Biology Bellwork – 10/17/12• Describe some observations you can make

about populations of insects over the course of a year?

• The populations of flies or mosquitoes go up in the spring and summer and decline in the fall. Do they die out completely in winter?

• A few individuals in each population find places to go over-winter, and some migrate.

Biology Bellwork – 10/24/12• Explain how the improvement in shelter can increase

the survival rate of a human population.• Adequate shelter provides defense against extremes of

the environment such as temperature, precipitation, and wind. In addition, shelter provides defense against biotic factors in the environment such as venomous snakes, mosquitoes, other insects that harbor parasite, and large predators such as wolves and bears. All of these have the potential to shorten the life span of individuals, thereby affecting the human population as a whole.

Alternative Assignments• Write a paragraph comparing density-

dependent and density-independent factors that can limit human populations.

• Imagine that you are a housefly. Write a short comic strip, with illustrations, explaining what it is like to be a r-strategist from a fly’s view-point.

Bellwork 10/25/12• Define the followings vocabulary terms:

• Carrying Capacity•The maximum number of individuals in a

species that an environment can support for the long term.

•Limiting Factor•Biotic or abiotic factor that restricts the

number, distribution, or reproduction of a population within a community.

Population Ecology

Population Dynamics

• Population:• All the individuals of a species that live

together in an area at the same time

• Demography:• The statistical study of populations,

allows predictions to be made about how a population will change

Population Dynamics

• Three Key Features of Populations• Size• Density• Dispersion

Three Key Features of Populations

Size: number of individuals in an area

Three Key Features of Populations

• Growth Rate: • Birth Rate (natality) - Death Rate (mortality)• How many individuals are born vs. how many

die• Birth rate (b) − death rate (d) = rate of natural

increase (r)

Density: measurement of population per unit area or unit volume

Pop. Density = # of individuals ÷ unit of space

Three Key Features of Populations

1. Immigration: movement of individuals into a population

2. Emigration: movement of individuals out of a population

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

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

How Do You Affect Density?

Immigration

Emigration

Natality MortalityPopulation+

+

-

-

Factors That Affect Future Population Growth

• Dispersion: describes the spacing of organisms relative to each other• Clumped• Uniform• Random

Three Key Features of Populations

Population Dispersion

• Population density = number of individuals in a given area or volume

• Count all the individuals in a population• Estimate by sampling• Mark-Recapture Method

How Are Populations Measured?

• Idealized models describe two kinds of population growth:

1. Exponential Growth

2. Logistic Growth

How Do Populations Grow?

Bellwork – 10/26/12• An employer offers two equal jobs of one hour

each for fourteen days. The first pays $10/hour. The second pays only 1 cent the first day, but the rate doubles each day.

• Which job would you rather have?Job #1 $10 x 14 days = $140Job #2 $0.01 + $0.02 + $0.04 + $0.08 + $0.16 +

$0.32 + $0.64 + $1.28 + $2.56 + $5.12 + $10.24 + $20.48 + $40.96 + $81.92 = $163.83

Figure 35.3A

Exponential Growth Curve

Logistic Growth Curve

• Declining birth rate or increasing death rate are caused by several factors including:• Limited food supply• The buildup of toxic wastes• Increased disease• Predation

Factors Limiting Growth Rate

“Booms” and “Busts”

• R Strategists Short life span Small body size Reproduce quickly Have many young Little parental care Ex: cockroaches,

weeds, bacteria

Reproductive Strategies

Reproductive Strategies

• K Strategists Long life span Large body size Reproduce slowly Have few young Provides parental

care Ex: humans,

elephants

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