7 was manipulated to make up clutches of The most productive clutch size was seven.
26Explain: Adult lifespan determines optimal allocation between growth and reproduction.Fish AFish Be.g. indeterminate growth in fish(continue to grow throughout life;fecundity directly related to body size)
27Summarize all graphs in one sentence. Explain this evolutionary shift in life histories.(selection by predators on both adults andyoung occurs)
28If indeterminate growth, Fecundity is related to body size; Growth vs. FecundityIf indeterminate growth,Fecundity is related to body size;Increased fecundity in one year reducesgrowth, and thus fecundity, in future.Short-lived emphasize fecundity over growthHigh extrinsic adult mortality rates favor increased reproductive effort, or investment in offspring, at expense of adult survival and future reproduction.Long-lived emphasize growth over fecundity
293) ParityHow many times to reproduce per lifetime?Semelparous(monocarpic) onceIteroparous(polycarpic) repeated
30If semelparous, at what year to undergo ‘big-bang’ reproduction? AnnualBiennialLong-lived
31Semelparity: Hypothesis: When preparation for reproduction is extremely costly?
32Why is cicada: Semelparous? Synchronous? Semelparous: gives larvae time to grow to adulthood on diet of low nutritional quality(xylem of plant roots)Synchronous: satiate predators
33Semelparity: Hypotheses… When payoff for reproduction is highly variable but favorable conditions are predictable?When pollinators attracted to massive display?
34Iteroparity: When low current reproduction results in maintaining high future reproduction. Perennials… Repeated breeders…
354) Aging and LifespanSenescence is a decline in physiological function with age.Causes decline in fecundity and survival
36Strength of selection varies with mortality rate Strength of selection varies with mortality rate. If high mortality, few reach old agelittle selection for mechanisms to prolong life. Would green or orange have stronger selection to delay senescence?Strength of selection on changes in mortality and fecundity at a particular age is related to the proportion of individuals in the population alive at that age, which depends largely on rates of mortality caused by extrinsic factors earlier in life.In green, with lower survival rates, few individuals survive to aold age and there is little selection to delay senescence.In yellow with higher survival rates and an older age structure, greater hance of selection in changes in survival or fecundity.
37Why does aging vary?Not all organisms senesce at same rate, suggesting that aging may be subject to natural selection and evolutionary modification.Strength of selection diminishes on traits expressed at progressively later ages.