Species have different reproductive patterns that can help enhance
their survival.
• High reproductive rate (r) : r-selected species
These species usually have many small offspring, and give them little or
no parental care.
They overcome potential
offspring loss by producing so
many.
r-selected species do relatively
well in unstable or unpredictable
environments.
Other r-selected Traits Include:
• early maturity onset
• short generation time
Organisms whose life history is subject to r-selection are often referred
to as r-strategists.
• bacteria and diatoms,
• insects
• weeds
• semelparous cephalopods
• some mammals
• reptiles
What exception to the
rule do mammals exhibit,
that none of the other
groups do?
They nurture and care
for their young for an
extended period of time.
Semelparity and iteroparity are two
reproductive strategies.
In stable or predictable environments, K-selection predominates as the
reproductive strategy.
Unlike r-selected populations, where population size can change
dramatically overnight, K-selection populations are typically close to the
maximum that the environment can bear (carrying capacity) at most
times.
The ability to compete successfully for limited resources is crucial for
that reason.
K-Selected Traits Include:
• Large body size
• Longer life expectancy
• Fewer offspring
• Extensive parental care
Although some organisms are identified as
primarily r- or K-strategists, the majority
of organisms do not follow this pattern.
• Trees have traits such as large size,
longevity and strong competitiveness that
characterize them as K-strategists.
• In reproduction, however, trees typically
produce thousands of potential offspring
and disperse them widely, traits
characteristic of r-strategists.
• Sea turtles display both r- and K-traits:
although large organisms with long
lifespans (should they reach adulthood),
they produce large numbers of unnurtured offspring. As mentioned earlier,
mice appear to be “r” selected, but the
nurturing nature of mammals is more of a
“K” selected trait.
Define and give an example of an “r”-selected species.
What type of advantage does being an “r”-selected species
give you in an environment?
Define and give an example of a “K”-selected species.
What type of advantage does being a “K”-selected species
give an organism in an environment?
How would being semelparous give you an advantage in an
environment?
How would being iteroparous give you an advantage in an
environment?
Country A
Country B
144
82
Crude Birth Rate
43
8
Crude Death Rate
18
10
Infant Mortality Rate
100
3.8
Total Fertility Rate
5.9
1.3
Percentage of population under 15 years
old
45
14
Percentage of population older than 65
3.0
19
Average life expectancy at birth
47
79
Percentage Urban
44
75
Population in Millions
What are “crude” birth and death rates?
Crude birth rate is the number of childbirths per 1,000 people
per year (in estimation)…and crude death rates, similarly, are the
number of deaths per 1,000 people per year.
For example, if a country has a population of one
million and 15,000 babies were born last year in that
country, we divide both the 15,000 and 1,000,000 by
1000 to obtain the rate per 1000. Thus the Crude
Birth Rate is 15 per 1000.
The Crude Birth Rate is called "crude" because it does
not take into account age or sex differences among
the population. In our hypothetical country, the rate
is 15 births for every 1000 people but the likelihood is
that around 500 of those 1000 people are men and of
the 500 who are women, only a certain percentage are
capable of giving birth in a given year.
Crude Birth Rates of more than 30 per 1000 are
considered high and rates of less than 18 per 1000 are
considered low. The global Crude Birth Rate in 2012
was 20.3 per 1000.
In 2012, Crude Birth Rates ranged from 8.33 per 1000
in Germany to 50.66 in Niger. The CBR in the United
States in 2012 was 13.68 per 1000.
World historical and predicted
crude birth rates (1950–2050)
Years
CBR
Years
CBR
World historical and predicted
crude death rates (1950–2050)
Years
CDR
Years
CDR
1950–1955 37.2 2000–2005 21.2
1950–1955 19.5 2000–2005
8.6
1955–1960 35.3 2005–2010 20.3
1955–1960 17.3 2005–2010
8.5
1960–1965 34.9 2010–2015 19.4
1960–1965 15.5 2010–2015
8.3
1965–1970 33.4 2015–2020 18.2
1965–1970 13.2 2015–2020
8.3
1970–1975 30.8 2020–2025 16.9
1970–1975 11.4 2020–2025
8.3
1975–1980 28.4 2025–2030 15.8
1975–1980 10.7 2025–2030
8.5
1980–1985 27.9 2030–2035 15.0
1980–1985 10.3 2030–2035
8.8
1985–1990 27.3 2035–2040 14.5
1985–1990
9.7
2035–2040
9.2
1990–1995 24.7 2040–2045 14.0
1990–1995
9.4
2040–2045
9.6
1995–2000 22.5 2045–2050 13.4
1995–2000
8.9
2045–2050
10
Discuss projected trends of birth and death rates. What might the
population pyramid for the world population in 2045-2050 look like?
% Growth Rate, or % change, is a useful indicator to look at how much
a population is growing or declining in a particular area. Let’s take a
look at an example:
Calculate the growth rate or % change of a particular city, which had a
population of 800,000 in 1990, and 1,500,000 in 2008:
(
Current Value – Past Value
Past Value
1,500,000 – 800,000
700,000
(
(
800,000
(
So:
(
(
GROWTH RATE:
x 100
x100
x100
800,000
.875 x 100 = 87.5% growth rate
To calculate how that translates to a yearly annual rate, take the total
growth rate, and divide it by the number of years, or
87.5% / 18 YEARS AVERAGE ANNUAL GROWTH RATE = 4.86 %
Total enrollment at Northwest High School as of September 2008 was
3,267. The enrollment at Northwest High School for September 2012
was 2,520. What is the annual growth rate?
Current value: 2,520
(
(
Past Value: 3,267
2,520-3,267
3,267
x 100
-747/3,267 x 100
-.228 x 100 = -22.8%
What is the annual growth rate, if over 4 years the net growth rate is
-22.8%
-22.8%/4 or, -5.7%
Our population is in decline! Don’t start having babies!!!
As of today…our population is 2,453 students. Recalculate, based on
that number.
-4.98%/annum
In the coming years, the fifty least developed nations are expected to
increase their populations greatly, from 800 million to 1.7 billion. What is
the annual growth rate, if this projected increase were to take place
over two decades?
PV
(
x 100
(
(
(
CV-PV
1,700,000,000-800,000,000
800,000,000
x 100
900,000,000 / 800,000,000 = 1.125 x 100 = 112.5%
increase over 20 years
Annual Average = 112.5/20 = 5.625% increase per
annum.
There is another way to calculate the growth rate, and it is the way you
would most likely see it on the AP ES Test. Instead of using actual
birth numbers, and death numbers, you would use the Crude Birth
Rate, and the Crude Death Rate. (CBR and CDR).
To calculate population growth rate using these figures, the formula is
r=CBR-CDR
In 1855, the first year vital statistics were collected for Washington DC,
the total population was 1.6 million, with a crude birth rate of 43/1,000.
The population was growing rather slowly, because of the relatively high
crude death rate of 41/1,000. In 1875 the growth rate increased rapidly,
as the crude birth rate remained at 43/1,000, while the crude death rate
dropped to 20/1,000.
In 1895, the crude birth rate dropped to 37/1,000, and the death rate to
12/1,000. In that year, a census showed that the population of
Washington DC had grown to 2.5 million. By 1950 the population growth
had declined as the cdr remained at its 1895 levels, but the cbr had
dropped to 22/1,000.
In 1977 statistics showed that the cdr was at 10/1,000 and that the
population growth had slowed to .4%. By 1990, Washington DC had
reduced its birth rate to that of its now, low death rate. The
population was in balance.
What was the annual growth rate of Washington DC in 1950?
What was the birth rate in Washington DC in 1977?
Let’s take these questions ONE at a time!
What was the annual growth rate of Washington DC in 1950?
In 1895, the crude birth rate dropped to 37/1,000, and the death rate to
12/1,000. In that year, a census showed that the population of
Washington DC had grown to 2.5 million. By 1950 the population growth
had declined as the cdr remained at its 1895 levels, but the cbr had
dropped to 22/1,000.
r= cbr - cdr
r = 22/1,000 - 12/1,000 = 10/1,000 or
r = 2.2% - 1.2% = 1% or
r = .022 - .012 = .01
The annual growth rate for Washington DC in 1950 was…
As you can see, there are multiple ways
to earn your points!
In 1977 statistics showed that the cdr was at 10/1,000 and that the
population growth had slowed to .4%. By 1990, Washington DC had
reduced its birth rate to that of its now, low death rate. The
population was in balance.
The question is what was the birth rate in Washington DC in 1977?
You know the growth rate is .4%, and you know the CDR is 10/1,000.
You don’t know the birth rate.
So, set up your formula:
r = CBR - CDR
Remember, you get
points for writing the
.4%= cbr – 10/1,000 or
equation, and working
.4% = cbr – 1/100 or
out each step. The
correct answer is only
.4% = cbr - .01 (1%)
worth 1 point, while
So
the process will earn
you more!
.4% = cbr – 1% (solve for cbr)
.4% + 1% = cbr – 1% + 1%
1.4% = cbr
Or 14/1,000
http://www.shodor.org/interactivate/activities/RabbitsAndWolves/
For homework tonight, and over the weekend, proceed to link above,
and complete the simulation in the following manner:
• Determine the original population size by clicking the “view cumulative
stats” button.
cv = current value
• Set the forest size for large
pv – past value
• Set the forest border to island
• Leave the speed alone
• Start the simulation, and time it for 15 seconds. Then pause the
simulation.
• Select “view simulative stats”, and calculate the population growth
rate for both rabbits and wolves during that period of time. Which
formula will you use? r = CBR-CDR or r = cv –pv / pv x 100 ?
• Now resume the simulation two more times, each in 15 second increments.
Calculate new population growth rate of each population after each 15 second
period.
• After each population growth rate calculation, determine two possible factors that
could account for such statistics. Submit all calculations and answers into moodle by
next Monday!