Organisms at Big Basin
Redwoods were adults when
Rome invaded England in 300A.D.
Mayflies are adults 1 day.
• Each has different life histories:
• timing of, & investment in, reproduction
Offspring Number vs. Size:
Principle of Allocation
•
Energy to one function (e.g. growth) reduces energy
for other functions.
•
∴ trade-offs between number vs. size of offspring.
Offspring Number vs. Size:
Principle of Allocation
•
Energy to one function (e.g. growth) reduces energy
for other functions.
•
∴ trade-offs between number vs. size of offspring.
Offspring Number vs. Size:
Principle of Allocation
•
Energy to one function (e.g. growth) reduces energy
for other functions.
•
∴ trade-offs between number vs. size of offspring.
For 15 darter spp. in Midwest rivers
Seed Dispersal Strategies:
Life History Influences Plant Tactics
•
Some plants make many, small seeds.
•
Others make fewer, larger seeds.
Seed Size & Number:
Advantages of Larger Seeds
•
Their energy reserve
boosts seedling growth.
• This leads to increased
recruitment.
Survivorship Influences
Age at Maturity
•
•
Energy budgets differ before & after maturity.
•
Before - maintenance & growth.
•
After - maintenance & growth & reproduction.
Prediction by Shine & Charnov:
•
Delayed repro allows reaching a larger size.
•
Low adult mortality selects for delayed reproduction.
•
High adult mortality selects for early reproduction.
Survivorship Influences
Age at Maturity
• Reptiles with ⇑ survivorship • Fish w/ ⇑ adult mortality
•
•
delay age at 1st reproduction.
Type of survivorship curve?
•
•
⇓ age at maturity, and
⇑ reproductive rate
Survivorship Influences
Age at Maturity
•
Energy budgets differ before & after maturity.
•
Before - maintenance & growth.
•
After - maintenance & growth & reproduction.
•
•
∴ delayed repro allows reaching a larger size.
Prediction by Shine & Charnov:
•
•
High adult mortality selects for early reproduction.
•
Low adult mortality selects for delayed reproduction.
There’s an energy tradeoff, but also true is that:
•
Delayed reproduction facilitates low adult mortality.
•
Early reproduction induces high adult mortality.
Life History Classification:
r-Selection vs. K-Selection
• r-selection (per capita rate of increase)• K-selection (carrying capacity)
• Few, large offspring
• Many small offspring
• Late maturation
• Early maturation
• Iteroparity
• Semelparity
• Good competitors
• Stable environments
• High popn growth rate
• Type 1 survivorship
• Variable environments
• High parental care
• Type 3 survivorship
• Altricial young
• Low parental care
•
Precocial young
Life History Classification:
r-Selection vs. K-Selection
• r-selection (per capita rate of increase)
•
• K-selection (carrying capacity)
• Few, large offspring
Many small offspring: 300,000,000
•
4
Pianka: r and K are ends of a continuum, most organisms are
along gradient - but what about outliers? - new schemes?
Life History Classification:
1. Ruderals = weedy = r-type!
•
not competitive
•
need disturbed habitats
•
grow & make seeds quickly
2. Stress-Tolerant = K-type?
•
high physical stress
•
grow slow, conserve resources
3. Competitive = K-type?
•
low disturbance & stress
sigmoidal!
Life History Classification:
Opportunistic, Equilibrium, & Periodic
Winemiller & Rose tradeoffs between:
•
age at 1st reproduction α
•
juvenile survivorship (lx)
fecundity (mx)
•
Categorizing animals as
1.
Opportunistic - colonizers
low lx - low mx - early α
•
2.
Equilibrium - K-type
high lx - low mx - late α
•
3.
Periodic - e.g., Molas
What You’ve Learned
• For both plants & animals there’s
•
a tradeoff in offspring size vs. number: Principle of Allocation
•
great variation in allocation of reproductive investment
• Smaller young = greater gene flow
• Larger young = greater recruitment
• Delayed repro allows reaching a larger size.
• Low adult mortality selects for delayed reproduction.
• High adult mortality selects for early reproduction.