Download Chapter 4- Population Biology

Chapter 4- Population
Biology
Why do humans gather in
cities?
To socialize and obtain
resources easily
What are the drawbacks to
people living in cities?
Space
Population growth
• Population- number of organisms of the same species
living in the same area
• Dispersal- movement of a population from densely
populated locations to new ones
• Population growth- change in the size of a population
over time
• Populations will grow at the same rate if they have
enough resources (ex. Food)
• Population growth is illustrated by a
J-shaped curve
(shows that populations will
grow at the same rate)
J-shaped curve
Also called exponential growth (same rate)
Ex. Flies 2 >> 6 >> 18 >> 54 >> 162 >>486 >> 1458
Log phase
Lag phase
Populations grow slowly at the beginning because
reproduction is slow (lag phase)
Reproduction increases as the number rises making the
population number spike. (exponential phase or log
phase)
S-shaped curve
• Populations will grow rapidly until they start to run out of
resources. Then they will level off called the carrying
capacity (illustrated by an S-curve). Also called the
stable equilibrium phase
Stable equilibrium
or carrying capacity
Log phase
lag phase
• Carrying capacity- the number of organisms the
resources in an area will support
Factors affecting population
growth:
Birth > deaths = population growth
(illustrated in J-curve)
Deaths > births = population decline
(illustrated in S-curve)
There are 2 main factors that restrict
population size:
Food and space
Limiting factors- factors that limits the
size of a population
Why do populations not grow at the same rate?
•
1.
They have different reproductive
patterns
2 types of reproductive
patterns:
Rapid reproduction (ex. Fly)
If an organism lives in a harsh
environment, it must reproduce rapidly
and have large number to increase
chances of survival. Even then, many
die
2.
Slow reproduction (ex.
Elephant)
If the environment is stable and less
harsh, then there is not a need for
rapid reproduction or a lot of
offspring. Parents often take care of
these offspring increasing survival.
Few die. (ex. Human)
Factors that influence population
sizes:
Density dependent
factors- these factors are
dependent on the size
(density) of the population
examples: food, space,
disease
Density independent
factors- these factors are
not dependent on the size
of a population
examples: droughts,
floods, temperature
Population density
• Number of
individuals per
unity area of
space
(ex. There is a
greater
population
density in New
York than in
Muscle Shoals)
Population growth terms
• Natality- number of individuals added to
the population through reproduction over
time
• Birthrate- number of individuals born per
1000 individuals per year
• Mortality- number of deaths in a
population over time
• Death rate- number of deaths per 1000
individuals per year
Computing population growth
• There are 4 components to population growth
Population growth = (births + immigration) –
(deaths + emigration)
Immigration- number of
organisms entering an area
Emigration- number of
organisms exiting an area
Owl pellet lab:
Objectives:
• To abstract bones of prey from a barn owl pellet
• Explain how owl pellets are made and how they are used
to study predator/prey interactions
• Explain the role of predators in the food web and how
their interactions affect the ecosystem
Owl pellet lesson:
• Watch the video on the barn owl and
answer the questions on the worksheet
(15 min.)
• Dissect pellet following the procedures
and fill in the information on the chart (45
min.)
• Clean up and wash hands (10 min)
• Answer the analysis questions (rest of
class and homework)
Review/discussion:
• What role does the owl play in its ecosystem?
• What would happen if the rodents were removed?
• Knowing the pollutants like DDT are magnified through
the food chains, why are higher consumers most
threatened.
• If organisms live in the same area, they must interact
and depend on each other. If an influx of predators
occurred in an area, explain some effects it would have
in the ecosystem. (3 examples)
• Knowing that humans are also predators and that
organisms are interdependent, suppose that our
population had a massive increase and we completely
wiped out the cow population. What are some things that
would result from the removal of this prey? Write a letter
of at least 100 words to your grandchild (future)
describing life 50 years from now without cattle.