Chapter 8Chapter 8

Community EcologyCommunity Ecology

Importance of Biodiversity

Question of the DayQuestion of the Day

The best example of a tertiary consumer would The best example of a tertiary consumer would be a/anbe a/an

a.a. mousemouse

b.b. grasshoppergrasshopper

c.c. sheepsheep

d.d. cactuscactus

e.e. coyotecoyote

Section 8-1Section 8-1

Community Structure &

Species Diversity

Question to Consider

How does community structure affect species diversity?

COMMUNITY STRUCTURECOMMUNITY STRUCTURE

Biological communities differ in their structure Biological communities differ in their structure and physical appearance.and physical appearance.

Figure 8-2Figure 8-2

Physical CharacteristicsPhysical Characteristics Physical appearance: the relative sizes,

stratification, and distribution of its populations and species

Transition occurs around the edges, where two community types interact.

Increased edge area may be harmful due to habitat fragmentation; many species become more vulnerable to predators and loss of colonization ability.

Species Diversity Species Diversity

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).

Niche StructureNiche Structure

Niche structure: how many potential Niche structure: how many potential ecological niches occur, how they resemble ecological niches occur, how they resemble or differ, and how the species occupying or differ, and how the species occupying different niches interact.different niches interact.

Geographic location: Geographic location: species diversity is species diversity is highest in the tropics and declines as we highest in the tropics and declines as we move from the equator toward the polesmove from the equator toward the poles..

Species Diversity on IslandsSpecies Diversity on Islands

MacArthur and Wilson proposed the species MacArthur and Wilson proposed the species equilibrium model or theory of island equilibrium model or theory of island biogeography in the 1960’s.biogeography in the 1960’s.

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

Why? Why? Conserving Biodiversity

Section 8-2Section 8-2

Types of Species

Question to ConsiderHow does a species’ role affect biological

communities?

Question of the DayQuestion of the Day

Q: Which of the following best illustrates the concept of the tragedy of the commons? A. Destruction of landscape by surface

mining on private land B. Selective harvesting of trees by a timber

company in a national forest C. Legislation of catch limits to avoid

depletion of fish stocks in a shared lake D. Inadvertent destruction of beneficial

species while attempting to control pests E. Depletion of an aquifer by regional farmers

TYPES OF SPECIESTYPES OF SPECIES Native, nonnative, indicator, keystone, and Native, nonnative, indicator, keystone, and

foundation species play different ecological foundation species play different ecological roles in communities.roles in communities. Native: those that normally live and thrive in a Native: those that normally live and thrive in a

particular community.particular community.

Nonnative species: those that migrate, Nonnative species: those that migrate, deliberately or accidentally introduced into a deliberately or accidentally introduced into a community.community.

Kudzu

Indicator Species: Indicator Species: Biological Smoke AlarmsBiological Smoke Alarms

Species that serve as early warnings of Species that serve as early warnings of damage to a community or an ecosystem.damage to a community or an ecosystem. Presence or absence of trout species because Presence or absence of trout species because

they are sensitive to temperature and oxygen they are sensitive to temperature and oxygen levels.levels.

Keystone Species: Major PlayersKeystone Species: Major Players

Keystone species help determine the types Keystone species help determine the types and numbers of other species in a and numbers of other species in a community thereby helping to sustain it.community thereby helping to sustain it.

Figures 7-4 and 7-5Figures 7-4 and 7-5Keystone Species

Foundation Species: Foundation Species: Other Major PlayersOther Major Players

Expansion of keystone species category.Expansion of keystone species category.

Foundation species can create and enhance Foundation species can create and enhance habitats that can benefit other species in a habitats that can benefit other species in a community.community. Elephants push over, break, or uproot trees, Elephants push over, break, or uproot trees,

creating forest openings promoting grass growth creating forest openings promoting grass growth for other species to utilize.for other species to utilize.

Case Study: Case Study: Why are Amphibians Vanishing?Why are Amphibians Vanishing?

Frogs serve as indicator species because Frogs serve as indicator species because different parts of their life cycles can be easily different parts of their life cycles can be easily disturbed.disturbed. Figure 8-3Figure 8-3

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: Case Study: Why are Amphibians Vanishing?Why are Amphibians Vanishing?

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

of nonnative predators and competitors.of nonnative predators and competitors.

Section 8-3Section 8-3

Species Interactions:

Competition & Predation

Lion vs. Wildebeest

Question of the DayQuestion of the Day

Which of the following is the best example of Which of the following is the best example of a keystone species?a keystone species?

a.a. Sea otterSea otter

b.b. Sea urchinSea urchin

c.c. Spotted owlSpotted owl

d.d. Snail darterSnail darter

e.e. E. Condor E. Condor

SPECIES INTERACTIONS: SPECIES INTERACTIONS: COMPETITION AND PREDATIONCOMPETITION AND PREDATION

Species can interact through competition, Species can interact through competition, predation, parasitism, mutualism, and predation, parasitism, mutualism, and commensalism.commensalism.

Some species have adaptations that allow Some species have adaptations that allow them to reduce or avoid competition for them to reduce or avoid competition for resources with other species (resource resources with other species (resource partitioning).partitioning).

Competition:Competition:Resource PartitioningResource Partitioning

Each species minimizes Each species minimizes competition with the others competition with the others for food by for food by

1. Spending at least half its 1. Spending at least half its feeding time in a distinct feeding time in a distinct portion of the spruce tree portion of the spruce tree andand

2. By consuming somewhat 2. By consuming somewhat different insect species.different insect species.

Figure 7-7Figure 7-7

Competition: Niche SpecializationCompetition: Niche Specialization

Niches become Niches become separated to separated to avoid competition avoid competition for resourcesfor resources

Grizzlies & WolvesGrizzlies & Wolves

Figure 7-6Figure 7-6

PREDATIONPREDATION Species called predators feed on other Species called predators feed on other

species called prey.species called prey.

Organisms use their senses their senses to Organisms use their senses their senses to locate objects and prey and to attract locate objects and prey and to attract pollinators and mates.pollinators and mates.

Some predators are fast enough to catch their Some predators are fast enough to catch their prey, some hide and lie in wait, and some prey, some hide and lie in wait, and some inject chemicals to paralyze their prey.inject chemicals to paralyze their prey.

Prey adaptations Prey adaptations 1. Some prey escape their 1. Some prey escape their predators predators

Cheetah vs. Gazelle Cheetah vs. Gazelle

2. Have outer protection 2. Have outer protection

3. Some are camouflaged 3. Some are camouflaged

4. Some use chemicals to 4. Some use chemicals to repel predators.repel predators.

Figure 7-8Figure 7-8

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

Fig. 7-8b, p. 153

(b) Wandering leaf insect

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

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

Fig. 7-8e, p. 153

(e) Poison dart frog

Fig. 7-8f, p. 153

(f) Viceroy butterfly mimics monarch butterfly

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.

Section 8-3Section 8-3Summary

Competition

Predation

Section 8-4Section 8-4

SPECIES INTERACTIONS: SPECIES INTERACTIONS: PARASITISM, MUTUALISM, AND PARASITISM, MUTUALISM, AND

COMMENSALIMCOMMENSALIM

Tongue Eaters

Question of the DayQuestion of the Day

Zero population growth is associated witha.Phase I onlyb.Phase II onlyc.Phase III onlyd.Phase IV onlye.Phase I and IV

PARASITISM, MUTUALISM, AND PARASITISM, MUTUALISM, AND COMMENSALIMCOMMENSALIM

Parasitism occurs when one species feeds Parasitism occurs when one species feeds on part of another organism.on part of another organism.

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

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

Parasites: Sponging Off of OthersParasites: Sponging Off of Others Although parasites can harm their hosts, they Although parasites can harm their hosts, they

can promote community biodiversity.can promote community biodiversity.1. Some parasites live in host (micororganisms, 1. Some parasites live in host (micororganisms, tapeworms).tapeworms).

MalariaMalaria

2. Some parasites live outside host (fleas, ticks, 2. Some parasites live outside host (fleas, ticks, mistletoe plants, sea lampreys).mistletoe plants, sea lampreys).

3. Some have little contact with host (dump-nesting 3. Some have little contact with host (dump-nesting birds like cowbirds, some duck species)birds like cowbirds, some duck species)

Mutualism: Win-Win RelationshipMutualism: Win-Win Relationship

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

Unlikely Travel Unlikely Travel CompanionsCompanions

Figure 7-9Figure 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

Commensalism: Using without HarmingCommensalism: Using without Harming

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

Figure 7-10Figure 7-10

Section 8-4Section 8-4SummarySummary

Parasitism

Mutualism

Commensalism

Section 8-5 & 8-6Section 8-5 & 8-6

Ecological Succession

& Stability

Essential Question:

How do communities undergo natural change?

Mt St Helens

Question of the DayQuestion of the Day

Which of the following elements is most likely to limit primary production in freshwater lakes?

A. Oxygen

B. Calcium

C. Phosphorus

D. Carbon

E. Iron

COMMUNITIES IN TRANSITIONCOMMUNITIES 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: Primary Succession: Starting from ScratchStarting from Scratch

Primary Primary succession succession begins with an begins with an essentially lifeless essentially lifeless area, where there area, where there is no soil in a is no soil in a terrestrial terrestrial ecosystemecosystem

Figure 7-11Figure 7-11

Typical Changes Typical Changes Community changes during succession include

increases in species diversity and changes in species composition

• Characteristics of Pioneer Species:

Ecosystem changes during succession include increases in biomass, primary production, respiration, and nutrient retention.

• Modification of soil and other environmental changes lead to changes in species.

Secondary Succession: Secondary Succession: Starting Over with Some HelpStarting Over with Some Help

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

Figure 7-12Figure 7-12

Can We Predict the Can We Predict the Path of SuccessionPath of Succession

The course of succession cannot be The course of succession cannot be precisely predicted.precisely predicted.

Previously thought that a stable climax Previously thought that a stable climax community will always be achieved.community will always be achieved.

Succession involves species competing for Succession involves species competing for enough light, nutrients and space which will enough light, nutrients and space which will influence it’s trajectory.influence it’s trajectory.

ECOLOGICAL STABILITY AND ECOLOGICAL STABILITY AND SUSTAINABILITYSUSTAINABILITY

Living systems maintain some degree of Living systems maintain some degree of stability through constant change in response stability through constant change in response to environmental conditions through:to environmental conditions through: InertiaInertia (persistence): the ability of a living system (persistence): the ability of a living system

to resist being disturbed or altered.to resist being disturbed or altered. ConstancyConstancy: the ability of a living system to keep : the ability of a living system to keep

its numbers within the limits imposed by available its numbers within the limits imposed by available resources.resources.

ResilienceResilience: the ability of a living system to : the ability of a living system to bounce back and repair damage after (a not too bounce back and repair damage after (a not too drastic) disturbance.drastic) disturbance.

ECOLOGICAL STABILITY AND ECOLOGICAL STABILITY AND SUSTAINABILITYSUSTAINABILITY

Having many different species appears to Having many different species appears to increase the sustainability of many increase the sustainability of many communities.communities.

Human activities are disrupting ecosystem Human activities are disrupting ecosystem services that support and sustain all life and services that support and sustain all life and all economies.all economies.

Chapter Overview QuestionsChapter 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?