Life history characteristics

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Life history characteristics
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Organisms face fundamental trade-offs in their
use of energy and time Changes in life history
are caused by changes in the allocation of energy
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Life history parameters
Number size of offspring Age distribution of
reproduction Life span
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Number size of offspring
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Number size of offspring
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Age distribution of reproduction
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Life span
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tuna -many small eggs -grow quickly, reproduce
young -reproduce daily dogshark -few large
eggs -grow slowly, reproduce after 25
years -reproduce every few years
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Number size of offspring Age distribution of
reproduction Life span
Differences in these parameters affect growth
rate (fitness)
overlapping generations discrete generations
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Life history parameters
t time (days or years) x age of an
individual (days or years) lx proportion of
newly laid eggs that survive to age x mx
expected of offspring (fecundity) a age at
first reproduction z age at last
reproduction r growth in population size per
female per unit time
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Life history parameter conclusions
increased lx will increase r increased mx will
increase r offspring produced earlier contribute
more to population growth earlier reproduction
begins, greater r
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Life history parameter characteristics
Characteristics that would maximize r
(fitness) higher survival through reproductive
ages higher fecundity at each reproductive
age higher fecundity especially early in
life longer reproductive lifespan earlier age
of first reproductive
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Constraints phylogenetic genetic physiological
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Trouble with tribbles
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Life history parameters
Number size of offspring Age distribution of
reproduction Life span
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Lacks hypothesis
selection will favor the clutch size that
produces the most surviving offspring
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Lacks hypothesis
assumes no trade-off between a parents
reproductive effort 1 year and its survival or
reproductive performance in future years
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Lacks hypothesis
assumes only effect of clutch size on offspring
is in determining whether the offspring survive
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Lacks hypothesis
selection will favor the clutch size that
produces the most surviving offspring Assumptions
assumes no trade-off between a parents
reproductive effort 1 year and its survival or
reproductive performance in future years assumes
only effect of clutch size on offspring is in
determining whether the offspring survive
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Lacks hypothesis
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Organisms face a trade-off between making many
low-quality offspring or a few high-quality
offspring
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Size number trade off
fish
insects
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Optimum size number compromise
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Selection on parents favors a compromise between
the quality and quantity of offspring, but
selection on individual offspring favors high
quality
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Life history parameters
Number size of offspring Age distribution of
reproduction Life span
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In populations where mortality rates are high,
individuals tend to breed earlier in
life However, a trade-off exists between
reproductive effort early in life and
reproductive success late in life
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Life history parameters
Number size of offspring Age distribution of
reproduction Life span
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Semelparity iteroparity
Semelparity -population growth rate is
high -juvenile survival is high -adult survival
is low Iteroparity -population growth rate is
low -juvenile survival is low -adult survival is
high
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semelparity single reproductive event Pacific
salmon iteroparity multiple reproductive
events Atlantic salmon
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Male reproductive success alternative mating
tactics sneaker males sequential
hermaphroditism protandry protogeny
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Sequential hermaphroditism
protandry
protogeny
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Sequential hermaphroditism
protandry
protogeny
no change
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When mates are not monogamous, the life history
strategy that is optimal for one sex may be
suboptimal for the other
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Aging
Aging late life decline in an individuals
fertility and probability of survival
Why does aging persist? Rate of living theory -
accumulation of irreparable damage to
tissue Evolutionary theory - failure of
organisms to completely repair damage
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Aging
Rate of living theory - accumulation of
irreparable damage to tissue
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Aging
telomerase
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Aging
Evolutionary theory - failure of organisms to
completely repair damage -deleterious
mutations -trade-offs between repair and
reproduction
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Aging
Wildtype first reproduction 3, death 16
Lifetime reproductive success 2.419
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Aging
Mutation first reproduction 3, death 14
Lifetime reproductive success 2.340
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Aging
Mutation first reproduction 2, death 10
Lifetime reproductive success 2.663
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Aging
Because natural selection is weaker late in life,
alleles that enhance early-life reproduction may
be favored even if they also hasten death Also,
alleles that cause aging are only mildly
deleterious