Download FACTORS AFFECTING POPULATION CHANGE

Factors Affecting Population Change
A. Density-dependent factors limit
population growth and intensify as the
population increases in size (i.e.
Competition for resources, disease...)
Density-dependent factors
1. Intraspecific competition is when
individuals of the same species compete
for resources. If this is high then the
population will have a low growth rate.
Density-dependent factors
2. Predation is the consumption of prey by
a predator. If there is more prey available
they will be chosen more by predators.
Density-dependent factors
3. Allee effect: Warder Allee found that
some density-dependent factors reduce
population growth when the population is
at a low density rather than high density.
 Ex. harder for individuals to find a mate and
successfully reproduce thus lowering the
growth rate of species.
Allee-effect continued
 Small populations also may go through
inbreeding depression which reduces the
populations' genetic variability and may
prevent successful population growth.
Allee-effect continued
 The minimum viable population size is
the smallest number of individuals that
ensures the population will persist for a
certain period of time.
 Allows biologists to determine whether a
species is endangered.
Factors Affecting Population Change
B. Density-independent factors limit
population growth no matter what the
population size
 i.e. Natural disaster, human
intervention...
Density-independent factors
 The resource in the ecosystem that is in
the shortest supply is known as the
limiting factor since it is preventing
massive population growth.
Population Change Affects the Entire
Ecosystem
 A change in one
population of species
can affect the entire
hierarchy of living
things in that
ecosystem.

Ex. The disappearance
of beaver from this
ecosystem causes a
decrease in the wolf
population which would
cause an increase in its
other prey