Transcript Population Growth

Chapter 35:
Population Growth
II. Levels of Organization
• Ecologists study the relationship
between biotic and nonbiotic factors
at 5 levels:
A.
Organisms
B. Populations
C. Communities
D. Ecosystems
E. Biosphere
A. Population
• Definition: a group of individuals of the
same species living in a particular area at
the same time
B. Population density = # of individuals
-----------------unit area of space
How do you calculate population
density?
Example:
If there are 10 red tail hawks in a 5 mile2
piece of land, what is the density of hawks
per mile2?
A: 10 ÷ 5 = 2 hawks/mi2
A. Exponential Growth

Definition: under ideal conditions with unlimited
resources, a population will grow exponentially
J CURVE!
• Occurs when the individuals in a population
reproduce at a constant rate.
C. Logistic Growth

Exponential growth does not continue for very long

Growth slows or stops as resources become less available
• Logistic growth
occurs when a
population's
growth slows or
stops following
a period of
exponential
growth
E. Carrying Capacity

Carrying capacity is the largest # of individuals of
a population that an environment can support
F. As a population approaches Carrying
Capacity, average growth rate reaches
ZERO (levels off)
Population
Numbers
Carrying
capacity (K)
Lag phase
Pressure begins due to
environmental
resistance
Time
Limiting Factors

Factor that causes population growth to
decrease
 Density-Dependent
limiting factor that depends on population size

Density-Independent
affects all populations in similar ways, regardless
of the population size
Density-Dependent Factors

A limiting factor that depends on population
size
Food, clean water
 competition
 predation
 parasitism
 disease

Density-Independent Factors

Affect all populations in similar ways, regardless of the
population size




unusual weather
natural disasters
seasonal cycles
certain human activities—
such as damming rivers
and clear-cutting forests
Human Population Growth
A. Human population began growing more rapidly about 500
years ago because life was made easier and safer by
advances in agriculture and industry
B. Life improved for humans (and death rates reduced)
due to:
 Improved sanitation
 Medicine and healthcare
Birthrates remained high
With these advances, human population
experienced exponential growth
C. Factors that affected pop growth:
- Agriculture
- Bubonic Plague
- Industrial Revolution
WHAT TREND DO YOU SEE
ON THIS SLIDE COMPARED
TO NEXT SLIDE?
E. Current population and beyond
* There are currently 7.1 BILLION people in the world
* By the time you are in your 50’s, it is estimated there
could be up to 9.6 BILLION!
Source: UN.org Report World Population Projections, June 2013
link


Negative population growth has been seen
in:
Germany, Japan, and Russia among other
countries.
Growth in U.S. & much of Europe has
slowed dramatically
In the Future
F. Ecologists suggest that if growth does not slow down,
there could be serious damage to the environment and
global economy.
G. How can population growth be helped?
 Science
 Technology
 Use of contraceptives
 Smaller family sizes
 Starting family at older age
 Education