1.Review When do populations grow
exponentially
Apply Concepts Why does exponential growth
show a characteristic J-shaped curve
2.Review What is the characteristic shape of a
logistic growth curve
Explain Describe when logistic growth occurs
Form a Hypothesis What factors might cause the
carrying capacity of a population to change.
CH 5 POPULATIONS
5.1 How Populations Grow



In the 1950s, a fish farmer in Florida tossed a few
plants called hydrilla into a canal
Today, their tangled stems snag boats in rivers and
overtake habitats; native water plants and animals
are disappearing
Why did they get out of control and what can be
done.
Populations


A group of interbreeding individuals of the same
type that live in a particular area
Needed to define
 Type
of individual
 Time
 Place.
Geographic Range


Area inhabited by a population
Range can vary greatly.
Density and Distribution

Population Density
 The

number of individuals per unit area
Distribution
 How
individuals are spaced out across the range:
randomly, uniformly, or clumps.
Random Distribution

Wild flowers grow randomly in a field.
Uniform Distribution

King penguins or a tree farm.
Clumped Distribution

School of fish or pack of wolves.

Population density
 Number

of individuals of a species / (divided by) area
Dispersal
 Organisms

Open population
 Individuals

spreading out to other area
can come and go as they wish
Closed population
 Individuals
must stay within the population.
How do you find the population size
Counting Individuals

Works well for

Limitations
 Large
areas
 Similar looking organisms
 Large or small numbers
 Organisms often don’t stand still while you count.
Sampling Nonmoving Populations
3 Steps
 Find number of individuals in many smaller
areas
 Find the population
density
 Multiply by the area.

Nonmoving Population Example



Number of Ponderosa pines in 100,000 acre section
of Yellowstone National Park
Plot 1: 20 trees in 1 acre; Plot 2: 10 trees in 1 acre;
Plot 3: 30 trees in 1 acre
Number of trees in sampled area
60 trees in 3 acres
= 20 trees per acre

Total number of trees = average density X area
20 trees per acre X 100,000 acres
= 2,000,000 trees.
Nonmoving Population Example 2



Number of Ponderosa pines in 100,000 acre section
of Yellowstone National Park
Plot 1: 150 trees in 3 acres, Plot 2: 90 trees in 1.5
acres, Plot 3: 60 trees in .5 acre
Number of trees in sampled area
150+90+60 = 300 trees
3+1.5 +.5= 5 acres
300 trees per 5 acres = 300/5 = 60 trees per acre

Total number of trees
60 trees per acre X 100,000 acres = 6,000,000 trees.
Sampling Moving Populations



Capture Recapture method, catch recatch, tagging
Catch a number of individuals from the population,
tag them, record the number of tagged individuals,
then release them
Later (time depends on specie) go back to same
area and catch individuals, record the total number
caught AND the number that you tagged earlier.
Moving Populations Example




How many Walleyes are in Howard Lake
Catch, tag, and release 50 walleyes then a week
later catch 60 walleyes, 20 of which are tagged
How many walleyes in the lake
Use Ratios and cross multiple.
Number caught
and tagged
---------------------Total number
=
Number caught second
time that are marked
----------------------Total number caught
the second time
50 walleyes caught
1st time
---------------------Total number of
walleyes in the lake
=
20 tagged walleyes
that were recaught
----------------------60 walleyes caught
the second time
50 x 60 / 20 = 3000/20
= 150 Walleyes in the lake.
Moving Populations Example 2



How many Rainbow Trout are in a 2 mile section of
the Madison River
First time with an electrofisher you catch, clip the
adipose fin, and release 100 fish
Second time you get 20 fish 5 of which were
marked.
100 trout caught
1st time
---------------------Total number of
trout in the river
=
5 tagged trout
that were recaught
----------------------20 trout caught
the second time
100 x 20 / 5 = 2000/5
= 400 trout in that section of river.
Capture Recapture

Downfalls
 Electrofisher
 Catch
them all
 Technique
 Injuries
 Length of time between catches
 Length of time trying to catch.
Population Growth


Tells you if population is growing or not
Four rates affect the population size
 Mortality
 Natality
 Emigration
 Immigration.
Birthrate and Death Rate

Mortality
 Death
rate, population
decreases

Natality
 Birth
rate, population
increases.
Immigration and Emigration

Immigration
 Individuals
move In,
population increases

Emigration
 Individuals
leave, Exit,
population decreases.
Age Structure


The number of males and females of each age a
population contains
Helps to determine population growth.
Exponential Growth
The larger a population gets, the faster it grows
 Requires unlimited resources
 Cannot
continue
 Creates a
J Curve.


Organisms in a new environment can grow
exponentially for a time.
Logistic Growth



Population’s growth slows and then stops after a
period of exponential growth
Happens in natural populations
S Curve.
Phase 1



Exponential growth
Resources are unlimited, rapid reproduction
Low mortality.
Phase 2


Growth slows down
Due to high population size and less resources.
Phase 3


Growth stops
Population will remain at or near this size
indefinitely.
Analyzing Data
Suppose that a pair of rabbits produces six
offspring: 3 male and 3 female and that now
offspring die
Calculate If each pair of rabbits breeds only once
how many offspring would be produced each year
for five years
Interpret Graphs Construct a graph of your data.
What type of growth is occurring?

Growth Rate

May go up (+) or down (-)
Growth rate = (Natality + Immigration) – (Mortality
+ Emigration)

What is a good growth rate.

Growth Rate Example




Start off with 50
elk
You have 20 elk
calves born
You have 4 die of
old age
You have 3 that
jump the fence
and escape

What was your
growth rate for
the year.
Carrying Capacity

The largest population an area can support forever
without harming the environment.