Download Populations 1 - ScienceWithMrShrout

Populations 1
Mr. Shrout
3 Important Characteristics to a
Population
1. Geographic Distribution- area inhabited by a
population
–
Cm3- km2
2. Population Density- the number of individuals per
unit of area
–
–
–
Smaller organisms- higher densities
Larger organisms- lower densities
Ex. 25.1 deer/mi2 in PA
3. Growth Rate- change in the number of individuals
over time
–
–
–
Positive= growing
Negative= shrinking
Zero= constant
Distribution Patterns
Even Dispersal
Random Dispersal
Clumped Dispersal
Population Size
• How can you change the size of a population?
– Add:
• Births: new individuals are added to the population
through reproduction
• Immigration: movement of individuals into an area
– Animals arrive in new habitat etc..
– Decrease:
• Deaths: old individual dies
• Emigration: movement of individuals out of a
population
– Young leave an area as they mature…
What determines
population growth rate?
• Population growth rate – change in population
size per unit of time
• Births + immigration  increase population
• Deaths + emigration  decrease population
• Population growth rate = ((birth+immigration
rate) – (death+emigration rate))/ time
Growth Patterns
• Exponential Growth- individuals reproduce at
a constant rate. This occurs under “ideal
conditions” with unlimited resources
– No predation, unlimited food, unlimited space
– Ex. Organisms that reproduce asexually- bacteria
– This growth pattern creates a J-shaped curve
Exponential Growth
• Rememberunlimited
resources
• Reproducing at
maximum rate
Growth Patterns
• Exponential growth never lasts for very longthe environment cannot support it.
• Logistic Growth- populations growth slows or
stops as resources become less abundant
– How: Births decrease, deaths increase,
immigrations decrease, emigrations increase
– This is the pattern most often observed
Logistic Growth
• Creates an S-shaped
curve
• Carrying Capacity (K):
The point around which
the growth line
becomes flat (growth
rate= 0) represents the
largest number of
individuals that
environment can
support
K is a hard thing to reach
As Environment Changes, so does
carrying capacity
Factors that affect populations
• What aspects of the ecosystem can limit the
population of a species?
• Anything that changes the relationship between births,
deaths, immigrations and emigrations will change the overall
population size.
• A limiting factor = a factor that causes population growth to
decrease
• Some limiting factors include:
–
–
–
–
–
–
Access to resources
Competition
Predation
Parasitism and disease
Drought and other climate extremes
Human disturbances
Limiting Factors
• There are 2 main categories of limiting factors:
– Density-dependent factors- factor that depends
on the size of the population to act
– Density-independent factors- affect all
populations in similar ways, regardless of
population size
Density-Dependent Factors
• A limiting factor that depends on population size including:
– Intra and interspecific Competition – organisms struggle for resources
– Predation – predator-prey relationship controls population of both the
predator and the prey
– Parasitism – control population by weakening/killing host. Less hosts=
less parasites as well.
– Disease - control population by weakening/killing host
• Density dependent factors become limiting only when the
population density (number of organisms per unit area)
reaches a certain level
• These factors operate most strongly when a population is
large and dense
Competition
• As resources become more scarce competition
for that resources increases
• With greater competition, there is a larger
struggle for survival
• It becomes more likely that a given individual
will not succeed.
Intraspecific Competition
Predator-Prey Relationship
• The number of predators and prey in a system are directly related
–
–
–
–
Predators increase- Prey decreases
Prey decreases- predator decreases
Predator decreases- prey increases
Prey increases- predator increases
Disease
Density-Independent Factors
• Affect all populations in similar ways, regardless of the
population size including:
–
–
–
–
Unusual weather
Natural disasters
Seasonal cycles
Human activities (damming rivers/clearing forests)
• Many species will show a characteristic “crash,” then the
population will build back up right away, or stay low for some
time
• Environments are always changing, and most populations can
adapt to a certain amount of change by growing or shrinking
in size.
• Major upsets in the ecosystem can lead to long-term declines
in certain populations (human activities)
Density Independent- Extreme
Weather
Seasonal
Human Activities
Overexploitation of cod fishery- grand banks