Population Ecology
Population Growth
• The increase in number of individuals in a
population
• Biotic potential is the maximum growth rate a
population can achieve with unlimited
resources
• Why don’t most populations reach biotic
potential?
BECAUSE RESOURCES ARE LIMITED
Growth Curves
• A J-shaped growth curve shows exponential growth of a population
• Exponential growth starts slowly (lag phase) and then increases rapidly (exponential phase)
• Most populations don’t show J-shaped curves – why?
Not enough resources
J-Shaped Growth Curve
Leopard
seal popula
tion
Growth Curves
• An S-shaped curve shows exponential growth
followed by a leveling off of the population
• The leveling off shows the population has
stopped increasing
• Carrying capacity is the maximum number of
individuals an ecosystem can support
• What factors determine the carrying capacity of
an ecosystem?
Food, water, space (resources)
S-Shaped Growth Curve
• Why does the
population level off
over time?
• What is the leveling
off phase called?
S-Shaped Growth Curves
Time (hours)
Carrying capacity
Growth Curves
• A sawtooth curve shows
the relationship between
predator and prey
populations
• Why is the hare
population always larger
than the lynx
population?
Growth Curves
• A boom-and-bust
curve shows
exponential growth
followed by a drop-off
of the population
• What might cause a
population to
decrease rapidly?
– Seasons or
destruction of habitat
Limits on Growth
• Population density is the number of individuals in
a population in a certain area
• Which has a higher population density - New
York City or Antarctica?
• Density-dependent factors limit growth when the
population reaches a certain density
• Density-independent factors limit growth
regardless of the density
Limits on Growth
Classify the list below as density dependent
or density independent limiting factors
• Disease
• Competition for food
• Limited habitat
• Tornado
• Seasonal temperature changes
• Forest fire
Limits on Growth
• Classify the list below as density
dependent or independent factors:
Dependent Independent
Disease
Tornado
Competition for food
Limited habitat
Seasonal weather changes
Forest fire
Ecosystem Relationships
• Competition occurs when individuals
require the same limited resources in an
ecosystem
• Predator-prey relationship occurs when
one organism feeds on another
• Symbiosis is a close relationship between
two different species
Types of Symbiotic Relationships
• Mutualism is a relationship in which both
organisms benefit
• Commensialism is a relationship in which
one organism benefits and the other is
neither helped nor hurt
• Parasitism is a relationship in which one
organism benefits and the other is hurt
– The parasite benefits and the host is the
hurt
Summary of Symbiotic
Relationships
Relationship Species 1 Species 2 Example
Mutualism
Commensialism
Parasitism