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Community Ecology,
Population Ecology, and
Sustainability
Chapter 6
Why Should We Care about the
American Alligator?
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Overhunted
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Niches
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Ecosystem services- gator holes, mounds,
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Keystone species
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Endangered and threatened species
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Alligator farms
predation, clear vegetation…
Fig. 6-1, p. 108
Key Concepts
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Factors determining number of species in a
community
Roles of species
Species interactions
Responses to changes in environmental
conditions
Reproductive patterns
Major impacts from humans
Sustainable living
Community Structure and
Species Diversity

Physical appearance
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Edge effects
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Species diversity or richness
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Species abundance or evenness
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Niche structure
Species Diversity and Ecological
Stability
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Many different species provide ecological stability
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Some exceptions
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Minimum threshold of species diversity (10 - 40 producer species?)
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Many unknowns
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Net primary productivity (NPP)
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Essential and nonessential species
Animation
Species diversity by latitude
Types of Species

Native
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Nonnative (invasive or alien)
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Indicator-
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Keystone -
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Foundation
Indicator Species
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Provide early warnings of ecosystem damage
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Indicator of water quality (trout)
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Birds as environmental indicators (affected by
habitat loss, chemicals)
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Butterflies
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Amphibians
Amphibians as Indicator Species
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Environmentally sensitive life cycle
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Vulnerable eggs and skin- susceptible to UV,
chemicals
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Declining populations- 25% extinct or
vulnerable - why?
Life Cycle of a Frog
Young frog
Adult frog
(3 years)
sperm
Tadpole develops into
frog
Sexual
reproduction
Eggs
Fertilized egg
development Organ formation
Tadpole
Egg hatches
Fig. 6-3, p. 112
Possible Causes of Declining
Amphibian Populations

Habitat loss and fragmentation (wetland loss, deforestation,…)
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Prolonged drought
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Pollution
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Increases in ultraviolet radiation
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Parasites
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Overhunting - frog legs anyone?
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Disease
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Nonnative species - predators & competitors
Why Should We Care about
Vanishing Amphibians?
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Indicator of environmental health
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Important ecological roles of amphibians
(insect control)

Genetic storehouse for pharmaceuticals
(painkillers, antibiotics, burn & heart disease medicines)
Keystone Species

What is a keystone?
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Keystone species play critical ecological roles
a. Pollination
b. Top predators
c. decomposition

EXAMPLES: Dung beetles, Sharks, bees, bats,
wolves, alligators,
Why are Sharks Important?

Ecological roles of sharks
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Shark misconceptions
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Human deaths and injuries (p. 113)- (sharks kill 7 people /yr globally)
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Lightning is more dangerous than sharks
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Shark hunting and shark fins ($10K for a shark fin???)
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Mercury contamination
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Medical research
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Declining populations- (90 of 370 species endangered or threatened)
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Hunting bans: effective?
Foundation Species
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Relationship to keystones species
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Play important roles in shaping communities
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Elephants
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Contributions of bats and birds
Species Interactions
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Interspecific competition
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Predation
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Symbiosis= close long term association 2 or more species
A. Parasitism + B. Mutualism + +
C.Commensalism + 0
Animation
Types of two species interactions animation.
Animation
Gause's competition experiment interaction
Number of individuals
Resource Partitioning and Niche
Specialization
Species 1
Species 2
Region
of
niche overlap
Number of individuals
Resource use
Species 1
Species 2
Resource use
Fig. 6-4, p. 114
Resource Partitioning of Warbler
Species
Fig. 6-5, p. 115
Animation
Life history patterns interaction.
Animation
Capture-recapture method interaction.
How Do Predators Increase Their
Chances of Getting a Meal?
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Speed
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Senses
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Camouflage and ambush
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Chemical warfare (venom)
Avoiding and Defending Against
Predators
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Escape
Senses
Armor
Camouflage
Chemical warfare
Warning coloration
Mimicry
Behavior strategies
Safety in numbers
How Species Avoid Predators
“If it is small and strikingly beautiful, it is probably poisonous. If it is
strikingly beautiful and easy to catch, it is probably deadly.” - E.O Wilson
Span worm
Wandering leaf insect
camouflage
Poison dart frog
Bombardier beetle
Foul-tasting monarch
butterfly
Chemical warfare / Warning
Viceroy butterfly mimics
monarch butterfly
mimicry
Hind wings of io moth
resemble eyes of a
much larger animal
When touched, the
snake caterpillar
changes shape to look
like the head of a snake
Deceptive behavior
Fig. 6-6, p. 116
Parasites
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Parasitism + -
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Hosts
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Inside or outside of hosts
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Harmful effects on hosts
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Important ecological roles of parasites
Mutualism + +
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Both species benefit
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Pollination
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Benefits include nutrition and protection
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Mycorrhizae - fungi that helps plants extract
nutrients and water from soil
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Gut inhabitant mutualism
Examples of Mutualism
Oxpeckers and black rhinoceros
Mycorrhizae fungi on juniper
seedlings in normal soil
© 2006 Brooks/Cole - Thomson
Clown fish and sea anemone
Lack of mycorrhizae fungi on
juniper seedlings in sterilized soil
Fig. 6-7, p. 117
Commensalism + 0
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Species interaction that benefits one and has
little or no effect on the other
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Example: Small plants growing in shade of
larger plants
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Epiphytes
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Forehead mites
Bromeliad Commensalism
Fig. 6-8, p. 118
Ecological Succession:
Communities in Transition
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What is ecological succession?
(Gradual change in species composition)
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Primary succession = establishment of communities
on nearly lifeless ground (no soil) ex. glacier retreat, landslide,
lava, abandoned parking lot
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Secondary succession- community disturbed, soil
remains. Burned / cut forests, polluted stream, flood
Animation
Two types of ecological succession animation.
How Predictable is Succession?
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Climax community concept- orderly sequence-
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“Balance of nature”- old school
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New views of equilibrium in nature-
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Unpredictable succession- “The modern view is that we cannot
project the course of a given succession….”
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Natural struggles
Population Dynamics: Factors
Affecting Population Size
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Population change = (births + immigration)
– (deaths + emigration)
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Age structure (stages)
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Age and population stability
Limits on Population Growth
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Biotic potential
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Intrinsic rate of increase (r) (assumes unlimited resources)
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No indefinite population growth
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Environmental resistance= all the factors that limit population
(capacity for growth)
growth
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Carrying capacity (K) - determined by biotic potential & enviro
resistance
Population Growth Curves
Population size (N)
Environmental
resistance
Carrying capacity (K)
Biotic
potential
Exponential
growth
Time (t)
Fig. 6-11, p. 121
Exponential and Logistic
Population Growth
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Resources control population growth
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Exponential growth - J-shaped curve
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Logistic growth - S-shaped curve
Logistic Growth of Sheep Population
Number of sheep (millions)
2.0
Overshoot
Carrying Capacity
1.5
1.0
.5
1800
1825
1850
1875
1900
1925
Year
Fig. 6-12, p. 121
When Population Size Exceeds
Carrying Capacity
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Switch to new resources, move or die
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Overshoots
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Reproductive time lag
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Population dieback or crash
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Human Famines -
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Factors controlling human carrying capacity- technology
Irish potato famine 1845 - 1 million dead
has increased carrying capacity for humans
Number of sheep (millions)
Exponential Growth, Overshoot and
Population Crash of Reindeer
Population
Overshoots
Carrying
Capacity
2,000
Population
crashes
1,500
1,000
500
Carrying
capacity
0
1910
1920
1930
1940
1950
Year
Fig. 6-13, p. 122
Reproductive Patterns
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r-selected species
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Opportunists (mostly r-selected)
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Environmental impacts on opportunists
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K-selected species (competitors)
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Intermediate and variable reproductive patterns
r-selected Opportunists and K-selected Species
Fig. 6-15, p. 123
Positions of r-selected and K-selected
Species on Population Growth Curve
Number of individuals
Carrying capacity
K
K species;
experience
K selection
Number of individuals
r species;
experience
r selection
Time
Fig. 6-14, p. 122
Human Impacts on Ecosystems
Natural Capital Degradation
Altering Nature to Meet Our Needs
Reduction of biodiversity
Increasing use of the earth's
net primary productivity
Increasing genetic resistance
of pest species and disease
causing bacteria
Elimination of many natural
predators
Deliberate or accidental
introduction of potentially
harmful species into
communities
Using some renewable
resources faster than they can
be replenished
Interfering with the earth's
chemical cycling and energy
flow processes
Relying mostly on polluting
fossil fuels
Fig. 6-17, p. 125
Four Principles of Sustainability
PRINCIPLES
OF
SUSTAINABILITY
Fig. 6-18, p. 126
Solutions
Principles of Sustainability
How Nature Works
Solutions:
Implications
of the Principles
of Sustainability
Runs on
renewable
solar energy.
Rely mostly on
renewable solar
energy.
Recycles
nutrients
and wastes.
There is little
waste
in nature.
Prevent and
reduce
pollution and
recycle
and reuse
resources.
Uses biodiversity
to maintain itself
and adapt to new
environmental
conditions.
Preserve
biodiversity
by protecting
ecosystem
services and
preventing
premature
extinction
of species.
Controls a
species'
population size
and resource use
by interactions
with its
environment
and other
species.
Fig. 6-19, p. 126
Lessons for Us
Reduce births
and
wasteful resource
use to prevent
environmental
overload and
depletion and
degradation of
resources.
Lessons from Nature
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We are dependent on the Earth and Sun
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Everything is interdependent with everything else
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We can never do just one thing
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Earth’s natural capital must be sustained
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Precautionary Principle
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Prevention is better than cure
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Risks must be taken
Animation
Resources depletion and degradation interaction
Animation
Area and distance effects interaction.