BIOS 3010: Ecology
Lecture 14: Life Histories:
•  Lecture summary:
–  Components of life
histories:
•  Growth.
•  Fecundity.
•  Survivorship.
Dendrobates, M & P. Fogden, Rainforests, A Celebration
–  Reproductive value.
–  Trade-offs.
–  r- and K-selection.
–  Habitat templates.
–  Clutch size.
Linnet, D. Attenborough (1998), Life of Birds, Princeton.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 14: slide 1
2. Components of life histories:
•  Growth, fecundity and survivorship
– (i) Growth
•  Balance between the benefits and costs of
large and small sized individuals:
– (Figs. 14.1 & 4.16).
•  Development
– Development can be varied independently of
growth.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 14: slide 2
3. Components of life histories:
•  (ii) Fecundity
–  Rapid development can lead to early reproduction
–  Timing important (pre-reproductive period length).
–  Duration and frequency of reproduction is also
important (semelparity and iteroparity).
•  Offspring size
–  variation in parental investment in individual offspring.
•  Number of offspring
–  variation in numbers.
•  Parental care
–  variation in how much parents look after offspring.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 14: slide 3
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4. Components of life histories:
•  (iii) Survivorship
– Variation in mortality, affected by:
•  Energy storage:
– Valuable for irregularly supplied resources.
– Dispersal in space and time:
•  Like migration across space and diapause
through time to escape periods of resource
shortage.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 14: slide 4
5. Reproductive effort:
•  Proportion of the available resource input that is
allocated to reproduction over a defined period of
time.
•  E.g., the allocation of energy or dry weight to different
parts at various stages of development (Fig. 14.3).
•  "Natural selection favours those individuals that make
the greatest proportionate contribution to the future of
the population to which they belong.
–  Begon et al., 2006, p 111.
–  Life histories are evolutionary attempts to maximize fecundity
and survival and these can be compared as a single "currency
»  The reproductive value as a measure of fitness
»  Such as the intrinsic rate of natural increase r, or the basic
reproductive rate Ro.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 14: slide 5
6. Reproductive value:
•  (i) Reproductive value at a stage or age is the
sum of the current reproductive output and the
future reproductive value.
•  (ii) Future reproductive value includes both
future survival and expected fecundity.
•  (iii) Future contribution of an individual is
determined relative to the contribution of others.
•  (iv) The life history favored by natural selection will
be the one with the highest sum of contemporary
output plus future output (Fig. 14.4).
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 14: slide 6
2
7. Trade-offs:
•  Life histories are balances of costs and
benefits:
–  One characteristic can result in increased
benefits that are associated with decreased
benefits from another characteristic
(Fig. 4.19 & Fig. 4.23).
–  This figure also shows the cost of
reproduction (Fig. 4.22).
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 14: slide 7
8. r and K selection:
•  After MacArthur & Wilson (1967) based on
parameters of the logistic equation:
–  r-selected individuals:
•  Favored for the ability to reproduce rapidly (high r values) in r-selecting habitats (more unstable).
–  K-selected individuals:
•  Favored for the ability to make a large proportional
contribution to a population which remains at its
carrying capacity (K) in K-selecting habitats (more
stable).
–  These are extremes of a continuum.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 14: slide 8
9. Characteristics of r and Kselected individuals:
Habitat:
Individual size:
Timing of reproduction:
Parity:
Reproductive allocation:
Number of offspring:
Size of offspring:
Parental care:
Survivorship investment
r-selected individuals
unstable, unpredictable
smaller
earlier
semelparous
higher
many
small
no
Low (little defense,
poor competitor)
K-selected individuals
stable, predictable
larger
later
iteroparous
lower
few
large
yes
High (good defense,
highly competitive)
See Figure 14.20 and Table 4.7
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 14: slide 9
3
10. Habitat and life history
•  Habitat is the templet (template) to which
individuals fit their life history (Southwood,
1977).
•  For example, guppies in Trinidad streams:
–  Selection by different fish predators influences the
cost of reproduction in guppies (Table 4.6) and
selects for:
•  Shift in offspring sizes.
•  Change in reproductive allocation.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 14: slide 10
11. Clutch size:
•  How many eggs should a bird lay?
•  “Lack clutch size”
–  Balance between number produced & subsequent
survival to maturity (Fig. 4.29).
–  Lack’s predictions not supported because:
•  (1) Inadequate assessment of offspring fitness:
–  Subsequent survival of added eggs not measured - so Lack
may be correct?
•  (2) Cost of reproduction (Fig 4.29) not considered:
–  Impact of present reproduction on future reproduction in
iteroparous species.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 14: slide 11
Figure 14.1 (3rd ed.): Larger female
crabs produce more offspring.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 14: slide 12
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Figure 4.16: Predicted male damselfly
size corresponds to population mode.
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 14: slide 13
BIOS 3010: Ecology
Lecture 14: slide 14
Figure 14.3
(3rd ed.):
Percentage
allocation of
calories to parts of
annual plants,
(a) Senecio,
(b) Chrysanthemum
(see Fig. 4.17 4th ed.)
Dr. S. Malcolm
Figure 14.4 (3rd ed.): Change in reproductive value
with age in (a) Phlox and (b) grey squirrels.
(see fig. 4.18, 4th ed.)
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 14: slide 15
5
Figure 4.19:
Life history tradeoffs in:
(a) migratory fruit
flies,
(b) douglas fir,
(c) male fruit flies
with 8 virgin, 1 virgin
+ 7 mated or 0 virgin
+ 8 mated females
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 14: slide 16
Figure 4.23: Trade-offs in (a) goldenrod spp.,
(b) Hawaiian fruit flies, (c) Sceloporus lizards
3 = Solidago canadensis
Predictable
pollen
Dr. S. Malcolm
Leaf
bacteria
BIOS 3010: Ecology
Unpredictable
yeast
Lecture 14: slide 17
Figure 4.22: Cost of reproduction
in Senecio (deaths above line)
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 14: slide 18
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Figure 14.20 (3rd ed.):
Plants and the r/K
continuum:
(a) Reproductive allocation
(b) Seed weight
(c) age of reproduction
variation with life span
(see fig 4.30, 4th ed.)
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 14: slide 19
Table 4.7:
(North Dakota)
Dr. S. Malcolm
BIOS 3010: Ecology
(Texas)
Lecture 14: slide 20
Table 4.6:
Large fish
predator
Dr. S. Malcolm
Small fish
predator
BIOS 3010: Ecology
Lecture 14: slide 21
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Figure 4.29: Lack clutch size (a) prediction based
on offspring fitness trade-off, (b) inclusion of cost of
reproduction and maximum net benefit
Dr. S. Malcolm
BIOS 3010: Ecology
Lecture 14: slide 22
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