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