Life Histories (Ch. 12)
Dec 18, 2015
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 • 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
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 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: 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• 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?
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)