Transcript POPULATIONS JIGSAW ACTIVITY

Question
• Would you rather be paid $100 a day for a
month or 1 penny the first day, 2 pennies
the second day, 4 pennies the next day, 8
pennies the next day…etc. for the rest of
the month?
• EXPLAIN YOUR ANSWER
• $100 a day equals $3,000 for the month.
• Starting with one penny, two pennies on
the second day, 4 on the third day, 8 on
the fourth day, etc.
• 1x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2
x2x2x2x2x2x2x2x2x2x2x2x2=
Population Growth
• I will call on a student to give me a
beginning population (# between 10-1000)
• I will call on another random student to
give me a birth rate (Crude birth rate is the
number of births per year per 1000 adults)
(# between 5-40)
• We’ll put the data into a spread sheet to
see what kind of growth occurs
• population growth.xls
Exponential Model of Population Growth
• Population increases rapidly with no limit
• What will a graph look like? “J” shaped curve
• Rare in nature. Why?
Limit on the amount of resources (food / space)
limiting factors
• Populations can’t grow exponentially
forever because of limiting factors.
• Limiting Factors can be:
BIOTIC– predators, food availability,
disease, competition from their own
species
ABIOTIC– space, water, shelter, nutrients,
salinity, temperature.
How populations change
INCREASE size DECREASE size
• Births
• Immigration
(coming in)
• Deaths (mortality)
• Emigration
(going out/leaving)
•
Growth rate = (births + immigration) – (deaths + emigration)
•
•
•
If (births + immigration) > (deaths + emigration), population INCREASES
If (births + immigration) < (deaths + emigration), population DECREASES
If (births + immigration) = (deaths + emigration), population stays the same
logistic growth
AKA “S-curve” or sigmoidal
• More realistic model than exponential.
• Populations reach carrying capacity.
Carrying capacity- the number of individuals
the environment can support over a long
time period
What alters the carrying capacity of an
environment?
Logistic Model of Population Growth
When at carrying capacity,
birth rate is equal to
• Accounts for influence
death rate
of limiting factors
• What
will the graph
As population
reaches
look carrying
like? capacity,
the difference between birth
rate and death rate decreases
“S”
WhenStretched
populationout
is small,
birth rate is higher
than death rate
Wrap Up
In the Oh Deer activity we learned about
biotic and abiotic factors, how they are
part of an ecosystem and how they
influence the deer population.
In a sentence or two, explain (in general
terms) what a limiting factor is and its
effect on a population.