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Chapter 4
Population Biology
Linear Growth
Rainfall
Rainfall in millimeters
Growth occurs in a
straight line when
graphed. Steady
equal increase.
12
10
8
Day
6
Rainfall
4
2
0
1 2 3 4 5 6 7 8 9 10
Day
Exponential Growth
As a population gets
larger, it also grows
faster. Natures
population growth.
J-CURVE
Questions To Think About
Can a population of organisms grow indefinitely?

NOOOOOOOOOOOOOOO
Why?
What will limit the population from growing?
Natural Disaster
Disease
Food Supply
War
Stop Reproducing
S-Shaped
If a population starts
to level off it is known
to have a S- Shape
Similar to Carrying
Capacity
Effects of Competition
Competition density-dependent factor

Depends on population size
Effects of Crowding And Stress
Aggression
Decrease parental care
Decreased resistance to disease
Demography
Study of human population growth
characteristics
Demographer studies population
characteristics as growth rate, age
structure, and geographic distribution
Effects of Birth and Death Rates
Growth Rate – is the difference between
the birthrate and the death rate
What is the trend of the U.S.?
Age Structure – can help predict if a
population is growing rapidly, growing
slowly or not growing at all.
Immigration – movement into a population
Emigration – movement from a population
Carrying Capacity
The number of organisms
of one species that an
environment can support.
When populations are
under the carrying
capacity births > deaths
until the carrying capacity
is reached
Populations exceeds
carrying capacity deaths
> births
Environmental Limits to Population
Growth
Limiting Factors


Density Dependent Factors – disease,
competition, parasites, and food have an
increasing effect as the population increases
Density Independent Factors – affect all
populations regardless of their density
Ex. – hurricanes, abiotic factors, storms, floods
Organisms Interactions Limit
Population Size
Predation Affects Population Size
1. when predator consumes prey, it can
affect the population size of the prey
population
2. Predator Prey Relationships Very
Healthy For Populations