Chp 7 Miller

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.     

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"

Video: Whaling  This video clip is available in CNN Today

Videos for Environmental Science, 2004, Volume VII. Instructors, contact your local sales representative to order this volume, while supplies last.

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.

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: the number of different species it contains (species richness) combined with the abundance of individuals within each of those species (species evenness).

Species Diversity and Niche Structure  Niche structure: how many potential

ecological niches occur, how they resemble or differ, and 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.

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.

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

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.

Keystone Species: Major Players

 Keystone species help determine the types

and numbers of other species in a community thereby helping to sustain it. Figures 7-4 and 7-5

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.

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?  Habitat loss and fragmentation.  Prolonged drought.  Pollution.  Increases in ultraviolet radiation.  Parasites.  Viral and Fungal diseases.  Overhunting.  Natural immigration or deliberate introduction

of nonnative predators and competitors.

Video: Frogs Galore

PLAY VIDEO 

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

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 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

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

(a) Span worm

Fig. 7-8a, p. 153

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

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

(d) Foul-tasting monarch butterfly

Fig. 7-8d, p. 153

(e) Poison dart frog Fig. 7-8e, p. 153

(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

(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

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

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

Lichens Exposed and mosses rocks

Small herbs and shrubs

ma Heath

t

ir, Balsam hf , and birc Jack pinec, e,paperite spruce black sprpuen wh forest and as i ty commun

Time 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

l Annua weeds

ial Perenn d an weeds s grasse

Shrubs and pine seedlings

forest e n i p g n You loping e v e d h t wi ak ory of o t s r e d n u y trees r o k c i h and

forest y r o k ak-hic o e r u t Ma

Time

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.