bsci160 - population ecology 3

demography

tracking vital statistics of a population over time

• nonbio → population study based on age, race, sex, etc

• includes

  • birth rates

  • death rates

  • immigration rates

  • survival to reproductoin

life table

an age-specific summary of the survival pattern of a population

• made by following fate of group of ind. of same age

• survivorship curve

life table example

tracking ind. over time based on

• sexual maturity age

• fertility over time

• # offspring per female

• survival to next year for each stage

survivorship curve

a graphic way of representing the data in a life table

• 3 types

  • type 1 → drop off

  • type 2 → linear, steady

  • type 3 → ↓ exponential

What kind of survivorship curve would you expect a maple tree to have?

a) type 1

b) type 2

c) type 3

survivorship patterns

life history traits affect timing of repro & survival

• evolutionary outcomes

  • repro age begins

  • repro frequency

  • # offspring / repro cycle

  • more

• limited amt of energy

  • trade-offs → split energy across survival, repro, & growth

tradeoffs

reproduction frequency

• semelparity - single repro (fish)

  • ↑ # offspring

• iteroparity - repeated repro after certain age (dog)

  • ↓ # offspring

offspring size & provisioning

• produce ↑ # small seeds → some will survive (not all)

• produce moderate # of large seeds that provide ↑ energy → most will survive

  • quantity vs quality

survivorship curve table

life history evolution

driven by the environment

• stable / unstable

• predictable / unpredictable

environment stability

balanced organism

low energy investment

• repro early in life

  • repro 1 time

• short lifespan

• few offspring

  • small offspring

• slow growth

• no parental care of offspring

• few defensive traits

high energy investment

• repro late in life

  • repro seasonally

• long lifespan

• many offspring

  • large offspring

• fast growth

• extensive parental care

• many defensive traits

What traits would you expect to see in a balanced organism?

energy allocation

need a balance to allow a continuum of strategies (fast/slow)

exponential vs logistic growth

survival strategies

• r-selected

  • want ↑ repro rates (↑ r)

• K-selected

  • quality > quant. → near carrying capacity (K)

everything connected

bet-hedging

making a variety of offspring types to try to maximize # that survive

• strategy for highly variable environments (unpredictable & unstable)