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1 Sign up for: IB Spotlight Send email to:

2 Ch 11: Population Growth + Regulation dN/dt = rN dN/dt = rN(K-N)/K
BRING to LECTURE: PRINT of Lecture Outline 2) Pg in Manual 2

3 Ch 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 to maximize fitness…

4 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 lifespan

5 A search for a set of rules when particular traits affecting reproduction and survival may be favored by natural selection.

6 Life history results from rules and choices influencing survival and reproduction.
Growth Longevity Maturity Parental care Juvenile survival Reproduction: 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?

7 Life histories vary along a slow-fast continuum.

8 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 traits

9 Lack: 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.

10 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.

11 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?)

12 Alternative pathways for resource allocation
Energy + matter growth reproduction maintenance immediate profit increased competitive ability From Barbour old book increased numbers increased survival delayed profit reproduction

13 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.

14 *** Describe, then explain this tradeoff: reproduction vs. mortality
C52.5 Cost of reproduction on survival

15 What is the tradeoff between:
parental investment vs. parental survival?

16 Explain the law of ‘diminishing returns’:
trade-off between fecundity vs. survival

17 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.

18 Major life history traits
1 Age of Maturity 2 Fecundity 3 Parity (# times reproduce) 4 Aging and lifespan

19 1) 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.

21 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 ages

22 Explain: 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 size

23 2) 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 species

24 Wide variation among organisms in life history traits.
temperate tropical

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 selection does this demonstrate? Directional Stabilizing Is genetic variation being maintained or reduced? Average Euroopean magpie clutch size of 7 was manipulated to make up clutches of The most productive clutch size was seven.

26 Explain: Adult lifespan determines optimal
allocation between growth and reproduction. Fish A Fish B e.g. indeterminate growth in fish (continue to grow throughout life; fecundity directly related to body size)

27 Summarize all graphs in one sentence.
Explain this evolutionary shift in life histories. (selection by predators on both adults and young occurs)

28 If indeterminate growth, Fecundity is related to body size;
Growth vs. Fecundity If indeterminate growth, Fecundity is related to body size; Increased fecundity in one year reduces growth, and thus fecundity, in future. Short-lived emphasize fecundity over growth High 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

29 3) Parity How many times to reproduce per lifetime? Semelparous (monocarpic) once Iteroparous (polycarpic) repeated

30 If semelparous, at what year to undergo ‘big-bang’ reproduction?
Annual Biennial Long-lived

31 Semelparity: Hypothesis: When preparation for reproduction is extremely costly?

32 Why 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

33 Semelparity: Hypotheses…
When payoff for reproduction is highly variable but favorable conditions are predictable? When pollinators attracted to massive display?

34 Iteroparity: When low current reproduction results in maintaining high future reproduction. Perennials… Repeated breeders…

35 4) Aging and Lifespan Senescence is a decline in physiological function with age. Causes decline in fecundity and survival

36 Strength of selection varies with mortality rate
Strength 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? 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.

37 Why 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.

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