Populations

1
Populations

• Unit 4
• Biology 1

2
Characteristics of Populations

• Three characteristics are geographic
  distribution, density, and growth rate
• Population density the number of individuals
  per unit area

3
Populations

• Population growth leads to an increase in food,
  energy and other resource consumption
• Carrying capacity is the maximum population a
  given environment can reasonably sustain

4
Population Growth

• Three factors can affect population size
• Number of deaths
• Number of births
• Number of individuals that enter or leave the
  population

5
Population Growth

• Immigration movement of individuals into an area
• Emigration the movement of individuals out of a
  population

6
Exponential Growth

• Occurs when the individuals in a population
  reproduce at a constant rate
• Characterized by doubling
• Starts slowly, but rapidly increases
• Total growth in one doubling is more than the
  total of all preceding growth
• Exponential growth occurs when the rate of growth
  is directly proportional to the number present
• ?N/?t N

7
Exponential Growth

• Doubling time equation is
• Doubling time 70/ of annual growth (r)
• So if the annual growth rate is 2 then 70/235
  years to double the population

8
Limiting Factors

• A limiting factor causes the population growth to
  decrease.
• Two types
• Density-dependent factors
• Density-indepentent factors

9
Density-Dependent Factors

• A limiting factor that depends of a population
  size
• Include competition, predation, parasitism and
  disease

10
Density-Dependent Factors

• Competition when populations become crowded
  organisms compete for food, water, space,
  sunlight and other essentials
• Niche role of an organism

11
Density-Dependent Factors

• Predation
• Predator-prey relationship
• Parasitism and disease
• Similar to predators, but with microscopic
  organisms

12
Density-Independent Factors

• Affects all population regardless of population
  size
• Include natural disasters, seasonal cycles, human
  activities

13
Human Population

• In the beginning of history the world population
  has changed very little because the death rate
  and birth rate were relatively equal
• However, recently the birth rate began to out
  number the death rater?
• Why?

14
Human Population
15
Human Populations

• Changes in population size are recorded and
  monitored by demographers
• Demographers use the numerical equation to
  express changes in the population
• Population growth Birth rate death rate
• This does not take into consideration immigration
  and emigration

16
Human Populations
17
Age-Structure Diagrams
18
Future of Human Population Growth

• It is predicted that the worlds population will
  stabilize at 10.2 billion by 2100 and the
  replacement level of 2 children per couple will
  be reached by 2035
• However, some say the population will not
  stabilize until 11.2 billion
• How did they come up with this data?
• Declining importance of children needed for labor
• Increased cost of raising children
• Improved social status of women
• Rising education level and improved employment