Life History
Life history - An organism's life history is its lifetime pattern of growth,
differentiation, storage of energy and most importantly, its
reproduction.
Life Histories vary among species
Life history variation in plants has to do with the lifespan and how many
times it will reproduce.
annuals-
Go from seed to seed in less than 12 months. Life cycle is
competed in one growing season.
biennials – 1) a season of vegetative growth and storage of
photosynthate in the roots followed 2) by a season of
reproductive output –flowers  seed.
perennials - Live for more than two years, reproduce for many years.
Life Histories vary among species
A century plant
– Grows for many seasons
– Reproduces in 10-30 years
– Reproduces only once
Annual
Biennial
Perennial
Life Histories vary among species
A dandelion
– Germinates and grows one season.
– Continues to grow the next season.
– Reproduces once.
Annual
Biennial
Perennial
Life Histories vary among species
Broccoli
– Germinates and grows in one season.
– Reproduces once.
Annual
Biennial
Perennial
Life Histories vary among species
An oak tree
- Germinates and grows
many seasons
- Reproduces many times
Annual
Biennial
Perennial
http://sptreefarm.com/interesting-facts-about-live-oak-trees.html
Life Histories vary among species
Animals do not have well-defined growth periods like plants.
“big-bang”
reproduction
1-8 years in the ocean
http://www.tutorvista.com/science/external-fertilization
Life Histories vary among species
Red kangaroos can simultaneously care for 3 young at once.
Joey in pouch, 7-9
months
A baby on a teat
Joey out of pouch
http://www.duskyswondersite.com/tag/kan
garoo-nursing/
http://worldanimalspic.blogspot.com/2013/10/australian-kangaroo.html
http://www.dailymail.co.uk/
Life Histories vary among species
Reproductive periodicity
Semelparous - semel – once; parous – bearing, producing
Iteroparous - itero – repeat; parous – bearing, producing
Reproductive Value
Vx is the contribution an average individual aged x will make to the next
generation before it dies.
𝑤
𝑉𝑥 = 𝑏𝑥 +
𝑡=𝑥+1
𝑙𝑡
𝑏𝑡
𝑙𝑥
t and x - age
w – age at last reproduction
Reproductive Value
Reproductive value of the annual Phlox drummondii.
Age Classes – The year during which this annual lives has been divided up into 12 age classes that
are not uniform in time.
lx – is age-specific survivorship from a life table
bx – is age-specific birth rate from a life table
RRV – the Residual Reproductive value is
Reproductive Value
Reproductive Value
Age Class
1
2
3
4
5
6
7
8
9
10
11
12
13
Days
0-63
63-124
124-184
184-215
215-264
264-278
278-292
292-306
306-320
320-334
334-348
348-362
362-
lx
1.000
0.671
0.296
0.191
0.177
0.173
0.168
0.160
0.155
0.148
0.105
0.022
0.000
bx
0
0
0
0
0
0
0
0.330
3.130
5.420
9.260
4.310
0
RRV
2.407
3.588
8.133
12.603
13.600
13.915
14.329
14.715
12.060
7.210
0.903
0.000
0.000
Vx
2.407
3.588
8.133
12.603
13.600
13.915
14.329
15.045
15.190
12.630
10.163
4.310
0.000
Reproductive Value – graphically
Reproductive Value of
Phlox drummondii
30
25
Reproductive Value
bx (Current Reproduction)
Vx
20
RRV
15
10
5
0
0
2
4
6
8
Age Class
10
12
14
Reproductive Value – in words
• Phlox drummondii slowly increases Vx with age, then declines.
•
Vx is low for young individuals when they have only a low probability of surviving to
reproductive maturity.
• If survivorship of young plants is low, there is less benefit from reproduction and selection
favors a lower Vx at a young age
•
Recall trade-offs; reproduce a little, or survive and reproduce a lot later. Therefore, high
juvenile mortality increases RRV. The probability of reproducing in the future is greater.
•
BUT –only if it brings with it either an improvement of survivorship of young plants or a
compensatory increase in adult longevity and probability of future reproduction.
•
Vx steadily increases as the age of first reproduction is approached. It becomes more and
more certain that surviving individuals will reach reproductive maturity.
•
Vx is low again for older individuals because of reproductive opportunities left behind and
declines in fecundity or survival.
Reproductive Value – Pediculus humanus
For organisms that breed only once – T = average time from egg to egg.
For repeated reproducers - T = mean generation time: the average parental age at which all offspring are born.
Reproductive Value
Isle of Rhum
Reproductive Value
• Phlox drummondii slowly increases Vx with age, then
declines.
• Vx is low for young individuals when probability of
surviving to reproductive maturity is low.
• If survivorship of young plants is low, there is less benefit
from reproduction and selection favors a lower Vx at a
young age
• but only if it brings with it either an improvement of
survivorship of young plants or a compensatory increase
in adult longevity and probability of future reproduction.
• Vx steadily increases as the age of first reproduction is
approached. It becomes more and more certain that
surviving individuals will reach reproductive maturity.
• Vx is low again for older individuals because of
reproductive opportunities left behind and declines in
fecundity or survival.
Reproductive Value
Acacia suaveolens
• When the extrinsic death rate (death independent of
reproduction) for older plants is high compared to young
plants, then the number of reproductive attempts is
limited.
• Earlier reproduction is selected for, since any plant that
waits to reproduce at the expense of current production
is likely to have fewer offspring than those that don't.
• High adult mortality lowers RRV- the probability of
reproducing in the future is reduced.
Reproductive Value – why Vx is not maximized
Tradeoffs in the demand for photosynthate.
Pseudotsuga menziesii - Trade-off between growth and reproduction.
Reproductive Value - why Vx is not maximized all the time
Tradeoffs in the demand for photosynthate.
Poa annua – tradeoff between current and future reproduction.
Reproductive Value
Life History Traits of Plants
I did not cover
these traits in
lecture.