Introduction to Populations

1. (Modern Biology: Chapter 19)
Population Ecology

2. Properties of Populations
 Population: a group of organisms of one species
in the same area at the same time (defined space
and time)
 1) Population Size = number of individuals
 Can be difficult to measure directly

3. Properties of Populations
2) Population Density = how crowded a
population is
 Expressed as # of individuals per unit area or volume
 Ex: United States Population Density (Homo
sapiens)
30 people/km2

4. Properties of Populations (con’t)
 3) Dispersion = the spatial distribution of
individuals
 3 types:
A) Uniform (aka. Even)
B) Clumped
C) Random

5. Population Growth Rate
 All populations are dynamic.
They change in size and composition over
time.
 Scientists who study population dynamics =
DEMOGRAPHERS
 GROWTH RATE of a population is the
amount by which a population’s size
changes in a given time.
Can be positive (Increasing population
over time)

8. Exponential Growth
 Describes a population that grows rapidly after
only a few generations
 “J-curve”
 Larger population = faster growth
 In reality, resources will run out
 Limiting Factor: a factor that restrains population
growth
 ALL populations are ultimately limited by their

9. Population Regulation
 Two type of limiting factors have been identified:
1) Density-independent: population density does not
matter
 i.e. weather, floods, fires, climate change
 The population is reduced by the same proportion regardless of
size/density
2) Density-dependent: depend on population density
 i.e. availability of resources, space

10. Logistic Growth
 Describes a realistic population
 Accounts for limiting factors
 “S-Curve”
 Carrying Capacity: the maximum # of individuals
the environment can support over time