1. Chapter 53 – Population Ecology

2. Population Ecology
The study of populations in relation to the environment, including environmental influences on population density and distribution, age structure, and variations in population size
Population – a group of individuals of a single species living in the same general area

3. Density Number of individuals per unit area or volume
Affected by immigration, emigration, natality, and mortality
Measure by mark-recapture methods

4. THINK TANK TIME! B A C
Describe the three population dispersion patterns shown above.
What would lead to patterns like this in nature?

5. Dispersion Clumped – aggregated in patches Uniform – evenly spaced
Random – patternless
The pattern of spacing among individuals within the boundaries of the population

6. THINK TANK TIME! B A C
Compare and contrast these 3 survivorship curves.
What reproductive strategies do you think are being used by the organisms represented in each?

7. Demography
The study of the vital statistics of populations and how they change over time (particularly birth and death rates).
Survivorship curve – a plot of the numbers in a cohort (group of same age) still alive at each age
3 basic types of curves: I, II, and III, but there are variations to each (ex. crabs)
I = flat at the start, reflecting low death rates during early and middle life, then drops steeply as death rates increase among older age groups.
II = are intermediate, with a constant death rate over the organisms life span
III = curve drops sharply at the start, reflecting very high death rates for the young, but then flattens out as death rates decline for those few individuals that have survived to a certain age.

8. Population Life History “Strategies”
r-selected (opportunistic)
Density independent
Birth rate/death rate does NOT change with population density
Maximizes r (rate of increase)
Short maturation and life span
Many small offspring
Usually only 1 or 2 reproductions early in life
No parental care
High death rate
k-selected (equilibrial)
Density dependent
Death rate rises with population density
Maximizes population size
Long maturation and life span
Few large offspring
Usually several reproductions later in life
Extensive parental care
Low death rate

9. Population Growth Models
Change in population size: dN/dt = rN
N = population size
t = time
r = per capita birth rate (b) – per capita death rate (m)
Exponential model – idealized, unlimited environment:
dN/dt = rmaxN
Logistic growth model – includes carrying capacity (K), the maximum population size that a particular environment can support:
dN/dt = rmaxN((K-N)/K)

10. THINK TANK TIME!
Analyze the graph below and describe the relationship between the snowshoe hare population and the lynx.
How can this be explained?

11. Limiting Factors
Density independent factors – weather, climate, disturbances
Density dependent factors – competition, predation, stress, habitat, territoriality, crowding, health, disease, and waste accumulation