life histories

life history

lifetime schedule of reproduction and survival

fitness (life history context)

lifetime production of successful offspring

cost of reproduction

more reproduction now = less survival/reproduction later

Semelparity

reproduce once, then die

Iteroparity

reproduce multiple times

big bang strategy

reproduce early and heavily, then die

when early reproduction is favored

stable environment, low juvenile mortality

when delayed reproduction is favored

high juvenile mortality, variable environment

Advantage and risk of delaying reproduction

pros: grow larger → produce more offspring later

cons: may die before reproducing

Spreading risk across years→ reduces chance of total reproductive failure

dormancy

delayed reproduction via seeds/spores

bet hedging

spreading reproduction across time to reduce risk

Predator satiation

produce many offspring at once to overwhelm predators

Example of predator satiation→ bamboo flowering

Quasi-semelparity

mostly reproduce once but also have some additional reproduction

Senescence

deterioration with age

Why senescence occurs→ weak selection against late-life harmful genes

Why some organisms don’t senesce→ continued reproduction keeps selection strong

Grandmother hypothesis

older females increase fitness by helping offspring’s offspring

Inclusive fitness (life history context)

helping relatives increases gene success

r-selection

selection for rapid reproduction at low density

r-selection environment→ unstable, frequent disturbances

k selection

selection for rapid reproduction at low density

K-selection environment→ stable, crowded populations

r-selected traits

• many small offspring

• early reproduction

• little parental care

• high rmax

k selected traits

• few large offspring

• delayed reproduction

• high parental care

• long lifespan

Juvenile mortality

death rate of young individuals

Density-dependent mortality

death rate depends on population size

Density-independent mortality

death rate independent of population size

Intrinsic growth rate (r)

r = ln(Nt+1 / Nt)