Population

Ecology

I. Population Dynamics

• Population:

•All the individuals of a species that live together in an area at the same time.

• Demography/Demographics:

•The statistical study of populations

•allows predictions to be made about how a population will change over time.

II. Three Key Features of

Populations

1a. Size: number of individuals

in an area (aka: how many?)

Three Key Features of

Populations

Population growth rate can drastically

change population size:

•Birth Rate (aka natality) - Death Rate

(mortality)

•How many individuals are born vs. how

many die in a given year?

•1b. Birth rate (b) − death rate (d) =

growth rate (r)

2. Density: measurement of population

per unit area or unit volume

Pop. Density = # of individuals ÷ unit of

area

Three Key Features of

Populations

a. Immigration: movement of individuals into a population

b. Emigration: movement of individuals out of a population

c. Density-dependent factors: Biotic factors in the environment that have an increasing effect as population size increases (disease, competition, parasites)

d. Density-independent factors: Abiotic factors in the environment that affect populations regardless of their density (temperature, weather)

3. How Do You Affect Density?

Immigration

Emigration

Natality MortalityPopulation+

+

-

-

Factors That Affect Future Population

Growth

4. Dispersion: how spread out individuals

in a population are

•Clumped

•Uniform

•Random

Three Key Features of

Populations

• 5a. count all the individuals in a

population, called a direct count

(actual #)

• 5b. Estimate by:

• Random sampling – stationary species

• Mark-recapture method – mobile species

• Remember % error??? Formula???

5. How Are Populations

Measured?

6a. R Strategists

a. Short life span

b. Small body size

c. Reproduce

quickly

d. Many young

e. Little parental

care

f. Exponential

growth (J-curve)

Ex: cockroaches,

weeds, bacteria

6. Reproductive Strategies

6. Reproductive Strategies6b. K Strategists

a. Long life span

b. Large body size

c. Reproduce slowly

d. Have few young

e. Provides

parental care

f. Logistic growth

(S-curve)

Ex: humans,

elephants

6. Reproductive Strategies

Summary

7. Carrying Capacity

• Carrying Capacity (k):

• The maximum population size that can be

supported by the available resources in

each environment

• KEY POINT HERE… There can only be as

many organisms as the environment’s

resources can support

• Declining birth rate or increasing death

rate (negative “r”) are caused by several

factors including:

a. Limited resources (food, H2O, space)

b. The buildup of toxic wastes

c. Increased disease

d. Predation

e. Competition

8. Factors that Limit

Population Growth Rate

“Boom” and “Bust” Cycles

“Boom” characterized

by rapid growth witch

is followed by “busts”

during which the

population falls back to

a minimal level.

Age Distribution

• Distribution of males and females in

each age group of a population

• Used to predict future population

growth

Human Population

Growth

• J curve growth

• Grows at a rate of about 80 million yearly

• r =1.3%

• Why doesn’t environmental resistance take effect?

• Altering their environment

• Technological advances

•The cultural revolution

•The agricultural revolution

•The industrial-medical revolution

• Doubled three times in the last three

centuries

• About 6.1 billion and may reach 9.3

billion by the year 2050

• Improved health and technology have

lowered death rates

The Human Population

History of the Human Population