1. Chapter 52 Notes
Population Ecology

2. Characteristics of Populations
Population: a group of individuals of a single species that simultaneously occupy the same general area
Two important characteristics of any population are density and the spacing of individuals
Density: the number of individuals per unit area of volume

3. Characteristics of Populations
Dispersion: the pattern of spacing among individuals within the boundaries of the population
The mark-recapture method can be used to measure population density
N= number in 1st catch X total in 2nd catch
number of recaptures in 2nd catch

4. Characteristics of Populations
3 Patterns of Dispersion
Clumped: the individuals are aggregated into patches
ex. mushrooms, animals that move in herds
Uniform: evenly spaced; may result from direct interactions between individuals
ex. territorial behavior, competition

5. Characteristics of Populations

6. Characteristics of Populations
Random: occurs in the absence of strong attractions or repulsions
Demography is the study of factors that affect the growth and decline of populations
- additions occur because of birth and immigrations

7. Characteristics of Populations
- eliminations occur because of deaths and emigration
Life tables are used as a summary of the survival patterns of a population
- survivorship curves plot the data for a life table
- type 1 curve: low death rate during early and middle ages; drops steeply with age

8. Characteristics of Populations
- type 3 curve: high death rate among young, then flattens out as death rate declines for adults
ex. marine invertebrates
- type 2 curve: mortality is constant over lifespan
ex. annual plants, grey squirrel

9. Characteristics of Populations

10. Life History
Life histories are diverse, but they exhibit patterns in their variability
- big-bang reproduction: some plants and animals invest most of their energy into growth and development, and then expend their energy in 1 large reproductive effort; also called semelparity

11. Life History

12. Life History
- repeated reproduction: organisms produce fewer offspring at a time, but do so over many seasons; also called iteroparity
- limited resources mandate trade-offs between investments in reproduction and survival

13. Population Growth
The exponential model of population growth describes an idealized population in an unlimited environment
Change in pop size = births – deaths
DN/Dt = B-D
Scientists use r to represent the difference in per capita birth and death
r = b-d

14. Population Growth
Zero population growth (ZPG) occurs when the birth rate equals the death rate ( r = 0)
Intrinsic rate ( rmax) is the fastest growth rate possible reproducing under ideal conditions

15. Population Growth
Exponential growth is a population increase under ideal conditions
dN/dt = rmaxN
- the population increases rapidly
- J shaped growth curve

16. Population Growth
The logistic model of population growth incorporates the concept of carrying capacity
Carrying capacity: the maximum population size that an environment can support
- symbolized as K
- when N = K, the growth rate = 0

17. Population Growth
Carrying capacity
Number of Yeast Cells
Time (hours)

18. Population-limiting factors
Factors that limit growth are both density-dependent and density-independent
Density dependent: death rate will rise as the population density rises
- predation-prey
- competition for food

19. Population-limiting factors

20. Population-limiting factors
Density independent: birth and death rates do not change with density
- mainly caused by weather and climate
- not caused by negative feedback