Transcript Organism Life Histories

Organism
Life Histories
BIOL400
9 November 2015
Energy Allocation
 An
organism assimilates a finite amount of
energy, which it can devote to:




Growth
Reproduction
Tissue maintenance
Storage for later (see above)
Fitness
 Measure
of survival likelihood and
reproductive output
 Natural selection, based on the physical
and biotic environment, determines the life
history a species has

The one that maximizes fitness
Fig. 2.8 p. 25

Selection for
optimum
clutch size of
11 in blue
tits
Fig. 2.9 p. 25

Experimental
demonstration
that selection
has not
optimized
clutch size in
the house wren
(unless there is
a life-history
trade-off…)
Key Life-History Attributes
 Growth
rate
 Age at maturity
 Size at maturity
 Reproductive frequency


Annual
Lifetime
 Fecundity
 Propagule
size
Life-History Trade-Offs
 Stearns:
“Linkages between traits that
constrain the simultaneous evolution of
two or more traits”
 Increased allocation toward A decreases
possible allocation toward B
Present Reproduction vs.
Survival and
Future Reproduction
Present Reproduction vs.
Survival and
Future Reproduction

House wren??
 Red deer
 Kenyan Lobelia
 Beech trees
Fig. 2.9 p. 25
Fig. 8.20 p. 137
Fig. 8.19 p. 136
HANDOUT
Maturation age vs. fecundity
and/or propagule size
and survival
HANDOUT
Egg Size vs. Clutch Size
 Trade-off
may select for point at which
increasing clutch size leads to lower
fitness by reducing offspring size, and
increasing offspring size leads to lower
fitness by reducing clutch size
 Hence, an optimal egg size
Optimal Egg Size
Vs.
Anatomical Constraints on Egg Size
 If
selection optimizes egg size, egg size
should not correlate with female body size
 However, anatomical contraints may
cause eggs of small females to be smaller
than optimum

Egg size increases with female body size
HANDOUT
Congdon and Gibbons 1987
HANDOUT—Doughty 1997
Human Menopause
 Trading
off future reproduction and its
increased risks against helping of
grandchildren?
Life-History
Invariants
Life-History Invariants
 Invariant


…
…ratios (“dimensionless numbers”)
…X-Y relationships with set slopes
 Demonstrate
trade-offs
the nature of life-history
HANDOUTS—Charnov 1993
Genotype and Phenotype
 Is
variation in life history…
…genetic (induced by DNA)?
…phenotypic (induced by environment)?
Fig. 6.11 p. 91
Yarrow

Common-garden experiments demonstrate genotypic
effect—adaptation to local conditions?

All grown in identical greenhouse conditions
Reaction Norm
 Stearns’
definition: "The mapping of the
genotype onto the phenotype as a function
of the environment—expressed as a plot
of phenotypic values [Y] against
environmental values [X]. The reaction
norm of a genotype is the full set of
phenotypes that the genotype will express
in interaction with the full set of
environments in which it can survive."
Countergradient Variation
 Seemingly
good evidence that much of the
variation in organism life histories must be
genetic and adaptive
 Genetic basis verified in common-garden
laboratory experiments
HANDOUT—Conover and Present 1990
Categorizing
Life-History
Strategies
r- and K-selection
 Pianka
(1970)
 Name denotes r and K in logistic growth
equation
• r is intrinsic rate of increase
• K is karrying kapacity
Table 10.2 p. 180
Fig. 10.20 p. 181

Grimes (1979)
 Ruderal, competitive, and tolerant plant life
histories
Salisbury (1942)
 The
Reproductive Capacity of Plants
 Anticipated the r-selection/K-selection
dichotomy in plants, measuring the mass
in mg of various plants' seeds:





Open habitats:
120 mg
Semi-closed:
220 mg
Meadows:
490 mg
Wood margins:
440 mg
Shaded habitats: 1400 mg
Fig. 10.21 p. 182

Larger seeds
have higher
survival rates
Bet Hedging
 Some
species spread reproductive effort
over long lifespan
 May have unpredictably variable juvenile
mortality that is often high
 Hence no advantage to investing heavily
in reproduction in any year—trade reduced
reproductive effort off against increased
adult survival

Opposite of “big bang” reproducers
p. 138


Bet hedgers in lower left
Big-bang reproducers in upper right