Population Dynamics

1
Population Dynamics
100 m2 sampled to determine the density of animal
species X N ? M 140 n 130 m 50 Density
estimate is 364 individuals of X/100 m2 With
Yates correction 360 individuals of X/100 m2
2
Estimating population density mobile animals

• Mark-recapture technique (Lincoln-Peterson
  Index)
• N M n m
• N/M n/m
• N population estimate
• M number captured time 1 and released back into
  population
• n total number captured at time 2
• m number marked individuals captured at time 2
• N Mn/m (overestimates population size)
• Bailey correction N M(n 1)/m 1)

3
Estimating patterns of survival

• Have to know when individuals die (their ages)
• Track a cohort of newly produced individuals
  until all have died.
• Collect parts of dead individuals that indicate
  age at death.

4
Population age structure

• Age of individuals generally difficult to
  ascertain
• Many organisms do not mark passage of time with
  phenotypic markers
• However, those with interrupted growth may
• e.g., trees and vertebrates in habitats with
  seasonal differences
• trees growth rings
• sheep horn annuli
• Tooth replacement and wear may provide estimates

5
608 is adjusted to 1,000 individuals
Based on 608 skulls 121 deaths age 0-1 121/608
X/1000 X 121,000/608 199
Dall sheep
Survivorship curve
Survivorship pattern death occurs
principally in old individuals
Source Murie 1944
6
.
Survival among annual plant and rotifer
populations
Survivorship pattern death occurs principally
in older age classes
Source Leverich and Levin 1979, and Deevey 1947
7
.
Constant rates of survival
Survivorship pattern death is distributed
evenly across age classes
   Source Deevey 1947, Baker, Mewalt, and
Stewart 1981, Frazer, Gibbons, and Greene 1991
8
Typical perennial plant populations
Survivorship pattern mortality greatest
in younger age classes
    Source Hegazy 1990
9
Three types of survivorship curves
   
10
.
Age distribution as an index to a populations
future
Age distribution of white oak population Stability

    Source Miller 1923
11
Age distribution of a Rio Grande Cottonwood
population A population in decline
     Source Howe and Knopf 1991
12
Age distribution of large cactus finches
Geospiza conirostris Isla Genovesa
    Source Grant and Grant 1989