understanding changes in population

1. Is the Population Increasing, or
Decreasing?
 Populations vary dramatically over time
(boom/bust cycles)
 Births (B) and Deaths (D) affect populations
 Immigration (I), when populations move in (I)
and Emigration (E), when populations move
out also affect population
 Change in population = (B-D) + (I-E)

2. What Controls Population Size and
Growth Rate?
• Density-dependent factors:
• competition
•food
•space
•contagious disease
•waste production
•Density-independent factors:
•disturbance, environmental conditions
•hurricane
•flood
•colder than normal winter

3. Example
 The small town of Fruitopia has 526 inhabitants.
Last year there were 25 births, 17 deaths, 12
people moved into the area, and 9 people moved
out of town.
 Calculate the population change. Did the population
increase or decrease?
 Calculate the total population at the end of the year.
 At this rate, what would the population be in 4 years?

4. Example
 Δ Population = (B - D) + (I - E)
= (25 -17) + (12-9)
= 11 ∴Increased
 Population in 1 year= 526 + Δ population
= 526 + 11
= 537
 Population in 4 years = 526 + 4 x Δ Population
= 526 + 4 x 11
= 570