1. Population Ecology
Chapter 4

2. Population Density Population density: # of organisms per unit area
Example: 5 deer per square mile of forest
If 10 people are in a 100 square foot room, what is their population density?

3. Spatial Distribution Dispersion: pattern of spacing of a population
Uniform – spread out evenly throughout an area
Clumped – found in clumped groups
Random – spaced out randomly and unpredictable
What does dispersion pattern tell you about an organism?

4. Population Range Where on earth do you find a specific population?
Some organisms are found throughout the world = large population range
Other organisms only found in a few places = limited population range
Why might an organism such
as the Kiwi bird have a limited
population range?

5. Population Limiting Factors
Remember limiting factors keep a population from continuing to grow
These factors may be biotic (ex. predators) or abiotic (ex. temperature)
Decreasing a limiting factor often changes the number of individuals that can survive in an area
Two types of limiting factors on populations
Density-independent limiting factors
Density-dependent limiting factors

6. Density-independent factors
Does not depend on the size of the population
Affects all populations equally no matter how big or small the population is
Usually are abiotic
Often includes natural phenomena such as floods, fires, etc.
Can sometimes be
beneficial to some members
of the community

7. Density-dependent factors
Effect depends on the size of the population
Often biotic
such as predation, disease, parasites, & competition
disease: transmitted easier
when population is larger
competition: occurs more
often when pop. is larger
parasites: more common

8. Population Growth Rate
How fast a population grows
Four factors affect growth rate
1. Natality = birthrate
2. Mortality =
death rate
3. Emigration =
moving out of
a population
4. Immigration =
moving into a
population

9. Exponential Growth Growth begins slowly but then takes off quickly
Creates a J-shaped curve on a graph
Exponential phase = growth is quick
Lag phase = growth is slow

10. Logistic Growth
Population grows exponentially until some limiting factors slows its growth
Forms an S-shaped
curve on a graph
Carrying capacity = max
number of individuals
an ecosystem can
support

11. Reproductive patterns
Reproductive patterns of different species vary
may have different # of births per cycle
May begin reproducing at different ages
May have different life spans
R-strategist and k-strategists

12. r-strategists Also called the rate strategy
Used by organisms that live in environments where biotic and abiotic factors often fluctuate
characteristics
1. Usually are small
organisms
2. Usually have short
life spans
3. Usually produce
many offspring at once

13. k-strategists k refers to carrying capacity
Used by species living in areas with predictable and fluctuations in the environment
Characteristics
1. usually larger
organisms
2. usually have
long life span
3. only produce
a few offspring
at a time

14. Human Population Growth
Demography: study of the human population
Includes size, density, distribution, movement, birthrate and deathrate

15. Human Population cont.
Has grown rapidly as humans have learned to alter their environment.
Better agriculture, domestication of animals, technological advances, and discoveries in medicine

16. Zero Population Growth (ZPG) & Age Structure
ZPG occurs when births + immigration = deaths + emigration
Age structure: # of people in each age group in a population
Pre-reproductive, reproductive, & post-reproductive