Organism Life Histories BIOL400 9 November 2015

Energy Allocation  An organism assimilates a finite amount of energy, which it can devote to: Growth Growth Reproduction Reproduction Tissue maintenance Tissue maintenance Storage for later (see above) 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 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 Annual Lifetime 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

 House wren??  Red deer  Kenyan Lobelia  Beech trees Fig. 2.9 p. 25 Fig p. 137 Fig 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 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

 Invariant … …ratios (“dimensionless numbers”) …ratios (“dimensionless numbers”) …X-Y relationships with set slopes …X-Y relationships with set slopes  Demonstrate the nature of life-history trade-offs

HANDOUTS—Charnov 1993

Genotype and Phenotype  Is variation in life history… …genetic (induced by DNA)? …phenotypic (induced by environment)? …phenotypic (induced by environment)?

Fig p. 91   Common-garden experiments demonstrate genotypic effect—adaptation to local conditions? All grown in identical greenhouse conditions Yarrow

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 increaser is intrinsic rate of increase K is karrying kapacityK is karrying kapacity

Table 10.2 p. 180

Fig 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 Open habitats: 120 mg Semi-closed: 220 mg Semi-closed: 220 mg Meadows: 490 mg Meadows: 490 mg Wood margins: 440 mg Wood margins: 440 mg Shaded habitats:1400 mg Shaded habitats:1400 mg

Fig 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 Opposite of “big bang” reproducers

p. 138   Bet hedgers in lower left   Big-bang reproducers in upper right