Download Population Size Time (millions) (seconds)

Population Biology
Population Biology Questions
• What is a population?
• Describe how populations grow.
• What is the difference between an S shaped
curve and a J shaped curve?
• What is a life history pattern?
• Describe the two types of life history patterns.
• What is the difference between densitydependent and density-independent limiting
factors?
Principles of Population Growth
• What is a population?
– A group of organisms that are of the same species
and live in the same area
• How do populations grow?
How Do Populations Grow?
• Population growth is not linear:
In linear growth,
the population
grows by adding
a fixed amount
each time period
Ex: Every minute, 5
individuals are added to
the population
How Do Populations Grow?
• Population growth is not linear.
• Population growth can be exponential.
-Exponential
growth indicates
that as a
population gets
bigger, it also
grows at a faster
rate
How Do Populations Grow?
• Population growth is not linear.
• Population growth can be exponential.
– Exponential growth can be J shaped or S shaped
-J shaped curves have no upper limit so they continue to grow
forever. S Shaped curves have an upper limit so they stop
growing and level off at some fixed point
What limits growth on an S shaped
population curve?
• Carrying capacity: the number of organisms of
one species that an environment can support
Where are birth
rates higher than
death rates?
Where are birth
rates and death
rates the same?
Where are death
rates higher than
birth rates?
Principles of Population Growth
• What is a population?
– A group of organisms that are of the same species
and live in the same area
• How do populations grow?
– Not linear
– Exponential
• J shaped
• S shaped
– Carrying capacity
Graph this.
Population SizeTime
(millions)
(seconds)
2
10
6
20
8
30
15
40
33
50
59
60
Reproductive Patterns
• Why don’t populations reach carrying capacity
and remain stable?
– To answer this question we have to study lifehistory patterns
– Life-history pattern: an organism’s reproductive
pattern
Life History Patterns
• Rapid life history pattern: population
increases rapidly, then declines when there
are sudden environmental changes
• Organisms with rapid life-history patterns are
usually small and have a short life span
Life History Patterns
Slow life-history pattern: individuals reproduce
and mature slowly and have a long life span
– Population sizes are maintained at or near
carrying capacity
Density factors and population growth
• There are three patterns of population
dispersal:
Density factors and population growth
• There are three patterns of population
dispersal: clumped, spaced, and random
• There are two kinds of limiting factors that
affect population dispersal:
– Density independent factors: limiting factors that
affect population size regardless of their density
• temperature, storms, floods, habitat disruption
– Density dependent factors:
• disease, parasites, or food availability
Reproductive Patterns
• Why don’t populations reach carrying capacity
and remain stable?
– It depends on whether they have a rapid or slow
life history pattern, and it depends on the
combination of density dependent and
independent factors that are around
Organism Interactions that Limit
Population Size
• Predation
• Competition
• Density
– Effects of crowding and stress
Principles of Population Growth
• What is a population?
– A group of organisms that are of the same species and
live in the same area
• How do populations grow?
– Linear vs exponential (J vs S shaped)
• Reproduction Patterns
– Life history patterns (rapid vs slow)
– Density dependent vs Density independent limiting
factors
• How do organisms affect population size?
– Predation, competition
Population Biology Questions
• What is a population?
• Describe how populations grow.
• What is the difference between an S shaped
curve and a J shaped curve?
• What is a life history pattern?
• Describe the two types of life history patterns.
• What is the difference between densitydependent and density-independent limiting
factors?