Transcript Slide 1
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 • • • • 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? • • • • 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