Populations and
Limits to Growth
Population Density and Dispersion
• Population Density: a measurement of the number of individuals
living in a defined space
• Example: rural area vs. city
• Population Dispersion: the way individuals in a population are
spread in an area
• Clumped dispersion: live close together
• Uniform dispersion: live at specific distances from each other
• Random dispersion: individuals spread randomly
Population Growth
• Affected by:
•Number of births (increase)
•Number of deaths (decrease)
•Number of individuals that enter (immigrate)
or leave (emigrate) a population
•Immigration: movement of individuals into an
area
•Emigration: movement of individuals out of
an area
Exponential Growth
• Occurs when the
individuals in a population
reproduce at a constant
rate
•Occurs under ideal
conditions with unlimited
resources
Logistic Growth
• Occurs when a population’s growth
slows or stops following a period of
exponential growth
• Most common type of growth
• As resources become less available,
the growth of a population will slow or
stop
• Reaches carrying capacity: largest
number of individuals that a given
environment can support
Limits to Growth
• Limiting factors: factors that cause a populations
growth to decrease
•Competition
•Predation
•Parasitism and disease
•Drought and other climate extremes
•Human disturbances
Density-Dependent Factors
•Limiting factors that depends on
population size
•Affect mostly large populations
•Do not really affect small, scattered
populations
•Include: competition, predation,
parasitism and disease
Density-Independent Factors
• Limiting factors that affect all
populations in similar ways, regardless of
population size
•Unusual weather, natural disasters, seasonal
cycles, human activities