Download Populations - Fall River Public Schools

Populations
How Populations Grow
Objectives
• Identify the 3 characteristics of a
population.
• Identify the 3 factors that affect a
population‟s growth.
• Distinguish between exponential and
logistic growth.
• Define carrying capacity.
Characteristics of Populations
1. Geographic distribution – the total area
inhabited by a population
• Also called range
2. Population density – the number of
individuals per unit area
• Number of individuals ÷ Area
3. Population growth – an increase or
decrease in a population
Population Growth
• 3 Factors that Affect a Population‟s
Growth
1. Birthrate – number of births
2. Death rate – number of deaths
3. Number of individuals that enter or leave a
population
•
•
Immigration – the movement of individuals into
an area
Emigration – the movement of individuals out of
an area
Growth Curves
• A growth curve is a
graph showing the
number of individuals
in a population over
time
Exponential Growth
• Exponential growth –
individuals in a
population reproduce
at a constant rate
•
•
•
Shown on a J-curve
Only occurs under
ideal conditions with
unlimited resources
Shows the biotic
potential of a
population
Biotic Potential
•
Biotic potential – the rate at which a population will grow
if all individuals survive and reproduce at maximum
capacity
•
•
•
•
can only happen when individuals are placed in an ideal
environment with unlimited resources and space and without
hazards such as disease and predators
does not naturally occur
usually only occurs when a species is reintroduced to a habitat
with no other competing species
• only lasts for a short period of time (ex: trout reintroduced to
a lake with no fish)
populations become stable (no large growths or declines) when
there is a balance between the number of individuals and the
J-Curves
•
•
Lag phase – little or no
increase in population
growth
Exponential phase –
population increases
rapidly
• Number of
individuals doubles
rapidly in a specific
time interval
• Population keeps
doubling in shorter
periods of time
Logistic Growth
• Logistic growth – a
population‟s growth
slows or stops
following a period of
exponential growth
•
•
Shown on a S-curve
Occurs as resources
become less
available
Carrying Capacity
• Carrying capacity – maximum number of
individuals an ecosystem is capable of supporting
•
•
•
•
Usually represented by „K‟ on a graph
Can be found on an S-curve graph on the flat line
after the exponential growth ends
Stable populations fluctuate near the carrying
capacity
Fluctuations become more radical in an unstable
environment (ex: blizzards and other natural
disasters)
Notes Review
• Identify the 3 characteristics of a
population.
• Geographic distribution
• Population density
• Population growth
Notes Review
• Identify the 3 factors that affect a
population‟s growth.
• Birth rate
• Death rate
• Immigration/Emigration
Notes Review
• Distinguish between exponential and
logistic growth.
• Exponential growth – individuals in a
population reproduce at a constant rate
• Logistic growth – a population‟s growth
slows or stops following a period of
exponential growth
Notes Review
• Define carrying capacity.
• Carrying capacity – maximum number of
individuals an ecosystem is capable of
supporting
Populations
Limits to Growth
Objectives
• Define “limiting factor.”
• Distinguish between density-dependent
limiting factors and density-independent
limiting factors.
Limiting Factors
• Limiting factor – a
factor that causes a
population‟s growth
to decrease
• Examples:
•
•
•
•
•
Competition
Predation
Parasitism & disease
Drought & other climate
extremes
Human disturbances
Density-Dependent Factors
•
Density-Dependent
Factor – a limiting factor
that depends on
population size
• Have a greater effect
when a population is
large and dense
• Examples include
competition,
predation,
parasitism, and
disease
Competition
• When populations become crowded,
organisms compete with one another for
food, water, space, sunlight (plants), and
other resources
• Interspecific competition – 2 or more
different species compete for the same
resources
• Intraspecific competition – individuals that
are the same species compete for the same
resources
Interspecific Competition
Intraspecific Competition
Predation
• Predation – the hunting of prey for food
• Predator-Prey Relationship – a method of
population control in which a population is
regulated by predation
•
•
•
•
•
When there‟s not a lot of predators, prey populations
increase
When prey populations increase, predator
populations increase because there‟s more prey to eat
Then prey populations decline due to predation
Predator numbers decline due to lack of prey
The cycle then repeats
Predation
Parasitism and Disease
• Parasites steal
nourishment from the
organism they are in,
weaken it, and can
kill it or cause disease
•
Examples: some
types of bacteria,
tapeworms
Parasitism and Disease
Density-Independent Factors
• Density-Independent Factors – factors that
affect all populations, regardless of
population size
• Can cause population crashes
• Usually abiotic factors
• Examples:
• Extreme weather or climate
• Natural disasters (earthquake, tidal wave, tornado)
• Drought
Notes Review
• Define “limiting factor.”
• Limiting factor – a factor that causes a
population‟s growth to decrease
Notes Review
• Distinguish between density-dependent
limiting factors and density-independent
limiting factors.
• Density-Dependent Factor – a limiting factor
that depends on population size
• Density-Independent Factors – factors that
affect all populations, regardless of
population size