ch. 53 introduction to ecology and the...
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AP Biology
Ch. 53
Introduction to Ecology
and the Biosphere
population
ecosystem
community
biosphere
organism
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Life takes place in populations
Population
group of individuals of same species in
same area at same time rely on same
resources
interact
interbreed
Population Ecology: What factors affect a population?
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Why Population Ecology? Scientific goal
understanding the factors that influence the size of populations general principles
specific cases
Practical goal
management of
populations increase population size
endangered species
decrease population size
pests
maintain population size
fisheries management
maintain & maximize sustained yield
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Density: A Dynamic Perspective
In most cases, it is impractical or impossible to
count all individuals in a population
Sampling techniques can be used to estimate
densities and total population sizes
• Population size can be estimated by either
Extrapolation from small samples
Index of population size (e.g., number of
nests)
Mark-recapture method
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Mark-recapture method
Scientists capture, tag, and release a random
sample of individuals (s) in a population
Marked individuals are given time to mix back
into the population
Scientists capture a second sample of
individuals (n), and note how many of them are
marked (x)
Population size (N) is estimated by
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sn
x N
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Abiotic factors
sunlight & temperature
precipitation / water
soil / nutrients
Biotic factors
other living organisms
prey (food)
competitors
predators, parasites,
disease
Intrinsic factors
adaptations
Factors that affect Population Size
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Characterizing a Population
Describing a population
population range
pattern of spacing
density
size of population
1937
1943 1951
1958 1961
1960 1965 1964
1966 1970
1970
1956
Immigration from Africa
~1900
Equator
range
density
Hey, I was
captured
last week and
got marked.
Ha ha! That has a
RFID tag Imbedded.
Expect to be
abducted and
measured periodically
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Population Range
Geographical limitations
abiotic & biotic factors temperature, rainfall, food, predators, etc.
habitat
adaptations to polar biome
adaptations to
rainforest biome
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Changes in range
Range expansions & contractions
changing environment
Woodlands
Grassland, chaparral, and desert scrub
15,000 years ago-glacial period
Alpine tundra
Spruce-fir forests
Mixed conifer forest
0 km
2 km
3 km
1 km Ele
vati
on
(km
)
Present Alpine tundra
Spruce-fir forests
Mixed conifer forest
Woodlands
Grassland, chaparral, and
desert scrub
aspen oak, maple white birch sequoia
result of competition
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Density is the result of an interplay between
processes that add individuals to a population and
those that remove individuals
Immigration- influx of new individuals from other
areas
Emigration - movement of individuals out of a
population
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Births Deaths
Immigration
Emigration
Births and immigration add individuals to
a population. Deaths and emigration
remove individuals from a population.
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At risk populations
Endangered species
limitations to range / habitat
places species at risk
Socorro isopod
Devil’s hole pupfish
Iriomote cat
Northern white rhinoceros
New Guinea tree kangaroo
Iiwi Hawaiian
bird
Catalina Island
mahogany tree
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Population Spacing
Dispersal patterns within a population
uniform
random
clumped
Provides insight into the
environmental associations
& social interactions of
individuals in population
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Clumped Pattern (most common)
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Uniform
Clumped patterns
May result from
direct interactions
between individuals
in the population
territoriality
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Random • The position of each individual is independent
of other individuals
• It occurs in the absence of strong attractions
or repulsions
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Population Size
Changes to
population size
adding & removing
individuals from a
population
birth
death
immigration
emigration
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Population growth rates
Factors affecting population growth rate
sex ratio
how many females vs. males?
generation time
at what age do females reproduce?
age structure
how females at reproductive age in cohort?
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Life table
Demography
Factors that affect growth & decline of
populations
vital statistics & how they change over time
Why do teenage boys pay high car insurance rates?
females males
What adaptations have led to this difference
in male vs. female mortality?
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Survivorship curves Graphic representation of life table
Belding ground squirrel
The relatively straight lines of the plots indicate relatively constant
rates of death; however, males have a lower survival rate overall
than females.
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Age structure
Relative number of individuals of each age What do these data imply about population growth in these countries?
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Survivorship curves
Generalized strategies
What do these graphs
tell about survival &
strategy of a species?
0 25
1000
100
Human (type I)
Hydra (type II)
Oyster (type III)
10
1
50
Percent of maximum life span
100 75
Su
rviv
al
pe
r th
ou
sa
nd
I. High death rate in
post-reproductive
years
II. Constant mortality
rate throughout life
span
III. Very high early
mortality but the
few survivors then
live long (stay
reproductive)
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Trade-offs: survival vs. reproduction
The cost of reproduction
increase reproduction may decrease
survival
age at first reproduction
investment per offspring
number of reproductive cycles per lifetime
Natural selection
favors a life
history that
maximizes lifetime
reproductive
success
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Parental survival
Kestrel Falcons:
The cost of larger
broods to both male
& female parents
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Reproductive strategies
K-selected
late reproduction
few offspring
invest a lot in raising offspring
primates
coconut
r-selected
early reproduction
many offspring
little parental care
insects
many plants
K-selected
r-selected
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Populations in which individuals have a more
difficult time surviving or reproducing if the
population size is too small
Allee effect
Smaller populations suffer ever
decreasing reproductive success.
The smaller the group size, the
poorer their output of offspring per
individual . . . which leads to even
smaller populations, which have
even poorer reproductive outlooks . .
. and the whole scenario makes the
fight to restore populations a
challenging uphill battle.
Passenger pigeon and
African Wild Dogs
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Trade offs
Number & size of offspring
vs.
Survival of offspring or parent r-selected
K-selected
“Of course, long before you mature,
most of you will be eaten.”
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Life strategies & survivorship curves
0 25
1000
100
Human (type I)
Hydra (type II)
Oyster (type III)
10
1
50
Percent of maximum life span
100 75
Su
rviv
al
pe
r th
ou
sa
nd
K-selection
r-selection
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Population growth
change in population = births – deaths
Exponential model (ideal conditions)
dN = riN dt
N = # of individuals
r = rate of growth
ri = intrinsic rate
t = time
d = rate of change
growth increasing at constant rate
intrinsic rate = maximum rate of growth
every pair has
4 offspring
every pair has
3 offspring
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African elephant
protected from hunting
Whooping crane
coming back from near extinction
Exponential growth rate Characteristic of populations without
limiting factors
introduced to a new environment or rebounding from a catastrophe
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Regulation of population size
Limiting factors
density dependent
competition: food, mates,
nesting sites
predators, parasites,
pathogens
density independent
abiotic factors
sunlight (energy)
temperature
rainfall
swarming locusts
marking territory
= competition
competition for nesting sites
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Stability and Fluctuation
Long-term population studies have challenged
the hypothesis that populations of large
mammals are relatively stable over time
Both weather and predator population can
affect population size over time
For example, the moose population on Isle
Royale collapsed during a harsh winter, and
when wolf numbers peaked
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Wolves Moose
Year
Nu
mb
er
of
wo
lves
Nu
mb
er
of
mo
ose
1955 1965 1975 1985 1995 2005
50
40
30
20
10
0
2,500
2,000
1,500
1,000
500
0
Figure 53.18
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Population Cycles: Scientific Inquiry
Some populations undergo regular boom-and-
bust cycles
Lynx populations follow the 10-year boom-and-
bust cycle of hare populations
Three hypotheses have been proposed to
explain the hare’s 10-year interval
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Snowshoe hare
Lynx
Year
1850 1875 1900 1925
Nu
mb
er
of
hare
s
(th
ou
san
ds)
Nu
mb
er
of
lyn
x
(th
ou
san
ds)
160
120
80
40
0
9
6
3
0
Figure 53.19
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Hypothesis: 1 The hare’s population cycle
follows a cycle of winter food supply
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
These data do not support the first hypothesis
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Hypothesis 2: The hare’s population cycle is
driven by pressure from other predators
In a study conducted by field ecologists, 90%
of the hares were killed by predators
These data support the second hypothesis
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Hypothesis 3: The hare’s population cycle is
linked to sunspot cycles
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
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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
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Introduced species
Non-native species
transplanted populations grow
exponentially in new area
out-compete native species
loss of natural controls
lack of predators, parasites,
competitors
reduce diversity
examples
African honeybee
gypsy moth
zebra mussel
purple loosestrife kudzu
gypsy moth
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Zebra mussel
ecological & economic damage
~2 months
reduces diversity
loss of food & nesting sites
for animals
economic damage
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Purple loosestrife
1968 1978
reduces diversity
loss of food & nesting sites
for animals
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K =
carrying
capacity
Logistic rate of growth
Can populations continue to grow
exponentially? Of course not!
effect of
natural controls
no natural controls
What happens as N approaches K?
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500
400
300
200
100
0 20 0 10 30 50 40 60
Time (days)
Nu
mb
er
of
cla
do
cera
ns
(p
er
20
0 m
l)
Maximum population size that environment can support with no degradation of habitat
varies with changes in resources
Time (years) 1915 1925 1935 1945
10
8
6
4
2
0
Nu
mb
er
of
bre
ed
ing
ma
le
fu
r s
ea
ls (
tho
us
an
ds
)
Carrying capacity
What’s going on with the plankton?
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Changes in Carrying Capacity
Population cycles
predator – prey
interactions
At what population level is the carrying capacity?
K
K
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Human population growth
What factors have contributed to this exponential growth pattern?
1650500 million
20056 billion
Industrial Revolution
Significant advances in medicine through science and technology
Bubonic plague "Black Death"
Population of… China: 1.3 billion India: 1.1 billion
adding 82 million/year
~ 200,000 per day! Doubling times
250m 500m = y ()
500m 1b = y ()
1b 2b = 80y (1850–1930)
2b 4b = 75y (1930–1975)
Is the human population reaching carrying capacity?
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Distribution of population growth
1
2
3
Time 1950 1900 2000
Developing countries
2050
4
5
6
7
8
9
10
11
0
Developed countries
Wo
rld
po
pu
lati
on
in
billio
ns
World total
uneven distribution of population:
90% of births are in developing countries
uneven distribution of resources:
wealthiest 20% consumes ~90% of resources
increasing gap between rich & poor
What is K for humans? 10-15 billion?
There are choices as
to which future path
the world takes…
the effect of income
& education
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Ecological Footprint 30.2
15.6
6.4
3.7
3.2
2.6
USA
Germany
Brazil
Indonesia
Nigeria
India
Amount of land required to support an individual at standard of living of population
2 0 4 6 8 12 10 14 16 18 20 22 24 26 28 30 32 34
Acres
uneven distribution:
wealthiest 20% of world:
86% consumption of resources
53% of CO2 emissions
over-population or over-consumption?
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Ecological Footprint
Based on land & water area used to produce all resources each country consumes & to absorb all wastes it generates
deficit surplus
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Any
Questions?
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Difficult to count a moving target
Measuring population density
How do we measure how many
individuals in a population?
number of individuals in an area
mark & recapture methods
sampling populations
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Evolutionary adaptations
Coping with environmental variation
regulators
endotherms
homeostasis
(“warm-blooded”)
conformers
ectotherms
(“cold-blooded”)
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Bright blue marble spinning in space
Ecology
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biosphere
ecosystem
community
population
Studying organisms in their environment
organism