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 OnlineThe 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.

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

1967 – 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

COMMUNITY STRUCTURE AND SPECIES DIVERSITY

Biological communities differ in their structure and physical appearance.

Figure 7-2

Fig. 7-2, p. 144

Short-grassprairie

Desertscrub

Tall-grassprairie

Thornscrub

Thornforest

Deciduousforest

Coniferousforest

Tropicalrain forest

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

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 0-674-48525-4, 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 0-8018-8329-6 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

Fig. 7-3, p. 147

Young frogAdult frog(3 years)

Sperm

SexualReproduction

Eggs Fertilized eggdevelopment Organ formation

Egg hatches

Tadpole

Tadpole developsinto frog

Case Study: Why are Amphibians Vanishing?

Frogs sensitive at various stage of life Eggs absorb UV radiation or pollution Tadpoles live in water and eat plants As adults they eat insects (pesticide exposure)

Frogs 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 Draining and filling wetlands, deforestation,

development2. Prolonged drought: kills tadpoles3. Pollution

Pesticides = sensitivity to bacterial, viral and fungal diseases and cause sexual abnormalities

4. Increases in ultraviolet radiation from ozone layer destruction

Harms embryos of amphibians in shallow ponds

Frogs continued5. Parasistes6. Viral and Fungal diseases

Chytrid fungus attacks the skin7. Climate Change:

5. Evaporated water increases cloud cover, lowers daytime temps and warms night = chytrid fungi

8. Overhunting (Frog leg delicacy in Asia and France)

9. 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

From ABC News, Biology in the Headlines, 2005 DVD.

PLAYVIDEO

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

Fig. 7-6, p. 150

Species 2Species 1N

umbe

r of i

ndiv

idua

lsN

umbe

r of i

ndiv

idua

ls

Species 2Species 1

Resource use

Resource use

Regionof

niche overlap

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

Fig. 7-8a, p. 153(a) Span worm

Camouflage

Fig. 7-8b, p. 153(b) Wandering leaf insect

Camouflage

Fig. 7-8c, p. 153(c) Bombardier beetle

Chemical Warfare

Fig. 7-8d, p. 153(d) Foul-tasting monarch butterfly

Chemical Warfare Warning coloration

Fig. 7-8e, p. 153

(e) Poison dart frog

Chemical Warfare

Warning coloration

Fig. 7-8f, p. 153

(f) Viceroy butterfly mimics monarch butterfly

mimicry

Fig. 7-8g, p. 153

(g) Hind wings of Io moth resemble eyes of a much larger animal.

Fig. 7-8h, p. 153

(h) When touched, snake caterpillar changes shape to look like head of snake.

Deceptive Behavior

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

Fig. 7-9a, p. 154(a) Oxpeckers and black rhinoceros

Fig. 7-9b, p. 154(b) Clownfish and sea anemone

Fig. 7-9c, p. 154

(c) Mycorrhizal fungi on juniper seedlings in normal soil

Fig. 7-9d, p. 154

(d) Lack of mycorrhizal fungi on juniper seedlings in sterilized soil

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

Fig. 7-11, p. 156

Exposed rocks

Lichens and mosses

Small herbs and shrubs

Heath matJack pine,

black spruce, and aspen

Balsam fir, paper birch, and

white spruceforest

community

Time

Started on new islands, melted glaciers, after volcanic eruptions

Succession is dependent on climate

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

TimeAnnualweeds

Perennial

weeds and

grasses

Shrubsand pineseedlings

Young pine forest

with developing

understory of oak

and hickory trees

Mature oak-hickory forest

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.