Download Population Dynamics

Population Dynamics
Part 2
Population Ecology: Population Characteristics
Population Characteristics
1. Population Density:
–
The number of organisms per unit area
2. Spatial Distribution:
–
–
Dispersion: The pattern of spacing a population
within an area
3 main types of dispersion
•
•
•
–
Clumped
Uniform
Random
The primary cause of
dispersion is resource
availability
Population Ecology: Population Characteristics
Population Limiting Factors
3. Population growth rate
– How fast a given population grows
– Factors that influence this are:
•
•
•
•
birth rate)
Natality (____
death rate)
Mortality (_____
Emigration (the number of individuals moving
_________
away from a population)
moving to a
Immigration (the number of individuals _________
population)
Population Ecology: Density-independent factors
Population Limiting Factors
• Density-independent factors
– Factors that limit population size, regardless of
population density.
– These are usually abiotic factors
– They include natural phenomena, such as weather
events
• Drought, flooding, extreme
heat or cold, tornadoes,
hurricanes, fires, etc.
Population Ecology: Density-dependent factors
Population Limiting Factors
• Density-dependent factors
– Any factor in the environment that depends on
the number of members in a population per unit
area
– Usually biotic factors
– These include
•
•
•
•
Predation
Disease
Parasites
Competition
Population Ecology: Population Growth Rate
Understanding Exponentials
• Put your pens down for a minute & think about
this:
– An employer offers you two equal jobs for one hour
each day for fourteen days.
– The first pays $10 an hour.
– The second pays only 1 cent a day, but the rate
doubles each day.
– Which job will you accept?
Population Ecology: Population Growth Rate
Understanding Exponentials
Job 1
90
80
70
60
50
40
30
20
10
0
Job 2
Now, how much would
your employer owe you if
you stayed at this job for
another 2 weeks?
Job 2 lags for a long
time before
exponential growth
kicks in!
1
2
3
4
5
What would happen if this
type of growth took place
within a population?
6
7
8
9
10 11 12 13 14
Population Ecology: Population Growth Rate
Population Limiting Factors
• Population growth models
– Exponential growth model
•
•
•
•
•
Also called geometric growth or J-curve.
First growth phase is slow and called the lag phase
Second growth phase is rapid and called the
exponential growth phase
Bacteria can grow at this rate, so why aren’t we up to our
ears in bacterial cells?
Population Ecology: Population Growth Rate
Population Limiting Factors
• Population growth models
– Limits to exponential growth
• Population Density (the number of individuals per unit of
land area or water volume) increases as well
• Competition follows as nutrients and resources are used
up
• The limit to population size that a particular environment
can support is called carrying capacity (k)
– When you’re done writing, put your pens down…
Population Ecology: Population Growth Rate
What population do you think this is?
So, what do you think is going to happen to
the human population?
• We will probably reach our carrying capacity.
• Our growth rate will start to look like most
organisms, which is the Logistic Growth Model
Carrying Capacity (k)
What letter does this curve
kind of look like?
Population Ecology: Population Growth Models
Population Limiting Factors
• Population growth models
– Logistic Growth Model
• Often called the S-shaped growth curve
• Occurs when a population’s growth slows or stops
following exponential growth.
• Growth stops at the population’s carrying capacity
• Populations stop increasing when:
– Birth rate is less than death rate
(Birth rate < Death rate)
– Emigration exceeds Immigration
(Emigration > Immigration)
Population Ecology: Population Growth Models
Population Limiting Factors
•
Population growth models
– Logistic Growth Model
The S-curve is not as pretty as the image looks
1. Carrying capacity can be raised or lowered. How?
Example 1: Artificial fertilizers have raised k
Example 2: Decreased habitat can lower k
2. Populations don’t reach k as smoothly as in the logistic
graph.
•
•
Boom-and-Bust Cycles
Predator-Prey Cycles
Population Ecology: Reproductive Strategies
Population Limiting Factors
•
Species that follow this pattern
usually
1.
2.
3.
4.
Have a Boom-and-Bust Life Cycle
Have short life spans
Produce many offspring
Smaller organisms
•
5.
6.
•
i.e., fruit flies, mice, locusts
Don’t maintain a population near
carrying capacity
Controlled by densityindependent factors
They are called r-strategists (for
rate of increase)
Population Ecology: Reproductive Strategies
Population Limiting Factors
•
Species that follow this
pattern usually
1.
2.
3.
Have long life spans
Produce few offspring that
have a better chance of
living to a reproductive age
Are larger organisms
•
4.
5.
•
i.e., elephants
Maintain a population at or
near k
Controlled by densitydependent factors
They are called kstrategists (for karrying
kapacity)