Sign up for: IB Spotlight Send email to: [email protected] 11: Population Growth + Regulation dN/dt = rN dN/dt = rN(K-N)/KCh 7: Life Histories and EvolutionObjectivesA search for a set of rules when particular traits affecting reproduction and survival may be favored by natural selection.Life history results from rules and choices influencing survival and reproduction.Life histories vary along a slow-fast continuum.Traits are correlated in contrasting environments.Lack: life history in an evolutionary context.Life history: schedule of organism’s life, including:Resource AllocationAlternative pathways for resource allocationSlide 13*** Describe, then explain this tradeoff: reproduction vs. mortalitySlide 15Slide 16Slide 17Major life history traits1) Age of Maturity When should an organism begin to breed?*** Summarize the major result. What explains the pattern?What determines age of maturity?Slide 222) Fecundity: How many offspring per reproductive bout?Wide variation among organisms in life history traits.***Experimental test of hypothesis: Number of eggs per clutch is limited by food supply. Normal clutch size = 7. Do the data support the hypothesis?Slide 26Slide 27Slide 283) ParityIf semelparous, at what year to undergo ‘big-bang’ reproduction?Semelparity: Hypothesis: When preparation for reproduction is extremely costly?Slide 32Slide 33Iteroparity: When low current reproduction results in maintaining high future reproduction. Perennials… Repeated breeders…4) Aging and LifespanStrength of selection varies with mortality rate. If high mortality, few reach old agelittle selection for mechanisms to prolong life. Would green or orange have stronger selection to delay senescence?Why does aging vary?Sign up for:IB SpotlightSend email to:[email protected] 11: Population Growth + Regulation dN/dt = rN dN/dt = rN(K-N)/KBRING toLECTURE:1) PRINT ofLecture Outline2) Pg. 217-20 in ManualCh 7: Life Histories and EvolutionLifetime scheduling of resources and time to maximize fitness…Objectives•Define life history•Explain how related to evolution•Resource allocation and tradeoffs•Correlated life history traits in contrasting environments•Explain evolution of life history traits• Age of maturity• Fecundity• Parity (no. times reproduce/lifetime)• Aging and lifespanA search for a set of rules when particular traits affecting reproduction and survival may be favored by natural selection.Life history results from rules and choices influencing survival and reproduction.Juvenile survivalGrowthMaturityParental careLongevityLife histories vary along a slow-fast continuum.Traits are correlated in contrasting environments.•Slow (often large organisms)• slow development• delayed maturity• low fecundity• high parental investment/offspring• low mortality• long life•Fast: opposite traitsLack: 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.Life 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.Resource Allocation•Organisms face a problem of allocation of scarce resources. (compromise? or can organisms increase overall performance without trading off one function against another?)Alternative pathways for resource allocationgrowthreproduction maintenanceEnergy + matterreproductionincreased survivalincreasedcompetitive abilityimmediateprofitdelayed profitincreasednumbers•Tradeoffs: 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.*** Describe, then explain this tradeoff: reproduction vs. mortalityWhat is the tradeoff between:parental investment vs. parental survival?Explain the law of ‘diminishing returns’: trade-off between fecundity vs. survival•Life 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.Major life history traits•1 Age of Maturity•2 Fecundity•3 Parity (# times reproduce)•4 Aging and lifespan1) Age of Maturity When should an organism begin to breed?*** Summarize the major result.What explains the pattern?What determines age of maturity? •Affects generation time and rate of entry of genes into gene pool•Benefit to not delay: immediate fecundity•Benefit to delay: (if have relatively long lifespan)  may have age-related gains in fecundity from growth or experience•BUT cost to delay:• May have risk of mortality with time • May have reduced fecundity at later agesExplain: Optimal age at maturity (i.e. maximize lifetime reproduction) varies in direct proportion to longevity (lifespan).e.g. determinate growth in a lizard: starts to reproduce after reaches maximum size2) Fecundity: How many offspring per reproductive bout?•Fecundity vs. parental investment/offspring• seed size vs. seed number• egg size vs. egg number•Great variation in seed and egg size among speciesWide variation among organisms in life history traits.temperate tropical***Experimental test of hypothesis:Number of eggs per clutch is limited byfood supply. Normal clutch size = 7.Do the data support the hypothesis?What type of selectiondoes this demonstrate?a. Directionalb. StabilizingIs genetic variation beingmaintained or reduced?e.g. indeterminate growth in fish (continue to grow throughout life; fecundity directly related to body size) Explain: Adult lifespan determines optimalallocation between growth and reproduction.Fish AFish BSummarize all graphs in one sentence.Explain this evolutionary shift in life histories.(selection by predators on both adults and young occurs)Growth vs. Fecundity•If indeterminate