Population Growth

Population Growth
Factors that regulate population size
Population Growth Patterns
• Population Characteristics
– Size
– Density
• number per area
– Distribution
• Uniform
• Random
• Clumped
Population Distributions
Population Characteristics
– Sex ratios
– Age structure
• Number of individuals in different age classes
– Reproductive age
– Pre-reproductive age
– Post-reproductive age
Age Structure Diagrams
Population Growth
•Growth Rate
– Factors that increase population sizes
• Birth Rate (BR)
• Immigration (Im)
– Factors that decrease population sizes
• Death Rate (DR)
• Emigration (Em)
Growth Rate = (BR + ImR) – (DR + EmR)
• Exponential growth
– A stable rate of growth leads to exponential
– As the population size increases, the same
percentage increase becomes a larger total
Exponential Growth in a population
Occurs when a population starts out small and
environmental conditions are ideal.
• Factors that limit Growth
– Physical, chemical and biological factors
(biotic and abiotic) that limit the amount of
• Space
• Nutrients
• Predators
– All limiting factors together make up the
“environmental resistance” and affect the
carrying capacity of the environment
Environmental Resistance determines
Carrying Capacity
Logistic Growth
Curve (S-curve)
Carrying Capacity can change when limiting factors
Limiting Factors
• Shelford’s Law of Tolerance (p. 588)
– Certain range of environmental conditions
that will allow for maximum population
• Density Independent factors affect a
population regardless of its size
– Abiotic factors: climate, space
Limiting Factors
• Density dependent factors
– Population size can limit further population
– Intraspecific competition
• Food resources
• Mates
– Disease
– Interspecific Competition
– Predation
• The study of human populations
– Population Size
– Population Density and Distribution
– Age Structure
– Sex Ratios
Human Population Growth
• Human population growth has been
greater than exponential.
– Growth rate has increased over time (mostly
because of lower death rates).
– Global growth rate peaked at 2.1% in the
Global Human Population
Human Distribution
Effect of Age Structure on Population Growth
Age Structure Diagrams
Age Pyramid for United States
Age structures are very different in the
developed and developing countries
Effect of sex ratios on population growth
What is the earth’s carrying capacity?
• Carrying capacity is influenced by, but not
defined by, environmental impact.
• Environmental impact depends on more
than population alone.
– Technology can increase or decrease the
• Cause more consumption – or –
• Exploit previously unavailable resources
Technological innovations that increased
carrying capacity
Decline in Global Growth Rate
Is growth rate responding to
environmental resistance?
• What part of the growth rate equation is
• Is the change occurring fastest where
resources are scarcest?
• Is the change resulting in less
environmental impact?
TFR correlates with social opportunity
for women
Growth rates are unevenly distributed
Population is increasing fastest where
the standard of living is lowest
Ecological Footprints
The amount of resources used per person can be
expressed in terms of the amount of land needed to
provide those resources
What does the future hold?