Chapter 7Chapter 7

Community EcologyCommunity Ecology

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.

Figure 7-1Figure 7-1

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.

Figure 7-2Figure 7-2

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. 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.

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 7-5

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?

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.

How Would You Vote?How Would You Vote?

Do we have an ethical obligation to protect shark Do we have an ethical obligation to protect shark species from premature extinction and treat them species from premature extinction and treat them humanely?humanely?

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

Figure 7-7Figure 7-7

Niche SpecializationNiche Specialization

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

Figure 7-6Figure 7-6

SPECIES INTERACTIONS: SPECIES INTERACTIONS: COMPETITION AND PREDATIONCOMPETITION AND PREDATION

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.

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.

Figure 7-8Figure 7-8

SPECIES INTERACTIONS:SPECIES INTERACTIONS:SymbiosisSymbiosis

A relationship in which organisms from two A relationship in which organisms from two different species interact to survive.different species interact to survive.

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, tapeworms).Some parasites live in host (micororganisms, tapeworms). Some parasites live outside host (fleas, ticks, mistletoe plants, sea Some parasites live outside host (fleas, ticks, mistletoe plants, sea

lampreys).lampreys). Some have little contact with host (dump-nesting birds like cowbirds)Some have little contact with host (dump-nesting birds like cowbirds)

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.

Figure 7-9Figure 7-9

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

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 successionEcological succession: the gradual change : the gradual change in species composition of a given areain species 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

Figure 7-11Figure 7-11

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.

Figure 7-12Figure 7-12

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: Inertia (persistence): the ability of a living system Inertia (persistence): the ability of a living system

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

Resilience: the ability of a living system to Resilience: 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.