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Ecology
• Study of how organisms interact with each
other and with their environment
Levels of Ecological Organization
• Populations
– groups of individuals of the same species living
together in one area
• Communities
– populations of different species living together
in one area
• Ecosystems
– communities and the non-living parts of the
environment with which they interact
Population Structure
Key aspects:
• Population Size
• Population Density
• Population Dispersion
Population Size
• Affects populations ability to survive
• small populations - more likely to go extinct
Population Density
• Number of individuals per unit area
• low density can be problem too
Population Dispersion
• Spacing of individuals within the population
• Random, uniform or clumped
• Clumped dispersion is when individuals
aggregate in patches.
Fig. 52.2a
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• By contrast, uniform dispersion is when
individuals are evenly spaced.
Fig. 52.2b
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• In random dispersion, the position of each
individual is independent of the others.
• Overall, dispersion depends on resource
distribution.
Fig. 52.2c
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Survivorship Curves
• Graphical representation of the survivorship
(opposite of mortality) at each age
Survivorship Curves
• Type I
– increased risk of dying when old
• Type II
– equal chance of dying at all ages
• Type III
– increased chance of dying when young
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1.0
Fig. 56.10
Human (type I)
Proportion Surviving
Hydra (type II)
0.1
0.01
Oyster (type III)
0.001
0
25
50
75
Percent of Maximum Life Span
100
Proportion Surviving
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Fig. 56.11
1.0
0.5
0.4
0.3
0.2
0.1
0.05
0.04
0.03
0.02
0.01
0.005
0.004
0.003
0.002
3
6
9
12
15
18
21
24
Age (months)
Poa annua – most like
Type II
27
Population Growth
• Biotic Potential
–r
– the rate a population would grow at with no
limits
– intrinsic rate of increase
Exponential Growth
dN/dt = rN
r = (b - d) + (i - e)
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Fig.
56.16-1
dN
= 1.0 N
1250
dt
Population Size (N)
1000
750
500
250
0
0
5
10
Number of Generations (t)
15
Carrying Capacity
• populations eventually reach a limit to their
growth
• K = number of individuals that the
environment can support
Logistic Growth
dN/dt = rN ((K - N)/ K)
• growth rate slows as the carry capacity is
approached
• sigmoid growth curve (S-shaped)
• most populations remain constant in size
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Fig.
56.16
dN
= 1.0 N
1250
dt
Carrying
capacity
Population Size (N)
1000
750
dN = 1.0 N
dt
500
1000 – N
1000
250
0
0
5
10
Number of Generations (t)
15
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Population Growth Rate (dN/dt)
Fig. 56.17
Positive
Growth
Rate
N=K
0
Negative
Growth
Rate
Below K
Carrying
Capacity (K)
Population Size (N)
Above K
Fig. 56.18
Logistic Growth
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Number of Breeding Male
Fur Seals (thousands)
10
8
6
4
2
0
1915
a.
1925
1935
Time (years)
1945
Number of Cladocerans (per 200 mL)
500
b.
400
300
200
100
0
0
10
20
30
40
Time (days)
50
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6
Fig. 56.24
Billions of People
5
4
Significant advances
in public health
3
2
Industrial
Revolution
1
Bubonic plague
“Black Death”
4000
B.C.
3000
B.C.
2000
1000
B.C.
B.C.
Year
0
1000
2000
Limits to Population Growth
• Resource limitation- competition
• predation
Community Ecology
• Study interactions among populations
• Niche
– total of all the ways an organism uses resources
in its environment
– food consumption, space utilization, temp
range, etc...
• Habitat
– physical location
Competition
• struggle between organisms to utilize the
same resource when the resource is limited
• niches overlap and resources are limited
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Fig. 57.4
Chthamalus
Chthamalus
realized niche
Chthamalus
fundamental
niche
High tide
Semibalanus
Low tide
Semibalanus
realized niche
Semibalanus
fundamental
niche
S.balanoides and C.stellatus competing
C.stellatus fundamental and
realized niches are identical when
S.balanoides is removed.
J.H. Connell’s classical study of barnacles
Competition
• “fighting” = interference competition
• consuming shared resources = exploitative
competition
Competition
• Interspecific competition
– between individuals from different species
• Intraspecific competition
– between individuals from same species
One Possible
Result of Competition
• Competitive exclusion
– no species can occupy the same niche
indefinitely
– one species will be outcompeted and be driven
to extinction locally
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Population Density
(measured by volume)
200
Fig. 57.5
Gausse’s
Experiments
150
100
50
0
0
4
8
12
Days
16 20
24
0
4
8
12 16
Days
20
24
0
4
8
12
16
20
24
Days
a.
Paramecium caudatum
Paramecium aurelia
Paramecium bursaria
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Paramecium caudatum
Paramecium aurelia
Paramecium bursaria
Population Density
(measured by volume)
200
150
100
50
0
0
4
8
12
16
20
24
Days
b.
Competitive Exclusion
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Paramecium caudatum
Paramecium aurelia
Paramecium bursaria
Population Density
(measured by volume)
75
50
25
0
0
4
8
12 16 20 24
Days
c.
Coexistence…Resource Partitioning
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Population Density
(measured by volume)
200
Fig. 57.5
150
100
50
0
0
4
8
12
16
20
24
0
4
8
12 16
Days
20
24
0
4
Days
8
12
16
20
24
Days
a.
Paramecium caudatum
Paramecium aurelia
Paramecium bursaria
Population Density
(measured by volume)
Population Density
(measured by volume)
200
150
100
50
50
25
0
0
0
4
8
12 16
20
24
0
Days
b.
75
4
8
12
Days
c.
16
20
24
Other Results of Competition
• Niche overlap can lead to...
– Resource partitioning
– character displacement
– Resource partitioning is the differentiation
of niches that enables two similar species to
coexist in a community.
Fig. 53.3
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 53.2
• Character displacement is the tendency for
characteristics to be more divergent in sympatric
populations of two
species than in
allopatric
populations
of the same two
species.
– Hereditary changes
evolve that bring
about resource
partitioning.
Fig. 53.4
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Predation
• Predator uses prey for food
• prey evolves defenses, predator evolves
adaptations to overcome…arms race
Predation
Plant defenses against herbivores:
• morphological - thorns, spines, plant hairs
• chemicals - secondary compounds
Predation
Animal defenses against predators:
• Behavioral defenses include fleeing,
hiding, self-defense, noises, and mobbing.
• Camouflage includes cryptic coloration,
Leaf mimic katydid from the
Ecuadorian Amazon
• Deceptive Markings: eyespots
http://www.flickr.com/photos/la
dyoftheflowers/2386058994/
http://discovermagazine.com/photos/11-the-calculating-beauty-of-butterflies
• Mechanical defenses include spines & shells.
african-safari-pictures.com
http://www.animalpictures1.com/r-sea-urchin-112-sea-urchin-1958.htm
• Chemical defenses include odors and toxins –
may get them from the plants they eat (ex:
monarch butterfly & milkweed)
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• Aposematic coloration is indicated by warning
colors, and is sometimes associated with other
defenses (toxins).
Fig. 53.6
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Mimicry is when organisms resemble other
species.
– Batesian mimicry is where a harmless species mimics
a harmful one.
Copyright © 2002 Pearson Education, Inc., publishing as
Benjamin Cummings
• Müllerian mimicry is where two or more
unpalatable species resemble each other.
Fig. 53.8
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Fig. 57.14
Battus philenor
Papilio glaucus
a. Batesian mimicry: Pipevine swallowtail butterfly (Battus philenor) is
poisonous; Tiger swallowtail (Papilio glaucus) is a palatable mimic.
Heliconius erato
Heliconius sapho
Heliconius melpomene
Heliconius cydno
b. Müllerian mimicry: Two pairs of mimics; all are distasteful.
Predation
• Can promote species diversity
• predator eats superior competitor
• Keystone species
exert an important
regulating effect
on other species
in a community.
Fig. 53.14
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• If they are removed, community structure is greatly
affected.
Fig. 53.15
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Coevolution & interspecific interactions
– Coevolution refers to reciprocal evolutionary
adaptations of two interacting species.
• When one species evolves, it exerts selective
pressure on the other to evolve to continue the
interaction.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
The Oogpister Beetle Video
http://www.snotr.com/video/4732