Download CH 43 Populations Notes - Lincoln Park High School

POPULATIONS
Chapter 43
Populations intro
What is a population?
Why do humans study
populations? Why
would we want to
influence the
population size of
different species?
43.1 Populations Are Patchy in Space and Dynamic over Time


Abundance is measured by population density (number
of individuals per unit area) and population size
 Populations are usually dispersed in habitat patches –
“islands” of suitable habitat separated by areas of
unsuitable habitat
 Populations are dynamic (always changing) and
interdependent
Life history—description of an organism’s life cycle
Females
emerge in
spring, lay
eggs, and die
Life
Cycle:
Blacklegged
ticks
Survivors
seek host
Mated
females
overwinter
Seek large
mammal
host & mate
Winter
dormancy
(9/28) BR
1. Explain how the population shifts seen below demonstrate that
the lynx and hare populations are interdependent. How does each
influence the other?
2.
3.
Explain how the three populations shown in the graph below are interdependent.
Ticks are a vector for Lyme disease. How might the information depicted in the
graph below be used to reduce the probability of getting Lyme disease?
43.3 Life Histories Determine Population Growth Rates

Life tables shows ages at
which individuals make life
cycle transitions and how
many individuals do so
successfully
 survivorship—fraction of
individuals that survive
from birth to different life
stages
 fecundity—average
number of offspring each
individual produces at
those life stages or ages
Survivorship curves
• What do lines I, II, and III say about the survivorship of each species?
I. Low mortality rate in early years
II. constant
mortality
throughout life
III. high mortality rate
early on in life
Characteristics of Three Types of Survivorship Curves:



Type I : Low mortality rate in early years.
 Small clutch sizes and good care for young…
humans, large mammals
Type II: constant mortality rate throughout
life…many animals
Type III: high mortality rate early in life
 large clutch size, little care for young…fish,
marine invertebrates
43.3 Life Histories Determine Population Growth Rates


Principle of allocation—once an organism has acquired a
unit of some resource, it can be used for only one function
at a time: maintenance, foraging, growth, defense, OR
reproduction
 In stressful conditions, more resources go to maintaining
homeostasis
Life-history tradeoffs—negative relationships among
growth, reproduction, and survival
 Ex: investments in reproduction may be at the expense
of survivorship or growth; age at first reproduction is
younger in large clutch size reproducers because they
invest less energy in their own growth and development.
Principle of Allocation
Figure 43.4 Resource Acquisition Increases with Resource Availability
Figure 43.4
Environmental
conditions
affect per
capita growth
rates (r) and
species
distributions
43.2 Births Increase and Deaths Decrease Population Size

Growth rate is dependent on birth rate and death rate (BD
model)
 N = population size
 B = number of births
t 1
t
 D = number of deaths
N
or
N=B–D
 N BD
43.2 Births Increase and Deaths Decrease Population Size

Birth rate (b = B/N)

Can be estimated for large populations by keeping track
of a sample of individuals called a cohort
Death rate (d = D/N)


Per capita growth rate (r) = average individual’s
contribution to total population growth rate
 r = b – d or
 dN/dt = rN

dN/dt is the change in population size per unit time (∆N/∆t)
43.4 Populations Grow Multiplicatively, but Not for Long


Exponential
(Multiplicative) growth
— an ever-larger number
of individuals is added in
each successive time
period (dN/dt = rmaxN)
Additive growth — a
constant number (rather
than a constant multiple)
is added in each time
period
Which line is which?
Exponential
growth
Additive
growth
(9/28) BR
4.
Populations never continue
to grow indefinitely. If
bacteria were able to
reproduce uninhibited
every 20 minutes, 1
bacterium would become
4,720,000,000,000,000,
000,000 in 24 hours. In
36 hours, the surface of
the earth would be buried
in a foot of bacteria. Why
doesn’t this happen?
43.4 Populations Grow Multiplicatively, but Not for Long

More individuals are produced than can possibly survive so
there is a struggle for existence that drives natural
selection and adaptations
“Every organic being naturally increases at so high a rate,
that, if not destroyed, the earth would soon be covered by the
progeny of a single pair…As more individuals are produced
than can possibly survive, there must in every case be a
struggle for existence.”
-Charles Darwin
Yellow star-thistle is a spiny annual plant native to the Mediterranean region. The
species is a noxious weed that has invaded several regions of the U.S. It is
unpalatable to bison. Rancher Jane discovers that 1 ha of her 128-ha pasture has
been invaded by star-thistle. A year later the population has grown to cover 2 ha.


How many hectares (ha) do you predict the star-thistle
population will cover in 1, 2, and 3 more years if the
population is growing additively? How many hectares if the
population is growing multiplicatively?
 Additively: 3, 4, 5; Exponentially: 4, 8, 16
Imagine that Rancher Jane only discovers the star-thistle
population after it has already covered 32 hectares of her
pasture. How many years does she have until the weed
completely covers the pasture if its population is growing
additively? Multiplicatively?
 Additively: 96 years; Exponentially: 2 years
43.4 Populations Grow Multiplicatively, but Not for Long

Exponential growth is
temporary


r is density dependent decreases as the population
becomes more crowded
Logistic growth – growth
slows as r nears 0;
population size stops
increasing when it reaches
its carrying capacity (K);
rmaxN((K-N)/K)
Which line is which?
Exponential
growth
Logistic growth
Examples of Logistic growth:
K-selected species - likely to be living at carrying capacity,
seen in areas with competition
Effect of Population Density on Per Capita Growth Rate
Effect of Population Density on Per Capita Growth Rate
When
population is
small, r is at its
maximum (rmax)
When population
density is below
K, r is positive
At carrying
capacity, r = 0
If population
exceeds K, r
becomes negative
and population
decreases
Exit: Population Practice Problem
1.
2.
3.
4.
5.
B = 34 , N = 1000
 Find b and apply that birth rate to a population of 500 to calculate the
number of births.
D = 16 , N = 1000
 Find d and apply that death rate to a population of 500 to calculate
the number of deaths.
Calculate r. Is this population increasing or decreasing?
How many individuals are added to the population of 500 in one year?
dN/dt = rN; for this example dN/dt = ? (assume dt = 1 year)
What is the population size after 1 year (starting size was 500)?
1.
2.
3.
4.
5.
Answer: b = 34/1000 = .034, so B = bN ; (.034)(500) = 17
Answer: D = dN ; (.016)(500) = 8
r = b – d ; .034 - .016 = .018; r is positive, so increasing (slowly)
Answer: .018(500) = dN/dt = 9 (could also use dN/dt = B – D)
500+ 9 = 509
(9/29) GROUP BR: Work in groups of 3-4!
1.
2.
3.
4.
How has the human population typically changed throughout history?
Has the growth rate changed in recent years? decades? centuries?
Have we experienced logistic or exponential growth? Both? Neither?
How much do you think the world population will change over the
course of this class? (http://www.breathingearth.net)
Starting population : 7,395,505,000
Limiting factors slow population growth. Some only limit growth when
populations reach a certain density. List some examples of these
density-dependent limiting factors.
Other limiting factors limit growth regardless of population density.
List some examples of these density-independent limiting factors.
43.4 Populations Grow Multiplicatively, but Not for Long




Spatial variation in resource availability can result in
variation of carrying capacity
Temporal variation in environmental conditions may cause
the population to fluctuate above and below the current
carrying capacity
Density-dependent limiting factors include competition
for resources, predation, and disease
Density-independent limiting factors include natural
disasters and human activities
43.4 Populations Grow Multiplicatively, but Not for Long

Human population has been growing exponentially
43.4 Populations Grow Multiplicatively, but Not for Long

Some believe we have
exceeded K due to:
 Dependency on fossil
fuels
 Climate change and
ecological degradation
Ecological Footprint
43.5 Extinction and Recolonization Affect Population Dynamics

Small subpopulations within a larger population are
vulnerable to environmental disturbances and chance
events are at greater risk of extinction
 Immigration (I) and emigration (E) may also impact
populations
Nt 1  Nt  B  I  D  E
43.6 Ecology Provides Tools for Managing Populations

Life histories can be useful in managing other spp
 Fisheries
 Ex: rockfish (exhibit indeterminate growth, and larger,
older females produce more eggs)
 Reducing disease risk
 Ex: ticks
 Conservation of endangered species
 Extinction prevention
 Continuous corridors of habitat can connect
subpopulations and allow dispersal/migration (article)
Habitat Corridors connect fragmented habitats
EXIT
World Population at start of class: 7,395,505,000
World Population at end of class: : 7,395,51
Population at end of class LAST YEAR: 7,320,072,720
Population on October 31st, 2013: 7,000,000,000
3. What is the
carrying capacity
of this population?
What is the growth
rate (r)?
4. How much will the
population increase
in one generation
(dn/dt) if the
starting population
is 800 individuals?
What about if the
starting population
is 1100? Show your
work!
Population pyramids are used to estimate how a population
will change in the future
1. Identify the populations in the age-structure diagrams below as either
expanding, stable, or contracting.
2. How did you think the “bulge” will affect population growth in the U.S.?
Exit: Reflection
Create 2 rectangles on your bellringer, and label one “Clear” and
the other “Unclear.” In the “Clear” box, write down the information
from CH 42 that you feel you understand. In the “Unclear” box,
write down any information or concepts about which you feel
confused.