UNIT 3
Chp 5.1 and 5.2
Population Growth
5.1 How populations
grow
 Population – a group of organisms of a
single species that lives in a given area.
Researchers study populations’ geographic
range, density and distribution, growth
rate, and age structure.
Geographic Range
 The area inhabited by a
population.
 Can vary greatly in size
Geographic range of the
American Chestnut
Population Density
 Number of individuals per unit area.
Random
Uniform
Clumped
Population Growth
 Factors that affect population size are the
birthrate, death rate, and the rate at which
individuals enter or leave the population.
 Populations can grow if more
individuals are born than die in any
period of time.
Population Growth
 Immigration- when a population grows if individuals
move into a given area.
 Emigration- when a population decreases in size due
to individuals leaving the area.
 Exponential Growth- under ideal conditions with
unlimited resources, a population will grow
exponentially.
 Logistical Growth- occurs when a population’s
growth slows and then stops, following a period of
exponential growth.
Exponential Growth
Logistic Growth
 K is the
Carrying
Capacitymax # of
individuals
of a species
that an
environment
can support.
5.2 Limits to Growth
 Limiting factors determine the carrying
capacity of an environment for a species.
 Density-Dependent Factors-include
competition, predation, herbivory, parasitism,
disease, and stress from overcrowding. They
only act on dense populations, not small
scattered ones.
Density-Independent
Limiting Factors
 Unusual weather, hurricanes, droughts,
wildfires, floods, can cause a population
to “crash” and then slowly build back up
over time.
Invasive Species
 A non-native species introduced into an
area (usually be humans).
 Many invasive species will overpopulate
an area a take up resources from native
species.
Purple Loosestrife
Asian Longhorn Beetle