Chapter 6Chapter 6

Community Ecology, Community Ecology, Population Ecology, and Population Ecology, and

StabilityStability

Chapter Overview QuestionsChapter Overview Questions

What determines the number of species in a What determines the number of species in a community?community?

How can we classify species according to How can we classify species according to their roles in a community?their roles in a community?

How do species interact with one another?How do species interact with one another? How do communities respond to changes in How do communities respond to changes in

environmental conditions?environmental conditions? Does high species biodiversity increase the Does high species biodiversity increase the

stability and sustainability of a community?stability and sustainability of a community?

Core Case Study:Core Case Study:Why Should We Care about the Why Should We Care about the

American Alligator?American Alligator?

Hunters wiped out Hunters wiped out population to the population to the point of near point of near extinction.extinction.

Alligators have Alligators have important ecological important ecological role.role.

Core Case Study:Core Case Study:Why Should We Care about the Why Should We Care about the

American Alligator?American Alligator? Dig deep depressions (gator holes).Dig deep depressions (gator holes).

Hold water during dry spells, serve as refuges Hold water during dry spells, serve as refuges for aquatic life.for aquatic life.

Build nesting mounds.Build nesting mounds. provide nesting and feeding sites for birds.provide nesting and feeding sites for birds. Keeps areas of open water free of vegetation.Keeps areas of open water free of vegetation.

Alligators are a keystone species:Alligators are a keystone species: Help maintain the structure and function of the Help maintain the structure and function of the

communities where it is found.communities where it is found.

COMMUNITY STRUCTURE AND COMMUNITY STRUCTURE AND SPECIES DIVERSITYSPECIES DIVERSITY

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

Species Diversity and Niche Species Diversity and Niche Structure: Different Species Playing Structure: Different Species Playing

Different RolesDifferent Roles

Biological communities differ in the types and Biological communities differ in the types and numbers of species they contain and the numbers of species they contain and the ecological roles those species play.ecological roles those species play. Species diversitySpecies diversity: the number of different : the number of different

species it contains (species it contains (species richnessspecies richness) combined ) combined with the abundance of individuals within each of with the abundance of individuals within each of those species (those species (species evennessspecies evenness).).

Species Diversity and Niche StructureSpecies Diversity and Niche 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: species diversity is Geographic location: 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 poles.move from the equator toward the poles.

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.1. 1. NativeNative: those that normally live and thrive in a : those that normally live and thrive in a

particular community.particular community.

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

3. 3. Indicator SpeciesIndicator 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.

4. 4. Keystone SpeciesKeystone Species: Major Players: 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.

Foundation SpeciesFoundation 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 p. 108-109: Case Study p. 108-109: 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.

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.

SPECIES INTERACTIONSSPECIES INTERACTIONS: : COMPETITIONCOMPETITION AND AND PREDATIONPREDATION

How can species avoid competition or How can species avoid competition or predation?predation? Species can interact through competition, Species can interact through competition,

predation, parasitism, mutualism, and predation, parasitism, mutualism, and commensalism.commensalism.

Some species evolve adaptations that allow Some species evolve 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).

Resource PartitioningResource Partitioning

Each species minimizes Each species minimizes competition with the others competition with the others for food by spending at for food by spending at least half its feeding time least half its feeding time in a distinct portion of the in a distinct portion of the spruce tree and by spruce tree and by consuming somewhat consuming somewhat different insect species.different insect species.

Niche SpecializationNiche Specialization

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

SPECIES SPECIES INTERACTIONSINTERACTIONS: :

PREDATIONPREDATION Some prey escape Some prey escape

their predators or their predators or have outer have outer protection, some protection, some are camouflaged, are camouflaged, and some use and some use chemicals to repel chemicals to repel predators.predators.

(a) Span worm - camouflage

(b) Wandering leaf insect - camouflage

(c) Bombardier beetle – chemical warfare

(d) Foul-tasting monarch butterfly

(e) Poison dart frog

(f) Viceroy butterfly mimics monarch butterfly – mimicry

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

COMMENSALIMCOMMENSALIM

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

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

Commensalism Commensalism is an interaction that is an interaction that benefits one species but has little, if any, benefits one species but has little, if any, effect on the other species.effect on the 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. Some parasites live in host (micororganisms, Some parasites live in host (micororganisms,

tapeworms).tapeworms). Some parasites live outside host (fleas, ticks, Some parasites live outside host (fleas, ticks,

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

birds like cowbirds, some duck species)birds like cowbirds, some duck species)

MutualismMutualism: Win-Win Relationship: 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.

(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

CommensalismCommensalism: Using without Harming: 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.

ECOLOGICAL SUCCESSION: ECOLOGICAL SUCCESSION: COMMUNITIES IN TRANSITIONCOMMUNITIES IN TRANSITION

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

Ecological succession: the gradual change in : the gradual change in species composition of a given areaspecies composition of a given area Primary successionPrimary succession: the gradual establishment : the gradual establishment

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

Secondary successionSecondary succession: series of communities : series of communities develop in places containing soil or sediment.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 essentially lifeless are lifeless are where there is where there is no soil in a no soil in a terrestrial terrestrial ecosystemecosystem

Primary SuccessionPrimary Succession

Lichens on rocks Shrubs and grasses growin cracks created by lichen

Each stage accumulates soil and organic material that facilitates the growth of the next stage

Volcanic EruptionsVolcanic EruptionsMt. St. Helen’sMt. St. Helen’s

Pyroclastic Flow areaPyroclastic Flow area

Pre

-eru

ptio

n

1981

1985

1995

20042004

25 years after eruption

In the blast areaIn the blast area

1978 1981

1985 2004

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 natural the natural community community has been has been disturbed.disturbed.

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.

Changes in Population Size: Changes in Population Size: Entrances and ExitsEntrances and Exits

Populations increase through births and Populations increase through births and immigrationimmigration

Populations decrease through deaths and Populations decrease through deaths and emigrationemigration

Age Structure: Young Populations Age Structure: Young Populations Can Grow FastCan Grow Fast

How fast a population grows or declines How fast a population grows or declines depends on its age structure.depends on its age structure. Prereproductive agePrereproductive age: not mature enough to : not mature enough to

reproduce.reproduce. Reproductive ageReproductive age: those capable of : those capable of

reproduction.reproduction. Postreproductive agePostreproductive age: those too old to : those too old to

reproduce.reproduce.

Limits on Population Growth: Limits on Population Growth: Biotic Potential vs. Environmental Biotic Potential vs. Environmental

ResistanceResistance

No population can increase its size No population can increase its size indefinitely.indefinitely. The intrinsic rate of increase (The intrinsic rate of increase (rr) is the rate at ) is the rate at

which a population would grow if it had unlimited which a population would grow if it had unlimited resources.resources.

Carrying capacity (Carrying capacity (KK): the maximum population ): the maximum population of a given species that a particular habitat can of a given species that a particular habitat can sustain indefinitely without degrading the habitat.sustain indefinitely without degrading the habitat.

Exponential and Logistic Population Exponential and Logistic Population Growth: J-Curves and S-CurvesGrowth: J-Curves and S-Curves

Populations Populations grow rapidly with grow rapidly with ample ample resources, but resources, but as resources as resources become limited, become limited, its growth rate its growth rate slows and levels slows and levels off.off.

Exponential and Logistic Population Exponential and Logistic Population Growth: J-Curves and S-CurvesGrowth: J-Curves and S-Curves

As a population As a population levels off, it levels off, it often fluctuates often fluctuates slightly above slightly above and below the and below the carrying carrying capacity.capacity.

S-Curve

Exceeding Carrying Capacity: Move, Exceeding Carrying Capacity: Move, Switch Habits, or Decline in SizeSwitch Habits, or Decline in Size

Members of Members of populations which populations which exceed their exceed their resources will die resources will die unless they adapt or unless they adapt or move to an area with move to an area with more resources.more resources.

Exceeding Carrying Capacity: Move, Exceeding Carrying Capacity: Move, Switch Habits, or Decline in Size Switch Habits, or Decline in Size

Switch Habits: Switch Habits: Over time species may Over time species may increase their carrying capacity by developing increase their carrying capacity by developing adaptations.adaptations.

MoveMove: Some species maintain their carrying : Some species maintain their carrying capacity by migrating to other areas.capacity by migrating to other areas.

So far, technological, social, and other So far, technological, social, and other cultural changes have extended the earth’s cultural changes have extended the earth’s carrying capacity for humans.carrying capacity for humans.

Population Density and Population Population Density and Population Change: Change: Effects of CrowdingEffects of Crowding

Population density: the number of individuals Population density: the number of individuals in a population found in a particular area or in a population found in a particular area or volume.volume. A population’s density can affect how rapidly it A population’s density can affect how rapidly it

can grow or decline.can grow or decline.• e.g. biotic factors like diseasee.g. biotic factors like disease

Some population control factors are not affected Some population control factors are not affected by population density.by population density.• e.g. abiotic factors like weathere.g. abiotic factors like weather

REPRODUCTIVE PATTERNSREPRODUCTIVE PATTERNS

Some species reproduce without having sex Some species reproduce without having sex (asexual).(asexual). Offspring are exact genetic copies (clones).Offspring are exact genetic copies (clones).

Others reproduce by having sex (sexual).Others reproduce by having sex (sexual). Genetic material is mixture of two individuals.Genetic material is mixture of two individuals. DisadvantagesDisadvantages: males do not give birth, increase : males do not give birth, increase

chance of genetic errors and defects, courtship chance of genetic errors and defects, courtship and mating rituals can be costly.and mating rituals can be costly.

Major advantagesMajor advantages: genetic diversity, offspring : genetic diversity, offspring protection.protection.

Sexual Reproduction: CourtshipSexual Reproduction: Courtship

Courtship rituals Courtship rituals consume time and consume time and energy, can transmit energy, can transmit disease, and can disease, and can inflict injury on males inflict injury on males of some species as of some species as they compete for they compete for sexual partners.sexual partners.

Reproductive Patterns:Reproductive Patterns:Opportunists and CompetitorsOpportunists and Competitors

Large number of Large number of smaller offspring with smaller offspring with little parental care little parental care (r-(r-selected species)selected species)..

Fewer, larger Fewer, larger offspring with higher offspring with higher invested parental invested parental care care (K-selected (K-selected species).species).

Reproductive PatternsReproductive Patterns

r-selected species tend to be opportunists r-selected species tend to be opportunists while K-selected species tend to be while K-selected species tend to be competitors.competitors.

Many small offspring

Little or no parental care and protection of offspring

Early reproductive age

Most offspring die before reaching reproductive age

Small adults

Adapted to unstable climate and environmental conditions

High population growth rate (r)

Population size fluctuates wildly above and below carrying capacity (K)

Generalist niche

Low ability to compete

Early successional species

r-Selected SpeciesCockroach

Dandelion

Fewer, larger offspring

High parental care and protection of offspring

Later reproductive age

Most offspring survive to reproductive age

Larger adults

Adapted to stable climate and environmental conditions

Lower population growth rate (r)

Population size fairly stable and usually close to carrying capacity (K)

Specialist niche

High ability to compete

Late successional species

K-Selected Species

SaguaroElephant

Case Study: Exploding White-Tailed Case Study: Exploding White-Tailed Deer Populations in the United StatesDeer Populations in the United States

Since the 1930s the white-tailed deer Since the 1930s the white-tailed deer population has exploded in the United States.population has exploded in the United States. Nearly extinct prior to their protection in 1920’s.Nearly extinct prior to their protection in 1920’s.

Today 25-30 million white-tailed deer in U.S. Today 25-30 million white-tailed deer in U.S. pose human interaction problems.pose human interaction problems. Deer-vehicle collisions (1.5 million per year).Deer-vehicle collisions (1.5 million per year). Transmit disease (Lyme disease in deer ticks).Transmit disease (Lyme disease in deer ticks).