How Do Populations Change in Size?

download report

Transcript How Do Populations Change in Size?

How Do Populations
Change in Size?
A population is all the members of a species living in the
same place at the same time.
• A population is a
reproductive group
because organisms breed
with members of their own
– Ex: Daisies in a field in Mt.
Holly will breed with each
other, not with daisies in
Properties of Populations
Properties are used to describe populations and to
predict changes within them
• 1) Population Size
• 2) Population Density – number
of individuals per unit area or
volume (ex: number of trout per
cubic meter of water in a lake)
Flamingos live in clumped flocks
• 3) Population Dispersion – the
relative distribution/arrangement
of its individuals within a given
amount of space (ex: even,
clumped, or random)
Rattlesnakes are randomly dispersed
How Does a Population Grow?
• A population gains individuals with each birth
and loses them with each death.
Growth Rate = Birth Rate – Death Rate
1) What happens to the growth rate if there are more births than deaths?
2) What happens to the growth rate if there are more deaths than births?
How Do Populations Change in Size?
Wild female rabbits can have up to 12 babies per litter (average
Female rabbits can have between 1-7 litters per year (average
1) Theoretically, how many babies could 1 female rabbit birth
in one year?
2) If half of the babies from #1 are female, how many more
baby rabbits could be born the next season?
3) What would happen to the population if these birth rates
4) What happens to keep the population from climbing
84 babies
3528 babies
The population would increase
The environment limits their survival
How Fast Can a Population Grow?
• Reproductive Potential – the maximum number
of offspring that an organism can produce.
– Different organisms have different generation times (the
average time it takes a member to reach reproduction
age) Ex: human vs. bacteria
– RP increases with organisms that produce more
offspring at a time, reproduce more often, and
reproduce earlier in life.
You’re The Big Winner!
• You have just won the grand prize on a
game show! You can choose between two
cash prizes, but you only have 30 seconds to
– Choice #1 - $1000 per day for 30 days with
$500 bonus every 10 days.
– Choice #2 - $0.01 on the first day, which then
doubles every day for 30 days.
Exponential Growth
• Exponential Growth –
increased growth that
gets faster and faster
over time
– Occurs in nature only
when a population has:
• Plenty of food and space
• Little to no competition or
– Occurs regularly in
bacteria and mold growth
Think – Pair - Share
1) How does the curve of
this graph show
exponential growth?
2) What would the graph
look like if it had linear
3) How does exponential
growth relate to
reproductive potential?
Think – Pair - Share
How does the curve of this graph
show exponential growth?
The curve rises more and more steeply,
meaning the population increases by
greater amounts during each time
What would the graph look like if
it had linear growth?
It would show a straight line, increasing
by the same amount during each time
How does exponential growth
relate to reproductive potential?
Most organisms have the potential to
reproduce multiples of themselves, thus
creating exponential growth rates.
Exponential growth shows nearly
unlimited population growth to a point.
Bacteria Colony Growth
• Observe the growth of bacteria.
• Graph the growth.
• 1) Is this growth exponential? Explain.
• 2) Will the bacteria continue to grow at this
rate indefinitely? Why or why not?
What Limits Population Growth?
• Carrying Capacity – the maximum
population that the ecosystem can support
Think About It
• 1) How was the
reindeer population
able to increase so
• 2)Why did the
reindeer population
• 3) How is this related
to carrying capacity?
How does a population reach its
carrying capacity?
– When resources become limited
• Limiting resource – when a resource is consumed at
the same rate as it is being produced by the ecosystem.
– Ex: plant growth is limited by water supplies, mineral nutrients,
and sunlight.
– Competition within a population
• As the population approaches the carrying capacity,
members of the population begin to compete for limited
– Territory – an area defended by one or more individuals
against other individuals because of the space, shelter, food ,
or breeding sites it contains.
Population Regulation
• Population growth is
regulated by deaths
– Density Dependent – death
that happens when individuals
of a population are densely
packed together. Ex: Limited
resources, predation, and
– Density Independent –
deaths that affect all members
of a population in a general
way. Ex: Severe weather and
natural disasters
Diseased trees in a forest
Winter storm froze plants
Favorite Populations
Choose a favorite plant or animal. Write it
Answer the following questions:
1) Where in the world can you find populations of this
2) What kinds of resources are limiting to its growth?
3) How are the individuals dispersed within their
4) How do the organisms find each other to mate?
5) How many offspring do they produce on average?
Nile Perch from
Lake Victoria 
 Cichlid species
that live in Lake