Life Histories(Ch. 12)

Life history trade-offs• Principle of Allocation: Energy used for one

function unavailable for others– Leads to trade-offs (such as number vs. size

offspring)– Exs……

Seed Size vs. Number in Plants• Plant life history variation

• Ex, seed size vs. seed number

Seed Size vs. Number • Scatterhoarded larger (seed reward for dispersal),

wind smaller (lightweight goes farther)

• Dispersal mode influences seed size

Seed Size vs. Number • Does plant growth form influence seed size?

– Growth form: life history feature--body structure

– Graminoids: Grass & grass-like plants.

rushsedge

grass

Seed Size vs. Number • Forbs: Herbaceous (not woody), non-

graminoids.

Seed Size vs. Number • Woody Plants: Woody thickening of tissues.

Seed Size vs. Number • Climbers: Climbing plants & vines.

Seed Size vs. Number • Woody plants + climbers produce larger

seeds

Life history trade-offs• Principle of Allocation: Energy used for one

function unavailable for others– Leads to trade-offs (such as number vs. size

offspring)– Exs……

Life History Trade-offs• Vertebrates….

Life History Tradeoffs• Energy allocated to reproduction: reproductive effort• Energy budgets & sexual maturity.

– Before maturity - maintenance or growth.

– After maturity - maintenance, growth, or reproduction.

• Trade-off:– Delay reproduction: grow faster & reach larger size

– But reproducing early guarantees offspring…..

Life History Tradeoffs• Survival rate correlates positively with age at maturity

Life History: Vertebrate Species• Fish: adult mortality correlates negatively with

age maturity

Life History: Vertebrate Species• Also, mortality

correlates (+) with reproductive effort

• (measured by GSI: ovary weight divided by body weight)

Life History Classification• Principle of Allocation: Energy used for one

function unavailable for others– Leads to trade-offs (such as number vs. size

offspring)

• Classification systems:

• 1) r and K

• 2) CSR (plants)

• 3) Opportunistic, equilibrium, periodic (animals)

• 4) Life history cube (animals)

r and K system• MacArthur and Wilson

– r selection (r: per capita rate of increase)• High population growth rate.

– K selection (K: carrying capacity)• Efficient resource use.

• r and K ends of continuum

E.O. Wilson

r and K system• Intrinsic Rate of Increase (rmax): Highest r selected

species• Competitive Ability: Highest K selected species.• Reproduction:

– r: Numerous individuals rapidly produced.

– K: Fewer larger individuals slowly produced.

Know this Table!

r and K system• semelparity: 1

reproductive event• iteroparity: repeated

reproductive events

• r selection: Unpredictable environments.

• K selection: Predictable environments.

Plant Life Histories (CSR system)

Plant Life Histories• Grime--2 important variables:

– Intensity disturbance: Destroys biomass.– Intensity stress: Limits biomass production

(drought, temperature, salt stress, etc).

Hurricane impact forest

Plant Life Histories• 4 Environmental Extremes:

– Low Disturb. : Low Stress– Low Disturb. : High Stress– High Disturb. : Low Stress– High Disturb. : High Stress

3 strategies

3 Strategies• Ruderals (high disturb. - low stress)

– Grow rapidly, seed fast

• Stress-Tolerant (low disturb. - high stress)– Grow slowly - conserve resources.

• Competitive (low disturb. - low stress)– Compete for resources.

• Last environmental category: high disturb. - high stress?

Plant Life Histories

Life History Classification• Principle of Allocation: Energy used for one

function unavailable for others– Leads to trade-offs (such as number vs. size

offspring)

• Classification systems:

• 1) r and K

• 2) CSR (plants)

• 3) Opportunistic, equilibrium, periodic (animals)

• 4) Life history cube (animals)

Opportunistic, Equilibrium,and Periodic Life Histories

• Winemiller and Rose--classification based on: – 1) age of reproductive maturity ()

– 2) juvenile survivorship (lx)

– 3) fecundity (mx)

– Strategies:

– Opportunistic: low lx - low mx - early – Equilibrium: high lx - low mx - late – Periodic: low lx - high mx - late

Opportunistic, Equilibrium,and Periodic Life Histories

– Opportunistic: low lx - low mx - early – Equilibrium: high lx - low mx - late – Periodic: low lx - high mx - late

Opportunistic, Equilibrium,and Periodic Life Histories

• Same axes: fish most, mammals least variety

Reproductive Effort, Offspring Size, and Benefit-Cost Ratios

• Charnov (life history cube)– Convert life history features to dimensionless

numbers.– Remove influences time & size: reveals

similarities/differences

Reproductive Effort, Offspring Size, and Benefit-Cost Ratios

• 1) Reproductive effort per unit of adult mortality (proportion body mass allocated to reproduction per unit time, divided by adult mortality rate)– scales reproductive effort to mortality cost

Reproductive Effort, Offspring Size, and Benefit-Cost Ratios

• 2) Relative reproductive lifespan (length reproductive life divided by time to maturity)

Reproductive Effort, Offspring Size, and Benefit-Cost Ratios

• 3) Relative offspring size (mass of offspring at independence, divided by adult mass)

Reproductive Effort, Offspring Size, and Benefit-Cost Ratios

• Place organisms in “life history cube”

• Fish, mammals, altricial birds (provide care for young) separate well