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 CorrelationsPregnancy Duration versus Body Size

May & Rubenstein, 1984 Clutton-Brock, 1991

Offspring carried

Offspringindependent

Offspring keptIn the nest

Broad Scale Life-history CorrelationsMaximal Life Span versus Body Size

Stearns, 1992

Not the slopes but the level is interesting

Prothero & Jürgens, 1992

Life Span is Tremendously Variable

274 Species of Invertebrates 170 Mammal Species in Zoos

Stearns, 1992

Comfort, 1979

Stearns, 1992

Eisenberg, 1981

Broad Scale Life-history CorrelationsEgg 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

ConcaveActual fitness contours

Option Sets

Iteroparity Annual Semelparity

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 age-specific survival rates: pjuv (juveniles) and pad (adults)

• Now the fitness of these two reproductive types is equal when:

ada p

juv

pB B

p

• Conclusion: Because pad >> pjuv in many populations, it is often best to be iteroparous

• See Compendium for Details

The Cost of ReproductionTrade-off clear

unclear

Offspring Size versus Offspring #

14.11

14.17

High CRLobelia’s on Mt. Kenia

Problems in the Measurement of Trade-offs

Stearns, 1992

Survival

Reproduction

Fraction to R

A = R + S Var A >> Var B

Var A << Var B

Trade-offs (genetic correlations) may be invisible in the field

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

Geometric mean fitness is often a better measure than arithmetic mean fitness √Y1.Y2.Y3.Y4.....Yn

n

Boyce & Perrins, 1987 Cockburn, 1991

Large SD meanslarge Temporalvariation in Fitness

Clutch Size Optimisation

Other factors also play a decisive role: Laying date

Clutch size is a phenotypically plastic life-history traitDaan et al., 1990 Krebs & Davies, 1991

Model Predictions Match Observations in the Field

14.24

Size and Age at Maturity

Reznick & Endler, 1982 Cockburn, 1991

3 Streams with Different Predation Risk

C = High Adult Pr.R = Moderate Juv. Pr.A = Low Predation

% Female Biomass Reproduction

A transplantation experiment reproduced these patterns in 11 years (30-60 generations)

R: Size & Age at Maturity

C: ReproductiveEffort

R&C: Body Size ↓

Table 14.1

Size and Age at Maturity

Comparative data corrected for body size

14.27

Reproductive ValuePhlox drummondii

Age at maturity Life Span

Age at Maturity= Constant

Cockburn, 1991 Charnov & Berrigan, 1991

But only within taxa

14.16

cf. 14.4

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

Sex ratio and Cost of Reproduction

Only females in their prime age can reproduce each year

Male calfs are usually more ”expensive”Clutton-Brock, 1984, 1991 C

lutt

on

-Bro

ck, 1

98

1, 1

99

1

Sex ratio and Cost of Reproduction

a: daughters are more expensive

A paper on human twins of different sex

Clutton-Brock et al., 1982

Sons

Daughters

b,c,d: sons are more expensive

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

3 papers this afternoonKirkwood, 1985 Stearns., 1992

Excess Repair is not Favoured by Selection

Phenotypic Plasticity

Reaction norms of isofemale lines

Differences in slopes are particularly importantbecause this genetic variation is easy to maintain

Reaction Norm Theory

Size and Age at Maturity Reproductive Effort versus Survival

Stearns, 1989, 1992

Practical Examples

Drosophila mercatorum Human females

Gebhardt & Stearns, 1988; Stearns, 1992 Stearns & Koella, 1986; Stearns, 1992

14.22

Good Nutrition

Bad Nutrition

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