Transcript Three Key Features of Populations Size

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 densitydependent 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)
Three Key Features of Populations
Density: measurement of population per unit
area or unit volume
Pop. Density = # of individuals ÷ unit of space
How Do You Affect Density?
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)
Factors That Affect Future Population Growth
Immigration
Natality
+
+
Population
Emigration
-
Mortality
Three Key Features of Populations
• Dispersion: describes the spacing of
organisms relative to each other
• Clumped
• Uniform
• Random
Population Dispersion
How Are Populations Measured?
• 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 Do Populations Grow?
•
Idealized models describe two kinds of
population growth:
1. Exponential Growth
2. Logistic Growth
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 = $140
Job #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
Exponential Growth Curve
Figure 35.3A
Logistic Growth Curve
Factors Limiting Growth Rate
• Declining birth rate or increasing death rate
are caused by several factors including:
• Limited food supply
• The buildup of toxic wastes
• Increased disease
• Predation
“Booms” and “Busts”
Reproductive Strategies
• R Strategists
 Short life span
 Small body size
 Reproduce quickly
 Have many young
 Little parental care
 Ex: cockroaches,
weeds, bacteria
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
The Human Population
• 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
History of the Human Population