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Terrestrial Ecology
Zoological Part
2004
Who is who?
• Koos Boomsma
• Michael Poulsen
• Daniel Kronauer
What’s up for these two weeks?
• Exiting Evolutionary Ecology
• A further confrontation with the hardship of
science
• Straightforward textbook chapters versus…
• ….recent (mostly) case studies of varying
complexity
• Hot issues: Ageing, natural (social) conflicts,
infectious diseases (AIDS), conservation
The Issues
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•
•
•
Life Histories and Phenotypic Plasticity
Conflict and Cooperation
Parasites and Diseases
Metapopulations and Conservation
Life Histories and Phenotypic
Plasticity
Investments in and Timing of Growth and Reproduction
Broad Scale Life-history Correlations
Pregnancy Duration versus Body Size
Offspring
independent
Offspring
carried
May & Rubenstein, 1984
Offspring kept
In the nest
Clutton-Brock, 1991
Broad Scale Life-history Correlations
Maximal Life Span versus Body Size
Not the slopes but the level is interesting
Stearns, 1992
Prothero & Jürgens, 1992
Life Span is Tremendously Variable
274 Species of Invertebrates
170 Mammal Species in Zoos
Stearns, 1992
Stearns, 1992
Comfort, 1979
Eisenberg, 1981
Broad Scale Life-history Correlations
Egg Volume versus Body Size
.
Residuals Contain the Important Information
Blueweiss et al., 1978
Clutton-Brock, 1991
The Comparative Method
The Statistical Analysis of Comparative (Across Taxa)
Life History Data
But now ........ To the Explanations (Life History Theory)
Trade-off curves
Convex
Concave
Actual fitness contours
Iteroparity
Annual Semelparity
Option Sets
14.10
Plots May also be the Other Way
Around
Survival instead of Growth
Trade-off Curves May
also be Complex
Stearns, 1976, 1992
Cole’s Paradox – Why is Iteroparity
so Common?
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•
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•
Let Ba = # offspring Annual
Let Bp = # offspring Perennial (Iteroparous)
Annuals: Nt+1 = erNt = BaNt  lnBa = r
Perennials: Nt+1 = erNt = BpNt + Nt =
(Bp + 1)Nt  ln(Bp + 1) = r
• The fitness of these two reproductive types is
equal when: Ba = Bp + 1.
• ????? Annuals need to reproduce only marginally
more to be selected for
Cole’s Paradox – Why is Iteroparity
so Common?
• The Paradox was solved by including agespecific survival rates: pjuv (juveniles) and pad
(adults)
• Now the fitness of these two reproductive
types is equal when:
pad
Ba  Bp 
p juv
• Conclusion: Because pad >> pjuv in many
populations, it is often best to be iteroparous
• See Compendium for Details
The
Cost
of
Reproduction
Trade-off
Offspring Size versus Offspring #
clear
unclear
14.11
High CR
Lobelia’s on Mt. Kenia
14.17
Problems in the Measurement of
Trade-offs
Survival
A=R+S
Var A >> Var B
Fraction to R
Var A << Var B
Reproduction
Trade-offs (genetic correlations) may be invisible in the field
Stearns, 1992
Clutch Size Optimisation
Assume a single optimal egg size
Lack’s optimal clutch size
Iteroparous organisms need reserves to buffer the cost of
reproduction and to minimise the temporal variation in
reproductive performance
Clutch Size Optimisation
Large SD means
large Temporal
variation in Fitness
Geometric mean fitness is often a better measure than arithmetic
n
mean fitness
√Y1.Y2.Y3.Y4.....Yn
Boyce & Perrins, 1987
Cockburn, 1991
Clutch Size Optimisation
Other factors also play a decisive role: Laying date
14.24
Model Predictions Match Observations in the Field
Clutch size is a phenotypically plastic life-history trait
Daan et al., 1990
Krebs & Davies, 1991
Size and Age at Maturity
% Female Biomass
 Reproduction
Table 14.1
3 Streams with Different Predation Risk
C = High Adult Pr.
R = Moderate Juv. Pr.
A = Low Predation
R: Size & Age at
Maturity 
C: Reproductive
Effort 
R&C: Body Size ↓
A transplantation experiment reproduced these patterns
in 11 years (30-60 generations)
Reznick & Endler, 1982
Cockburn, 1991
Size and Age at Maturity
14.27
Comparative data corrected for body size
Reproductive Value
Phlox drummondii
14.16
cf. 14.4
Age at maturity
Cockburn, 1991
Life Span
= Constant
Age at Maturity
But only within taxa
Charnov & Berrigan, 1991
Sex ratio
• Should be measured in terms of investment
• Is often but far from always 50:50 at the end
of parental investment
• The equilibrium ESS sex ratio is independent
of an XX/XY sex chromosome system
• Adult sex ratios may be very skewed owing
to sex specific mortality or mating success
• Is often skewed in haplo-diploid parasitoids
and social insects (ants, bees, wasps)
• See Compendium for Details
Only females in their prime age
can reproduce each year
Male calfs are usually more ”expensive”
Clutton-Brock, 1984, 1991
Clutton-Brock, 1981, 1991
Sex ratio and Cost of Reproduction
Sex ratio and Cost of Reproduction
Sons
b,c,d: sons are more expensive
a: daughters are more expensive
Daughters
A paper on human twins of different sex
Clutton-Brock et al., 1982
Why does almost every
multicellular organism senesce?
• Germ-line and Soma are separated
• Soma is disposable if that serves the
fitness of the germ-line
• Selection does not remove deleterious
mutations expressed late in life
• Selection favors mutations that are
beneficial early in life, even if they are bad
later in life
The Optimal Repair Model
Excess Repair is not Favoured by Selection
3 papers this afternoon
Kirkwood, 1985
Stearns., 1992
Phenotypic Plasticity
Reaction norms of isofemale lines
Differences in slopes are particularly important
because this genetic variation is easy to maintain
Reaction Norm Theory
Size and Age at Maturity
Stearns, 1989, 1992
Reproductive Effort versus Survival
Practical Examples
Good Nutrition
Bad Nutrition
14.22
Drosophila mercatorum
Gebhardt & Stearns, 1988; Stearns, 1992
Human females
Stearns & Koella, 1986; Stearns, 1992
Summary
• Life-history traits are heritable, but usually in a
phenotypically plastic way
• Many key aspects of life are determined by
selection on life-history traits
• Reproduction is costly and has a carefully
balanced, but context dependent, economy
• In plants, animals, (microorganisms), and humans
• 3 papers on ageing and 1 on early growth effects