Chapter 35:Population Growth

Chapter 35:Population Growth

• Ecologists study the relationship between biotic and nonbiotic factors at 5 levels:

A. Organisms

B. PopulationsC. CommunitiesD.

Ecosystems

E. Biosphere

II. Levels of Organization

A. PopulationA. 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

• Occurs when the individuals in a population reproduce at a constant rate.

J CURVE!

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)

Carrying capacity (K)

Pressure begins due to environmental

resistanceLag phase

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