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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).
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.
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
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.