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2. Ch 11: Population Growth + Regulation dN/dt = rN dN/dt = rN(K-N)/K
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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.