Chapter 5 Populations

Biotic Potential: The size a population would reach if all offspring were to survive and reproduce

• Conditions have to be ideal- enough food and living space

Population Density- Number of individuals in an area

• What Determines density and distribution?

• Geographic Distribution- range- the area the population inhabits

Population Growth

• Affected by -Birth rate (natality)

-Death rate (mortality)-Immigration- entering an

area-Emigration- leaving an area

Populations increase if births exceed deaths and immigration exceeds emigration

Exponential Growth

• Exponential Growth occurs when the individuals in a population increase at a constant rate

• Look at graph on p.121

-under ideal conditions-population grows slowly

at first-rises to an infinitely large

size-J-shaped curve

Logistic Growth

• Logistic growth occurs when a population’s growth slows or stops following a period of exponential growth.

• S-shaped curve-graph levels off

• Carrying capacity- Usually population fluctuates around this point- s-shape

• Look at graph on p. 122

Carrying Capacity

•The number of individuals an area can support without ruining the area.

Limiting Factors

• Something that causes population growth to decrease

• Density dependent• Density independent

Density- Dependent Factors

• Limit a population when the number of individuals reach a certain level

• Competition for food, water, space, sunlight, etc.

• Predation

• Parasitism + disease

Wolf/Moose graph

Density -Independent Factors

• Affect all populations regardless of size

• Weather, natural disasters, seasonal change, human interventions (dams,logging, housing developments)

• Populations usually decrease dramatically after such an event

• Can be permanent + cause extinction

Human Population Growth

• Slow growth historically

• Now, exponential growth- 6-7 billion

• Current World Population

• Some countries have higher growth rates than others

Demographic Transition

• Dramatic change in birth and death rates

• Nutrition, medicine, clean water supplies increase survival rates

• Some countries, population stabilizes, but for a while, births may exceed deaths

Age diagram

• In some cases, populations may even decrease- U.S., Japan, Europe

• Some countries are still growing exponentially

• Parts of Africa, Mexico, India

• Many young people, of an age where they will still be having children

• 9 billion predicted by 2050

• What will stop/slow the growth?