Chapter 7Chapter 7

Community EcologyCommunity Ecology

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 American Why Should We Care about the American

Alligator?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 American Alligator?Why Should We Care about the American Alligator?

Dig deep depressions (gator holes).Dig deep depressions (gator holes). Hold water during dry spells, serve as refuges for Hold water during dry spells, serve as refuges for

aquatic life.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 SPECIES COMMUNITY STRUCTURE AND SPECIES DIVERSITYDIVERSITY

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

Fig. 7-2, p. 144

Short-grassprairie

Desertscrub

Tall-grassprairie

Thornscrub

Thornforest

Deciduousforest

Coniferousforest

Tropicalrain forest

Species Diversity and Niche Structure: Species Diversity and Niche Structure: Different Species Playing Different RolesDifferent Species Playing Different 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 species it : the number of different species it

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

Species Diversity and Niche StructureSpecies Diversity and Niche Structure

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

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

Animation: Species Diversity By Animation: Species Diversity By LatitudeLatitude

Animations/species_by_latitude.html

TYPES OF SPECIESTYPES OF SPECIES

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

particular community.particular community.

Case Study:Case Study: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

Animation: Area and Distance EffectsAnimation: Area and Distance Effects

Animations/species_equilibrium.html

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 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).

Animation: How Species InteractAnimation: How Species Interact

Animations/species_interactions.html

Resource PartitioningResource Partitioning

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

Niche SpecializationNiche Specialization

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

Animation: Gause’s Competition Animation: Gause’s Competition ExperimentExperiment

Animations/gause_v2.html

SPECIES INTERACTIONS: SPECIES INTERACTIONS: COMPETITION AND PREDATIONCOMPETITION AND PREDATION

Species called predators feed on other species Species called predators feed on other species called prey.called prey.

Organisms use their senses to locate objects and Organisms use their senses to locate objects and prey and to attract pollinators and mates.prey and to attract 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 inject prey, some hide and lie in wait, and some inject chemicals to paralyze their prey.chemicals to paralyze their prey.

PREDATIONPREDATION

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

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.

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 group of species in a community to replace other groups.replace other groups.

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

Animation: SuccessionAnimation: Succession

Animations/succession.html

Primary Succession: Primary Succession: Starting from ScratchStarting from Scratch

Primary Primary successionsuccession: the : the gradual gradual establishment of establishment of biotic communities biotic communities in lifeless areas in lifeless areas where there is no where there is no soil or sediment.soil or sediment.

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

Figure 7-Figure 7-1111

Fig. 7-11, p. 156

Exposed rocks

Lichens and mosses

Small herbs and shrubs

Heath matJack pine,

black spruce,

and aspen

Balsam fir,

paper birch, and

white spruceforest

community

Time

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

Secondary Secondary successionsuccession: : series of series of communities communities develop in develop in places places containing soil containing soil or sediment.or sediment.

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

Figure 7-Figure 7-1212

Fig. 7-12, p. 157

Time

Annual

weeds

Perennial

weeds and

grasses

Shrubs

and pine

seedlings

Young pine forest

with developing

understory of oak

and hickory trees

Mature oak-hickory forest

Can We Predict the Path of Can We Predict the Path of Succession, and is Nature in Succession, and is Nature in

Balance?Balance? 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 Succession involves species competing

for enough light, nutrients and space for enough light, nutrients and space which will influence it’s trajectory.which will 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 stability through constant change in response to environmental conditions response to environmental conditions through:through: Inertia (persistence): the ability of a living Inertia (persistence): the ability of a living

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

keep its numbers within the limits imposed keep its numbers within the limits imposed by available resources.by available 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 bounce back and repair damage after (a not too drastic) disturbance.too drastic) disturbance.

ECOLOGICAL STABILITY AND ECOLOGICAL STABILITY AND SUSTAINABILITYSUSTAINABILITY

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

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

Video: Bees PollinatingVideo: Bees Pollinating

Videos/bumblebee.html

Video: Cliff NestersVideo: Cliff Nesters

Videos/cliff_birds.html

Video: Eagle FishingVideo: Eagle Fishing

Videos/eagle_fishing.html

Video: Grizzly Bear FeedingVideo: Grizzly Bear Feeding

Videos/grizzly_feeds.html

Video: Migratory BirdsVideo: Migratory Birds

Videos/migratory_birds.html

Video: Owl HuntingVideo: Owl Hunting

Videos/owl_hunts.html

Video: Pelican ColonyVideo: Pelican Colony

Videos/pelican_colony.html

Video: SaguarosVideo: Saguaros

Videos/saguaros.html

Video: Wolf PackVideo: Wolf Pack

Videos/wolf_pack.html