Population Growth
385-388
Models of Growth
•Growth rates of a population can be determined by looking
at birth and death rates
•Growth Rate = ______births – deaths_______
# of individuals in the population
Growth Rate Practice
•There were 37 births and 20 deaths in a seal population of
300 last month
•Growth rate = 37-20 = 0.057 last month
300
• Population is increasing in size
Growth Rate Practice
•25 births per 200 sea otters in one week
•75 deaths per 200 sea otters in one week
•Growth rate = 25-75 = -.25 per week
200
• Population is decreasing in size
Exponential Growth (J-shaped curve)
•Type of growth that shows slow growth at first, followed by
increasingly faster rates of growth
•Birth and death rates are constant, births are higher than
deaths
•Limited by density-independent factors
Exponential Growth
•Ex. Bacterial growth
Logistic Growth (S-shaped)
•Population growth starts out fast as there are more births
than deaths
•Slows down, then levels off when the carrying capacity (K)
is reached
• (K): the number of individuals the environment can support
over time
•Limited by density dependent factors
Logistic Growth
•Most organisms follow this type of growth
Regulating Population Growth
•Limiting factors: restrains population growth
• Density-independent factors: no regard for population density
• Limits exponential growth
• Examples: Weather, seasons, natural disasters
Regulating Population Growth
•Density-dependent factors: increase or become more
prominent when the population density increases
• Limits logistic growth
• Ex. Predation, pollution, food storage, crowding