Chapter 8

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?

Core Case Study:Why Should We Care about the

American Alligator?• Hunters wiped out

population to the point of near ________.

• Alligators have important ecological role.

Core Case Study:Why Should We Care about the

American Alligator?• Dig deep depressions (__________).– Hold water during dry spells, serve as refuges for

aquatic life.• Build _________ _________.– provide nesting and feeding sites for birds.– Keeps areas of open water free of vegetation.

• Alligators are a __________ species:– Help maintain the structure and function of the

communities where it is found.

COMMUNITY STRUCTURE AND SPECIES DIVERSITY

• Biological communities differ in their structure and physical appearance.

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 __________ the number of different species

it contains (species __________) combined with the abundance of individuals within each of those species (species _________).

Species Diversity and Niche Structure

• Niche structure: how many potential __________ _______occur, how they resemble or differ, and how the species occupying different niches interact.

• Geographic location: species _______ is highest in the tropics and declines as we move from the ________ toward the _______.

TYPES OF SPECIES

• Native, nonnative, indicator, keystone, and foundation species play different ecological roles in communities.– _________ ________: those that normally live and

thrive in a particular community.– __________ _______: those that migrate,

deliberately or accidentally introduced into a community.

Case Study:Species Diversity on Islands

• MacArthur and Wilson proposed the species equilibrium model or ______ __ _______ ___________ in the 1960’s.

• Model projects that at some point the rates of immigration and extinction should reach an __________ based on:– Island size– Distance to nearest mainland

Indicator Species: Biological Smoke Alarms

• Species that serve as ______ ________ of damage to a community or an ecosystem.– Presence or absence of trout species because they

are sensitive to temperature and oxygen levels.

Keystone Species: Major Players

• Keystone species help determine the _____ and ________ of other species in a community thereby helping to sustain it.

Foundation Species: Other Major Players

• Expansion of keystone species category.• Foundation species can ______ and

______habitats that can benefit other species in a community.– _________ push over, break, or uproot trees, creating

forest openings promoting grass growth for other species to utilize.

Case Study: Why are Amphibians Vanishing?

• Frogs serve as indicator species because different parts of their life cycles can be easily disturbed.

Young frogAdult frog(3 years)

Sperm

SexualReproduction

Eggs Fertilized eggdevelopment Organ formation

Egg hatches

Tadpole

Tadpole developsinto frog

Case Study: Why are Amphibians Vanishing?

• Habitat loss and __________.• Prolonged ________.• Pollution.• Increases in ________ _______.• Parasites.• ______and _______ diseases.• Overhunting.• Natural _________ or deliberate _________ of

nonnative predators and competitors.

Video: Frogs Galore

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

PLAYVIDEO

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.

SPECIES INTERACTIONS: COMPETITION AND PREDATION

• Species can ________ through competition, predation, parasitism, mutualism, and commensalism.

• Some species ________ __________that allow them to reduce or avoid competition for resources with other species (________ __________).

Resource Partitioning

• Each species _________ competition with the others for _______ by spending at least half its feeding time in a distinct portion of the spruce tree and by consuming somewhat ________ ______ _______.

Niche Specialization

• Niches become separated to avoid ________ for _______.

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

SPECIES INTERACTIONS: COMPETITION AND PREDATION

• Species called ________ feed on other species called prey.

• Organisms use their _________to locate objects and ______ and to attract pollinators and mates.

• Some _________ are fast enough to catch their ______, some hide and lie in wait, and some inject _________ to paralyze their prey.

PREDATION

• Some prey escape their predators or have outer protection, some are ________, and some use chemicals to repel predators.

(a) Span worm

(b) Wandering leaf insect

(c) Bombardier beetle

(d) Foul-tasting monarch butterfly

(e) Poison dart frog

(f) Viceroy butterfly mimics monarch butterfly

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

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

SPECIES INTERACTIONS: PARASITISM, MUTUALISM, AND COMMENSALIM

• _________ occurs when one species feeds on part of another organism.

• In _________, two species interact in a way that benefits both.

• __________ is an interaction that benefits one species but has little, if any, effect on the other species.

Parasites: Sponging Off of Others

• Although _________ can harm their hosts, they can promote community ________.– Some _________ live in host (microorganisms,

tapeworms).– Some parasites live outside _______ (fleas, ticks,

mistletoe plants, sea lampreys).– Some have little contact with host (dump-nesting

birds like cowbirds, some duck species)

_________: Win-Win Relationship

• Two species can interact in ways that benefit both of them.

(a) Oxpeckers and black rhinoceros

(b) Clownfish and sea anemone

(c) Mycorrhizal fungi on juniper seedlings in normal soil

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

___________: Using without Harming

• Some species interact in a way that helps one species but has little or no effect on the other.

ECOLOGICAL SUCCESSION: COMMUNITIES IN TRANSITION

• New environmental conditions allow one group of species in a community to replace other groups.

• Ecological _________: the gradual change in species composition of a given area– _________ ________: the gradual establishment of

biotic communities in lifeless areas where there is no soil or sediment.

– _________ _________ : series of communities develop in places containing soil or sediment.

________Succession: Starting from Scratch

• Primary succession begins with an essentially lifeless are where there is no soil in a terrestrial ecosystem

Exposed rocks

Lichens and mosses

Small herbs and shrubs

Heath matJack pine,

black spruce, and aspen

Balsam fir,

paper birch, and

white spruce

forest community

Time

Secondary Succession: Starting Over with Some Help

• Secondary succession begins in an area where the natural community has been disturbed.

Time

Annual

weeds

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.