Lec79%20pop%20ecology10am

Lec79%20pop%20ecology10am - 4/24/09


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Unformatted text preview: 4/24/09
 Lecture
79:
Population
ecology
 USA
Population
dynamics
in
50
 minutes
 •  http://www.breathingearth.net/
 Fig. 52-2 Organismal
 ecology
 Population
 ecology
 Community
 ecology
 •  A
population
is
a
group
of
individuals
of
the
same
 species
living
in
an
area
 •  Population
ecology
focuses
on
factors
affecting
 how
many
individuals
of
a
species
live
in
an
area
 Ecosystem
 ecology
 Landscape
 ecology
 Global
 ecology
 Metapopulations
 •  Metapopulations
are
groups
of
populations
linked
by
 immigration
and
emigration
 •  High
levels
of
immigration
combined
with
higher
survival
can
 result
in
greater
stability
in
populations
 ˚
 Aland
 Islands
 EUROPE
 Saskya
van
Nouhuys
 5
km
 Occupied
patch
 Unoccupied
patch
 1
 4/24/09
 Population
Dynamics
 •  The
study
of
population
dynamics
focuses
on
the
 complex
interactions
between
biotic
and
abiotic
 factors
that
cause
variation
in
population
size
 Important
terms…
 •  Dispersion
is
the
pattern
of
spacing
among
individuals
 within
the
boundaries
of
the
population
 •  Density
is
the
number
of
individuals
per
unit
area
or
 volume
 •  Abundance
is
the
relative
representation
of
a
species
 in
a
particular
ecosystem.
It
is
usually
measured
as
the
 number
of
individuals
found
per
sample.
How
species
 abundances
are
distributed
within
an
ecosystem
is
 referred
to
as
relative
species
abundances.
 Fig.
53‐3
 Births
 Deaths
 In
a
clumped
dispersion,
individuals
aggregate
 in
patches
 A
clumped
dispersion
may
be
influenced
by
 resource
availability
and
behavior
 (a)
Clumped
 Births
and
immigration
 add
individuals
to
 a
population.
 Deaths
and
emigration
 remove
individuals
 from
a
population.
 (b)
Uniform
 A
uniform
dispersion
is
one
in
which
individuals
 are
evenly
distributed
 It
may
be
influenced
by
social
interactions
such
 as
territoriality
 Immigration
 Emigration
 (c)
Random
 In
a
random
dispersion,
the
position
of
each
 individual
is
independent
of
other
individuals
 Territorial
dance
–
maintaining
 uniformal
distribution
 • 
The
knowledge
of
population
distribution
is






 essential
for
statistical
analysis
 What
is
the
height
of
this
class?
 • Lots
of
different
heights
 • Large
variance

 mean
 2
 4/24/09
 Statistical
predictions…
 • 
Predicting
the
height
of
all
biology
students
 •  Using
a
SAMPLE
to
 make
predictions
for
a
 POPULATION
 –  Sample:
our
class
 –  Population:
all
biology
 students
in
the
Cornell
 biology
program
 Often
a
population
is
way
too
large
to
observe
every
 single
individual

 •  WHY?….
 Sampling
 Population
size
estimation
 •  Population
size
can
be
estimated
by
mark‐ recapture
method
 recaptured
marked
individuals
/
captured
individuals
 marked
and
released
individuals
/

population
size
 Population
size
estimation
 •  Population
size
can
be
estimated
by
extrapolation
 from
small
samples
 Life
Tables
 •  A
life
table
is
an
age‐specific
summary
of
the
 survival
pattern
of
a
population
 •  It
is
best
made
by
following
the
fate
of
a
cohort,
a
 group
of
individuals
of
the
same
age
 3
 4/24/09
 Survivorship
Curves
 •  A
survivorship
curve
is
a
graphicway
of
 representing
the
data
in
a
life
table
 1,000
 Number
of
survivors
(log
scale)
 Survivorship
curves
can
be
 classified
into
three
general
 types:
 Type
I
 Type
II
 Type
III
 100
 Females
 10
 Males
 –  Type
I:
low
death
rates
during
early
and
middle
life,
 then
an
increase
among
older
age
groups
 –  Type
II:
the
death
rate
is
constant
over
the
 organism’s
life
span
 –  Type
III:
high
death
rates
for
the
young,
then
a
 slower
death
rate
for
survivors
 0
 1
 2
 4
 6
 Age
(years)
 8
 10
 Fig.
53‐6
 Which
survivorship
curve(s)
represent(s)
humans?
 Number
of
survivors
(log
scale)
 Type
I:
low
death
rates
during
early
and
 middle
life,
then
an
increase
among
older
 age
groups
 1,000
 I
 A,
Type
III
 B,
Type
II
 C,
Type
I
 D,
Both
Type
I
and
II
 E,
Both
Type
II
and
III
 C
 B
 100
 II
 10
 III
 1
 0
 50
 Percentage
of
maximum
life
span
 100
 A
 Reproductive
Rates
 •  A
reproductive
table,
or
 fertility
schedule,
is
an
 age‐specific
summary
of
 the
reproductive
rates
in
 a
population
 •  It
describes
reproductive
 patterns
of
a
population
 Natural
selection

Life
History
 Trade‐off
 4
 4/24/09
 Natural
selection

Life
History
 •  An
organism’s
life
history
comprises
the
traits
that
 affect
its
schedule
of
reproduction
and
survival:
 –  The
age
at
which
reproduction
begins
 –  How
often
the
organism
reproduces
 –  How
many
offspring
are
produced
during
each
 reproductive
cycle
 •  Species
that
exhibit
 semelparity,
or
big‐bang
 reproduction,
reproduce
 once
and
die
 •  Highly
variable
or
 unpredictable
 environments
 Species
that
exhibit
 iteroparity,
or
repeated
 reproduction,
produce
 offspring
repeatedly
 Dependable
environments
 • 

Survival
rate
of
the
offspring
 • 

Likelihood
that
the
adult
will
survive
and
reproduce
again
 Per
capita
(individual)
rate
of
increase
 During
time
interval
Δt
population
size
changes
ΔN
 Increases
population
size
 decreases
population
size
 Per
capita
(individual)
rate
of
increase
 •  •  •  •  •  If
Δt=
1
year
 
N=
1000
female
wasps
 B=
500
offspring
 b=
500/1000=0.5
(annual
per
capita
birth
rate)
 B=bN
 Expected
number
of
births
per
year
of
a
 population
of
5000
wasps
=
0.5*5000=2500
 number
of
offspring
produced
/
number
of
individuals
in
population

 Per
capita
death
rate
is
calculated
similarly=
d
 •  •  •  •  •  r=
per
capita
rate
of
increase
 r=
b
–
d
 r
<
0

declining
population
 r
>
0
growing
population
 r=
0
Zero
population
growth
 ΔN
 =
 rN
 Δt
 where
N
=
population
size,
t
=
time,

 and
r
=
per
capita
rate
of
increase
=
birth
–
death

 …a
little
US
History……
 • In
September
1969
U.S.
Senator
Nelson
of
Wisconsin
 announced
that
in
spring
1970
there
would
be
a
nationwide
 grassroots
demonstration
on
the
environment.

 • This
occurred
during
a
time
of
great
concern
about
 overpopulation
and
when
there
was
a
strong
movement
 towards
"Zero
Population
Growth.”
 • April
22,
1970.
This
day
marks
the
beginning
of
the
modern
 environmental
movement.
Approximately
20
million
 Americans
participated,
with
a
goal
of
a
healthy,
sustainable
 environment.
 5
 4/24/09
 What
was
first
celebrated
on
April
22,
 1970,
and
what
do
we
celebrate
 today?

 A.  Rachel
Carson’s
birthday
 B.  Sustainability
day
 C.  Earth
Day
 D.  Arbor
Day
 E.  The
end
of
the
Vietnam
War
 What
was
first
celebrated
on
April
22,
 1970,
and
what
do
we
celebrate
 today?

 A.  Rachel
Carson’s
birthday
 B.  Sustainability
day
 *
C.  Earth
Day
 D.  Arbor
Day
 E.  The
end
of
the
Vietnam
War
 Vs.
 Ecology
flag
of
Earth
Day
 •  Senator
Nelson
chose
the
date
as
the
one
that
could
maximize
 participation
on
college
campuses
for
what
he
conceived
as
 an
environmental
teach‐in.

 •  He
determined
that
the
week
of
April
19‐25
was
the
best
bet.
 It
did
not
fall
during
exams
or
spring
breaks,
did
not
conflict
 with
religious
holidays
and
was
late
enough
in
spring
to
have
 decent
weather.
 •  Asked
whether
he
had
purposely
chosen
Lenin's
100th
 birthday,
Nelson
explained
that
with
only
365
days
a
year
and
 3.7
billion
people
in
the
world,
every
day
was
the
birthday
of
 ten
million
living
people.
 • According
to
Flags
of
the
World,
the
Ecology
Flag
was
 published
for
the
first
time
in
October
25,
1969.
 • 
The
flag
was
patterned
after
the
flag
of
the
United
 States,
and
had
thirteen
stripes
alternating
green
and
 white.
Its
canton
was
green
with
a
yellow
theta.

 • Flags
used
either
a
theta
because
of
its
historic
use
as
a
 warning
symbol,
or
the
peace
symbol.
Theta
would
later
 become
associated
with
Earth
Day.
 Exponential
Growth
 •  Exponential
population
 growth
is
population
 increase
under
idealized
 conditions
 •  Under
these
conditions,
the
 rate
of
reproduction
is
at
its
 maximum,
called
the
 intrinsic
rate
of
increase
 K=carrying
capacity
 •  is
the
maximum
population
size
the
environment
 can
support
 dN
 =
 r N
 dt
 max 6
 4/24/09
 The
Logistic
Growth
Model
 •  In
the
logistic
population
growth
model,
the
per
capita
 rate
of
increase
declines
as
carrying
capacity
is
reached
 •  We
construct
the
logistic
model
by
starting
with
the
 exponential
model
and
adding
an
expression
that
 reduces
per
capita
rate
of
increase
as
N
approaches
K
 Number
of
additional
 Individuals
the
habitat
 can
support
 The
Logistic
Growth
Model
 (K
‐
N)
 dN
 =
 dt
 rmax
N
 K
 If
N<K
the
rate
of
increase
is
close
to
maximum
 If
N=K
the
population
stops
growing

 Birth
or
death
rate
 per
capita
 •  Some
populations
show
an
Allee
effect,
in
which
 individuals
have
a
more
difficult
time
surviving
or
 reproducing
if
the
population
size
is
too
small
 Fig.
53‐15
 Density‐dependent
 birth
rate
 Density‐
 dependent
 death
rate
 Equilibrium
 density
 Population
density
 (a)
Both
birth
rate
and
death
rate
vary.
 Density‐dependent
 death
rate
 Density‐dependent
 birth
rate
 Density‐
 independent
 death
rate
 Equilibrium
 density
 Population
density
 (b)
Birth
rate
varies;
death
rate
is
constant.
 Birth
or
death
rate
 per
capita
 Density‐
 independent
 birth
rate
 Equilibrium
 density
 Population
density
 •  In
density‐independent
 populations,
birth
rate
and
 death
rate
do
not
change
 with
population
density
 •  In
density‐dependent
 populations,
birth
rates
fall
 and
death
rates
rise
with
 population
density
 (c)
Death
rate
varies;
birth
rate
is
constant.
 The
Logistic
Model
and
Life
Histories
 •  Life
history
traits
favored
by
natural
selection
may
 vary
with
population
density
and
environmental
 conditions
 dN
 (K
‐
N)
 dt
 =
 rmax
 N
 K
 K‐selection,
or
density‐dependent
 selection,
 selects
for
life
history
traits
that
are
 sensitive
to
population
density
 N
=
K
 Competition
for
resources
is
strong
 r‐selection,
or
density‐independent
 selection,

 selects
for
life
history
traits
that
 maximize
reproduction
 N<<<K
 Uncrowded
environment
 Density
dependent
regulators
 –  What
environmental
factors
stop
a
population
from
growing
 indefinitely?
 –  Why
do
some
populations
show
radical
fluctuations
in
size
 over
time,
while
others
remain
stable?
 Negative
feedback
that
regulates
population
growth
 •  competition
for
resources
 •  territoriality

 •  disease
 •  predation
 •  toxic
wastes
 •  intrinsic
factors
 7
 4/24/09
 Competition
for
Resources
 •  In
crowded
populations,
increasing
population
 density
intensifies
competition
for
resources
and
 results
in
a
lower
birth
rate
 Territoriality
 Disease
 •  In
dense
populations,
pathogens
and
parasites
can
 spread
more
rapidly
 Predation
 •  As
a
prey
population
builds
up,
predators
may
feed
 preferentially
on
that
species
 "Everything—birds,
rodents,
small
mammals,
 even
snakes,
lizards,
and
fish
will
feed
heavily
 on
cicadas
when
they
are
out,”
‐‐Keith
Clay,
 Indiana
University.
 Intrinsic
(physiological)
Factors
 Population
Dynamics
 •  interactions
between
biotic
and
abiotic
factors
that
 cause
variation
in
population
size
 Abiotic
‐‐
weather
 Biotic
‐‐
predation
 8
 4/24/09
 Population
dynamics
 Population
dynamics
 Population
Dynamics
 •  Lynx
populations
follow
the
10
year
boom‐and‐bust
 cycle
of
hare
populations

 The
Lynx
and
the
Hare…..
 •  Hypothesis
1:
The
hare’s
 population
cycle
follows
a
 cycle
of
winter
food
supply
 •  Hypothesis
2:
The
hare’s
 population
cycle
is
driven
by
 pressure
from
other
 predators
 •  Hypothesis
3:
The
hare’s
 population
cycle
is
linked
to
 sunspot
cycles
 Delayed
response
of
the
predator
 Food
supply
hypothesis
 •  If
this
hypothesis
is
correct,
then
the
cycles
should
 stop
if
the
food
supply
is
increased
 •  Additional
food
was
provided
experimentally
to
a
 hare
population,
and
the
whole
population
 increased
in
size
but
continued
to
cycle
 •  No
hares
appeared
to
have
died
of
starvation
 Predator
hypothesis
 •  In
a
study
conducted
by
field
ecologists,
90%
of
the
 hares
were
killed
by
predators
 •  These
data
support
this
second
hypothesis
 9
 4/24/09
 Sunspot
hypothesis
 •  Sunspot
activity
affects
light
quality,
which
in
turn
 affects
the
quality
of
the
hares’
food
 •  There
is
good
correlation
between
sunspot
activity
 and
hare
population
size
 A
sunspot
is
a
region
on
the
Sun's
surface
 (photosphere)
that
is
marked
by
intense
 magnetic
activity,
which
inhibits
convection,
 forming
areas
of
reduced
surface
 temperature.
The
contrast
with
the
 surrounding
material
at
about
5,800
K
leaves
 them
clearly
visible
as
dark
spots.
 “….the
sunspot
activity
is
as
good
or
partly
a
better
 explanation
for
the
general
warming
trend
in
climate
 than
the
amount
of
greenhouse
gases.
….”
‐‐‐
Timo
 Niroma,
Helsinki,
Finland
 Population
dynamics
 •  The
results
of
all
these
experiments
suggest
that
 both
predation
and
sunspot
activity
regulate
hare
 numbers
and
that
food
availability
plays
a
less
 important
role
 The
human
population
dynamics
 The
human
population
dynamics
 •  No
population
can
grow
indefinitely,
and
humans
 are
no
exception
 •  No
population
can
grow
indefinitely,
and
humans
 are
no
exception
 •  Though
the
global
population
is
still
growing,
the
 rate
of
growth
began
to
slow
during
the
1960s
 Regional
Patterns
of
Population
Change
 •  To
maintain
population
stability,
a
regional
human
 population
can
exist
in
one
of
two
configurations:
 –  Zero
population
growth
=

 High
birth
rate
–
High
death
rate
 –  Zero
population
growth
=
 Low
birth
rate
–
Low
death
rate
 •  The
demographic
transition
is
the
move
from
the
 first
state
toward
the
second
state
 10
 4/24/09
 •  The
demographic
transition
is
associated
with
an
 increase
in
the
quality
of
health
care
and
improved
 access
to
education
 Natural
selection

Life
History
 Trade‐off
 Age
Structure
 •  One
important
demographic
factor
in
present
and
 future
growth
trends
is
a
country’s
age
structure
 •  Age
structure
is
the
relative
number
of
individuals
 at
each
age
 Infant
Mortality
and
Life
Expectancy
 •  Infant
mortality
and
life
expectancy
at
birth
vary
 greatly
among
developed
and
developing
countries
 but
do
not
capture
the
wide
range
of
the
human
 condition
 Global
Carrying
Capacity
 •  How
many
humans
can
the
biosphere
support?
 Global
Carrying
Capacity
 The
ecological
footprint
concept
summarizes
the
 aggregate
land
and
water
area
needed
to
sustain
the
 people
of
a
nation
 Use
of
photosynthetic
products
 Sustainable:
Productive
land/population
size=
2
ha/person
 USA:
10
ha
ecological
footprint
per
capita
 11
 4/24/09
 Global
Carrying
Capacity
 



Nonrenewable
 resources

 Meat
consumption
 Universal
carrying
capacity
 Water
 Waste
 The
Great
Pacific
Garbage
Patch,
also
 described
as
the
Eastern
Garbage
 Patch
or
the
Pacific
Trash
Vortex,
is
a
 gyre
of
marine
debris
in
the
central
 North
Pacific
Ocean
located
roughly
 between
135°
to
155°W
and
35°
to
 42°N.

 Earth
dynamics
 •  http://www.breathingearth.net/
 dN
 =
 r N
 dt
 max 12
 ...
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This note was uploaded on 10/20/2009 for the course BIO G 1102 taught by Professor Walcott during the Spring '08 term at Cornell.

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