Chapter 7
Community Ecology
Chapter Overview Questions
 What
determines the number of species in a
community?
 How can we classify species according to
their roles in a community?
 How do species interact with one another?
 How do communities respond to changes in
environmental conditions?
 Does high species biodiversity increase the
stability and sustainability of a community?
Updates Online
The latest references for topics covered in this section can be found at
the book companion website. Log in to the book’s e-resources page at
www.thomsonedu.com to access InfoTrac articles.

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InfoTrac: California's wild crusade. Virginia Morell. National
Geographic, Feb 2006 v209 i2 p80(16).
InfoTrac: Traveling green. Carol Goodstein. Natural History,
July-August 2006 v115 i6 p16(4) .
InfoTrac: Too hot to trot. Charlie Furness. Geographical,
May 2006 v78 i5 p51(7).
The Nature Conservancy: Jaguar Habitat and Center of
Maya Civilization Protected in Historic Land Deal
National Geographic News: Conservationists Name Nine
New "Biodiversity Hotspots"
Core Case Study:
Why Should We Care about the
American Alligator?
 Hunters
wiped out
population to the
point of near
extinction.
 Alligators have
important ecological
role.
Figure 7-1
Core Case Study:
Why Should We Care about the
American Alligator?
 Dig

deep depressions (gator holes).
Hold water during dry spells, serve as refuges
for aquatic life.
 Build


nesting mounds.
provide nesting and feeding sites for birds.
Keeps areas of open water free of vegetation.
 Alligators

are a keystone species:
Help maintain the structure and function of the
communities where it is found.
Endangered Species
– American Alligator listed as
endangered
 By 1977 – reduced listing to threatened
 Now there are farms that provide alligator
meat and skin
 There are invasive species that threaten the
alligators: breeding populations of burmese
pythons in Florida
 1967
COMMUNITY STRUCTURE AND
SPECIES DIVERSITY
 Biological
communities differ in their structure
and physical appearance.
Figure 7-2
Tropical Coniferous Deciduous Thorn
rain forest
forest
forest
forest
Thorn
scrub
Tall-grassShort-grass Desert
scrub
prairie
prairie
Fig. 7-2, p. 144
Species Diversity and Niche Structure:
Different Species Playing Different Roles
 Biological
communities differ in the types and
numbers of species they contain and the
ecological roles those species play.

Species diversity/ species richness
• the number of different species it contains

species evenness
• combined with the abundance of individuals within each
of those species

Do you have equal numbers of different species?
The Edges
 Community


structure varies around the edges
How?
Might be sunnier, warmer, drier than forest
interior
 Increasing
edges with habitat fragmentation
increases stress on organisms



How?
Species more vulnerable to predators and fire
Can create barriers to colonizing new areas,
finding mates and food
Species Diversity and Niche Structure
 Niche



structure:
how many potential ecological niches occur?
how they resemble or differ?
how the species occupying different niches
interact?
 Geographic

location:
species diversity is highest in the tropics and
declines as we move from the equator toward the
poles.
TROPIC
 Consistent
daily climate and reliable food
sources results in specialists with narrow
niches versus generalists
 Species
in higher latitudes with variable
weather have adaptations that allow them to
survive in a greater range of environments
TYPES OF SPECIES
 Native,
nonnative, indicator, keystone, and
foundation species play different ecological
roles in communities.

Native:
• those that normally live and thrive in a particular
community.

Nonnative species:
• those that migrate, deliberately or accidentally
introduced into a community.
• Also known as invasive
Purposely introducing nonnatives
 1957
the African bee was introduced to
increase the productivity of honey bees
 This introduction created “The killler bees”
 They have migrated North but are limited by
cold weather.
 Theses bees are overly aggressive compared
with commercial honey bees
CANE TOAD
 We
will watch a video that discusses the
affects of the CANE TOAD introduced in
Australia
Case Study:
Species Diversity on Islands
 MacArthur
and Wilson proposed the species
equilibrium model or theory of island
biogeography in the 1960’s.
 Model projects that at some point the rates of
immigration and extinction should reach an
equilibrium based on:


Island size
Distance to nearest mainland
Possible Author for Book
 E.
O. Wilson
 Main works

The Theory of Island Biogeography, 1967, Princeton University Press (2001
reprint), ISBN 0-691-08836-5, with Robert H. MacArthur
 The Insect Societies, 1971, Harvard University Press, ISBN 0-674-45490-1
 Sociobiology: The New Synthesis 1975, Harvard University Press, (Twenty-fifth
Anniversary Edition, 2000

ISBN 0-674-00089-7)
On Human Nature, 1979, Harvard University Press, ISBN 0-674-01638-6
 Genes, Mind and Culture: The coevolutionary process, 1981, Harvard University
Press, ISBN 0-674-34475-8
 Promethean fire: reflections on the origin of mind, 1983, Harvard University
Press, ISBN 0-674-71445-8
 Biophilia, 1984, Harvard University Press, ISBN 0-674-07441-6

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








Success and Dominance in Ecosystems: The Case of the Social Insects, 1990, Inter-Research, ISSN
0932-2205
The Ants, 1990, Harvard University Press, ISBN 0-674-04075-9, Winner of the Pulitzer Prize, with Bert
Hölldobler
The Diversity of Life, 1992, Harvard University Press, ISBN 0-674-21298-3, The Diversity of Life: Special
Edition, ISBN 0-674-21299-1
The Biophilia Hypothesis, 1993, Shearwater Books, ISBN 1-55963-148-1, with Stephen R. Kellert
Journey to the Ants: A Story of Scientific Exploration, 1994, Harvard University Press, ISBN 0-67448525-4, with Bert Hölldobler
Naturalist, 1994, Shearwater Books, ISBN 1-55963-288-7
In Search of Nature, 1996, Shearwater Books, ISBN 1-55963-215-1, with Laura Simonds Southworth
Consilience: The Unity of Knowledge, 1998, Knopf, ISBN 0-679-45077-7
The Future of Life, 2002, Knopf, ISBN 0-679-45078-5
Pheidole in the New World: A Dominant, Hyperdiverse Ant Genus, 2003, Harvard University Press,
ISBN 0-674-00293-8
From So Simple a Beginning: Darwin's Four Great Books. 2005, W. W. Norton.
The Creation: An Appeal to Save Life on Earth, September 2006, W. W. Norton & Company, Inc. ISBN
978-0393062175
Nature Revealed: Selected Writings 1949-2006, Johns Hopkins University Press, Baltimore. ISBN 08018-8329-6
The Superorganism: The Beauty, Elegance, and Strangeness of Insect Societies, 2009, W.W. Norton &
Company, Inc. ISBN 978-0-393-06704-0, with Bert Hölldobler
Indicator Species:
Biological Smoke Alarms
Species that serve as early warnings of
damage to a community or an ecosystem.




Presence or absence of trout species because
they are sensitive to temperature and oxygen
levels.
Birds are affected quickly by change
Butterflies are associated with certain plants
Coal miners used to use canaries
• If they stopped singing then its time to get out!!!
Keystone Species: Major Players
 Keystone
species help determine the types
and numbers of other species in a
community thereby helping to sustain it.

How were Yellowstone wolves a keystone
species?
Figures 7-4 and 7-5
Case Study:
Why are Amphibians Vanishing?
 Frogs
serve as indicator species because
different parts of their life cycles can be easily
disturbed.
Figure 7-3
Adult frog
(3 years)
Sperm
Young frog
Tadpole develops
into frog
Sexual
Reproduction
Eggs
Tadpole
Fertilized egg
Egg hatches
development Organ formation
Fig. 7-3, p. 147
Case Study: Why are Amphibians
Vanishing?
 Frogs



Eggs absorb UV radiation or pollution
Tadpoles live in water and eat plants
As adults they eat insects (pesticide exposure)
 Frogs



sensitive at various stage of life
have thin permeable skin
Easily absorb pollutants from water, air, soil
As of 2004 33% of populations threatened
43% of populations declining
Case Study:
Why are Amphibians Vanishing?
 See
answers on next slide
FROGS: No single cause has
been indentified
1.
Habitat loss and fragmentation

2.
3.
Prolonged drought: kills tadpoles
Pollution

4.
Draining and filling wetlands, deforestation,
development
Pesticides = sensitivity to bacterial, viral and
fungal diseases and cause sexual abnormalities
Increases in ultraviolet radiation from ozone
layer destruction

Harms embryos of amphibians in shallow ponds
Frogs continued
5.
6.
Parasistes
Viral and Fungal diseases

7.
Climate Change:
5.
8.
9.
Chytrid fungus attacks the skin
Evaporated water increases cloud cover, lowers
daytime temps and warms night = chytrid fungi
Overhunting (Frog leg delicacy in Asia and
France)
Natural immigration or deliberate
introduction of nonnative predators +
competitors
Why should we care if frogs die?
 They
signal degradation of habitat
 They eat insects
 They are genetic storehouse of
pharmaceutical products waiting to be
discovered

Painkillers, antibiotics, burns, heart disease, etc
 They
might not need us, but we need them
Video: Frogs Galore
PLAY
VIDEO

From ABC News, Biology in the Headlines, 2005 DVD.
Foundation Species:
Other Major Players
 Expansion
of keystone species category.
 Foundation species can create and enhance
habitats that can benefit other species in a
community.



Elephants push over, break, or uproot trees,
creating forest openings promoting grass growth
for other species to utilize.
Bats and birds regenerate deforested areas
(how?)
Beavers create wetlands
How Would You Vote?
To conduct an instant in-class survey using a classroom response
system, access “JoinIn Clicker Content” from the PowerLecture main
menu for Living in the Environment.

Do we have an ethical obligation to protect shark
species from premature extinction and treat them
humanely?


a. No. It's impractical to force international laws on
individual fishermen that are simply trying to feed their
families with the fishing techniques that they have.
b. Yes. Sharks are an important part of marine
ecosystems. They must be protected and, like all
animals, they should be humanely treated.
Sharks
 Whale
shark dorsal fin can = $10,000
 Bowl of soup can = $100
 Yet fins found to be high in MERCURY
 Sharks killed because we fear them, yet only
7 people per year on average die from sharks
 SHARKS are our key to cancer.
 Sharks rarely get cancer and have effective
immune systems
 They grow slow, mature late =

SENSITIVE TO OVERFISHING
SPECIES INTERACTIONS:
COMPETITION AND PREDATION
 Species
can interact through competition,
predation, parasitism, mutualism, and
commensalism.
 Some species evolve adaptations that
allow them to reduce or avoid competition
for resources with other species (resource
partitioning).
Resource Partitioning
 Each
species minimizes
competition with the others
for food by spending at
least half its feeding time
in a distinct portion of the
spruce tree and by
consuming somewhat
different insect species.
Figure 7-7
Niche Specialization
 Niches
become
separated to
avoid competition
for resources.
Figure 7-6
Number of individuals
Number of individuals
Species 1 Species 2
Region
of
niche overlap
Resource use
Species 1
Resource use
Species 2
Fig. 7-6, p. 150
Examples
 The
lion eats larger animals and leopards eat
the smaller animals when both exist in the
same habitat.
 Hawks hunt by day and Owls hunt the same
prey by night.
SPECIES INTERACTIONS:
COMPETITION AND PREDATION
 Species
called predators feed on other
species called prey.
 Organisms use their senses their senses to
locate objects and prey and to attract
pollinators and mates.
 Some predators are fast enough to catch their
prey, some hide and lie in wait, and some
inject chemicals to paralyze their prey.
PREDATION
 Some
prey escape
their predators or
have outer
protection, some
are camouflaged,
and some use
chemicals to repel
predators.
Figure 7-8
Camouflage
(a) Span worm
Fig. 7-8a, p. 153
Camouflage
(b) Wandering leaf insect
Fig. 7-8b, p. 153
Chemical
Warfare
(c) Bombardier beetle
Fig. 7-8c, p. 153
Chemical Warfare
Warning
coloration
(d) Foul-tasting monarch butterfly
Fig. 7-8d, p. 153
Chemical Warfare
Warning
coloration
(e) Poison dart frog
Fig. 7-8e, p. 153
mimicry
(f) Viceroy butterfly mimics
monarch butterfly
Fig. 7-8f, p. 153
(g) Hind wings of Io moth
resemble eyes of a much
larger animal.
Fig. 7-8g, p. 153
Deceptive
Behavior
(h) When touched, snake
caterpillar changes shape
to look like head of snake.
Fig. 7-8h, p. 153
SPECIES INTERACTIONS:
PARASITISM, MUTUALISM, AND
COMMENSALIM
 Parasitism
occurs when one species feeds
on part of another organism.
 In mutualism, two species interact in a way
that benefits both.
 Commensalism is an interaction that benefits
one species but has little, if any, effect on the
other species.
Parasites: Sponging Off of Others
 Although
parasites can harm their hosts, they
can promote community biodiversity.



Some parasites live in host (micororganisms,
tapeworms).
Some parasites live outside host (fleas, ticks,
mistletoe plants, sea lampreys).
Some have little contact with host (dump-nesting
birds like cowbirds, some duck species)
Mutualism: Win-Win Relationship
 Two
species
can interact in
ways that
benefit both of
them.
Figure 7-9
(a) Oxpeckers and black rhinoceros
Fig. 7-9a, p. 154
(b) Clownfish and sea anemone
Fig. 7-9b, p. 154
(c) Mycorrhizal fungi on juniper seedlings
in normal soil
Fig. 7-9c, p. 154
(d) Lack of mycorrhizal fungi on juniper seedlings
in sterilized soil
Fig. 7-9d, p. 154
Mutualism
• The microorganisms in our digestive tract
and other guts help digest food and benefit
from a sheltered habitat with a consistent
food supply
• Without termites there would not be a
decay of cellulose. Termites have bacteria
and protozoan that help them breakdown
cellulose (tough carbohydrates in plants)
Commensalism: Using without Harming
 Some
species
interact in a way
that helps one
species but has
little or no effect
on the other.
Figure 7-10
EPIPHYTES
 Some
orchids grow in the branches of other
trees.
 They appear to not harm their host tree.
ECOLOGICAL SUCCESSION:
COMMUNITIES IN TRANSITION
 New
environmental conditions allow one
group of species in a community to replace
other groups.
 Ecological succession: the gradual change
in species composition of a given area


Primary succession: the gradual establishment
of biotic communities in lifeless areas where
there is no soil or sediment.
Secondary succession: series of communities
develop in places containing soil or sediment.
Primary Succession:
Starting from Scratch
 Primary
succession
begins with an
essentially
lifeless are
where there is
no soil in a
terrestrial
ecosystem
Figure 7-11
Started on new islands,
melted glaciers, after
volcanic eruptions
Succession is
dependent on climate
Lichens
Exposed
and mosses
rocks
Fig. 7-11, p. 156
Secondary Succession:
Starting Over with Some Help
 Secondary
succession
begins in an
area where
the natural
community
has been
disturbed.
Figure 7-12
Fig. 7-12, p. 157
Can We Predict the Path of
Succession, and is Nature in
Balance?
 The
course of succession cannot be
precisely predicted.
 Previously thought that a stable climax
community will always be achieved.
 Succession involves species competing for
enough light, nutrients and space which will
influence it’s trajectory.
ECOLOGICAL STABILITY AND
SUSTAINABILITY
 Living
systems maintain some degree of
stability through constant change in response
to environmental conditions through:

Inertia (persistence):
• the ability of a living system to resist being disturbed or
altered.

Constancy:
• the ability of a living system to keep its numbers within
the limits imposed by available resources.

Resilience:
• the ability of a living system to bounce back and repair
damage after (a not too drastic) disturbance.
ECOLOGICAL STABILITY AND
SUSTAINABILITY
 Having
many different species appears to
increase the sustainability of many
communities.
 Human activities are disrupting ecosystem
services that support and sustain all life and
all economies.