Ecology

Chapter 4: notes

Population Ecology: Growth and density:

For a good list of web sites on population ecology see: Population Ecology Reference List

 

A. Birth and Death:

1.Life tables summarizes statistics death and survival of a population by age:

a). Cohort Population Ecology Reference List

  • Group born at one time

b). Life expectation

  • Average additional time left to individuals alive a particular age
  • Mean natural longevity
  • Physiological longevity - old age

c). Life tables

  • Age specific, age, death
  • Time specific, S, death rates
  • Composite

d). Survivorship curves; survivorship vs age

  • Convex, concave, diagonal

B. Population growth

1. Exponential Growth

  • Exponential population growth dN/dt = rN
  • Nt = Noert
  • Doubling rate 70/% annual growth

2. Biotic potential

a). Intrinsic rate of natural increase

  • Nt = Noert
  • Influence biotic potential
-Fecundity
-S up to reproduction age
-Age at 1st reproduction
-Length of reproduction age

3. Logistic population growth

  • Logistic curve as a model
  • Nt = K/1+ea-rt
  • K = carrying capacity
  • Unrealistic

a). Assumes straight line relationship

  • Density vs effects of crowding
  • Allee effect (need min pop density)

b). Assumes no time lags

  • Need time for pred to adjust to prey change

c). Assumes all individuals respond the same

d). Time lag

  • dN/dt = rNt[(K-Nt)/K] - Pop growth rate influenced by size
  • dN/dt = rNt-c[(K-Nt-w)/K] - pop growth rate influenced by size at earlier time

C. Population density and population regulation

1. Density dependent factors

  • Intercompensation - calamity, death, best habitats available for survivors, production increases

2. Habitat distribution

  • Most suitable habitats are taken first as they get crowed individuals pushed to fringe or to less suitable habitats but are uncrowded
  • Ideal free distribution

3. Carrying capacity

4. Population regulation

a). Extrinsic population interaction with community

  • Predation, parasitism, disease

b). Intrinsic pops own response to density

  • Intraspecific comp, physiol changes affecting reproduction

c). Scramble (exploitation)

d). Contest (interference):

  • Dominance hierarchies
  • Territoriality
  • Inhibitory chemicals (plants)

5. Nonequilibrium populations:

  • Insects tend toward non-equilibrium, whereas birds and mammals tend toward equilibrium populations