1. Population Ecology
Chapter 52

2. Population characteristics
Density~ # of individuals per unit of area
•counts
•sample size estimate
•indirect indicators
•mark-recapture
Figure 52.17

3. Density is the result of a dynamic interplay
Between processes that add individuals to a population and those that remove individuals from it
Births and immigration add individuals to a population.
Births
Immigration
PopuIation size
Emigration
Deaths
Deaths and emigration remove individuals from a population.
Figure 52.2

4. Population characteristics
Dispersion~ pattern of spacing
•random~ unpredictable, patternless spacing (a)
•clumped~ patchy aggregation (b)
•uniform~ even spacing (c)

5. Demography: factors that affect growth & decline of populations
Birthrate (natality)~ # of offspring produced
Death rate (mortality)
Age structure~ relative number of individuals of each age

6. Demography: factors that affect growth & decline of populations
Survivorship curve~ plot of numbers still alive at each age

7. The survivorship curve for Belding’s ground squirrels
Shows that the death rate is relatively constant
Figure 52.4
1000
100 10 1
Number of survivors (log scale) 2 4 6 8
Age (years)
Males
Females

8. Population Growth Models
Zero population growth
Occurs when the birth rate equals the death rate
The population growth equation can be expressed as dN dt = rN

9. Population Growth Models
Exponential model (red)
• idealized population in an unlimited environment (J- curve)
r-selected species (r=per capita growth rate)

10. ∆ N = rmaxN ∆ t The equation of exponential population growth is
Figure 52.9 5 10 15
500
1,000
1,500
2,000
Number of generations
Population size (N) dN dt =
1.0N
0.5N
∆ N
∆ t =
rmaxN

11. Population Growth Models
Logistic model (blue)
•carrying capacity (K): maximum population size that a particular environment can support (S- curve)
K-selected species

12. ∆N ∆t = K rmax N The logistic growth equation
Includes K, the carrying capacity
Figure 52.13a
800
600
400
200
Time (days) 5 10 15
(a) A Paramecium population in the lab. The growth of Paramecium aurelia in small cultures (black dots) closely approximates logistic growth (red curve) if the experimenter maintains a constant environment.
1,000
Number of Paramecium/ml ∆N ∆t =
(K - N) K
rmax N

13. Population life history “strategies”
K-selection, or density-dependent selection
Selects for life history traits that are sensitive to population density
r-selection, or density-independent selection
Selects for life history traits that maximize reproduction

14. r-selected (opportunistic) K-selected (equilibrial)
Short maturation & lifespan
Many (small) offspring; usually 1 (early) reproduction; no parental care
High death rate
K-selected (equilibrial)
Long maturation & lifespan
Few (large) offspring; usually several (late) reproductions; extensive parental care
Low death rate

15. Population limiting factors
Density-dependent factors
•competition •predation •stress/crowding •waste accumulation
Density-independent factors
•weather/climate
•periodic disturbances