ch7 community ecology pdf - mrrubey.files.wordpress.com course of succession cannot be precisely...
TRANSCRIPT
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Chapter 7
Community Ecology
Chapter Overview Questions
Ø What determines the number of species in a community?
Ø How can we classify species according to their roles in a community?
Ø How do species interact with one another? Ø How do communities respond to changes in
environmental conditions? Ø Does high species biodiversity increase the
stability and sustainability of a community?
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Core Case Study: Why Should We Care about the
American Alligator? Ø Hunters wiped out
population to the point of near extinction.
Ø Alligators have important ecological role.
Figure 7-1
Core Case Study: Why Should We Care about the
American Alligator? Ø Dig deep depressions (gator holes).
l Hold water during dry spells, serve as refuges for aquatic life.
Ø Build nesting mounds. l provide nesting and feeding sites for birds. l Keeps areas of open water free of vegetation.
Ø Alligators are a keystone species: l Help maintain the structure and function of the
communities where it is found.
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COMMUNITY STRUCTURE AND SPECIES DIVERSITY
Ø Biological communities differ in their structure and physical appearance.
Figure 7-2
Species Diversity and Niche Structure: Different Species Playing
Different Roles
Ø Biological communities differ in the types and numbers of species they contain and the ecological roles those species play. l Species diversity: the number of different
species it contains (species richness) combined with the abundance of individuals within each of those species (species evenness).
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Species Diversity and Niche Structure
Ø Niche structure: how many potential ecological niches occur, how they resemble or differ, and how the species occupying different niches interact.
Ø Geographic location: species diversity is highest in the tropics and declines as we move from the equator toward the poles.
TYPES OF SPECIES
Ø Native, nonnative, indicator, keystone, and foundation species play different ecological roles in communities. l Native: those that normally live and thrive in a
particular community. l Nonnative species: those that migrate,
deliberately or accidentally introduced into a community.
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Case Study: Species Diversity on Islands
Ø MacArthur and Wilson proposed the species equilibrium model or theory of island biogeography in the 1960’s.
Ø Model projects that at some point the rates of immigration and extinction should reach an equilibrium based on: l Island size l Distance to nearest mainland
Indicator Species: Biological Smoke Alarms
Ø Species that serve as early warnings of damage to a community or an ecosystem. l Presence or absence of trout species because
they are sensitive to temperature and oxygen levels.
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Keystone Species: Major Players
Ø Keystone species help determine the types and numbers of other species in a community thereby helping to sustain it.
Figures 7-4 and 7-5
Foundation Species: Other Major Players
Ø Expansion of keystone species category. Ø Foundation species can create and enhance
habitats that can benefit other species in a community. l Elephants push over, break, or uproot trees,
creating forest openings promoting grass growth for other species to utilize.
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Case Study: Why are Amphibians Vanishing?
Ø Frogs serve as indicator species because different parts of their life cycles can be easily disturbed. Figure 7-3
Case Study: Why are Amphibians Vanishing?
Ø Habitat loss and fragmentation. Ø Prolonged drought. Ø Pollution. Ø Increases in ultraviolet radiation. Ø Parasites. Ø Viral and Fungal diseases. Ø Overhunting. Ø Natural immigration or deliberate introduction
of nonnative predators and competitors.
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How Would You Vote?
To conduct an instant in-class survey using a classroom response system, access “JoinIn Clicker Content” from the PowerLecture main menu for Living in the Environment.
Ø Do we have an ethical obligation to protect shark species from premature extinction and treat them humanely? l a. No. It's impractical to force international laws on
individual fishermen that are simply trying to feed their families with the fishing techniques that they have.
l b. Yes. Sharks are an important part of marine ecosystems. They must be protected and, like all animals, they should be humanely treated.
SPECIES INTERACTIONS: COMPETITION AND PREDATION
Ø Species can interact through competition, predation, parasitism, mutualism, and commensalism.
Ø Some species evolve adaptations that allow them to reduce or avoid competition for resources with other species (resource partitioning).
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Resource Partitioning
Ø Each species minimizes competition with the others for food by spending at least half its feeding time in a distinct portion of the spruce tree and by consuming somewhat different insect species.
Figure 7-7
Niche Specialization
Ø Niches become separated to avoid competition for resources.
Figure 7-6
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SPECIES INTERACTIONS: COMPETITION AND PREDATION
Ø Species called predators feed on other species called prey.
Ø Organisms use their senses their senses to locate objects and prey and to attract pollinators and mates.
Ø Some predators are fast enough to catch their prey, some hide and lie in wait, and some inject chemicals to paralyze their prey.
PREDATION
Ø Some prey escape their predators or have outer protection, some are camouflaged, and some use chemicals to repel predators.
Figure 7-8
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SPECIES INTERACTIONS: PARASITISM, MUTUALISM, AND
COMMENSALIM Ø Parasitism occurs when one species feeds
on part of another organism. Ø In mutualism, two species interact in a way
that benefits both. Ø Commensalism is an interaction that benefits
one species but has little, if any, effect on the other species.
Parasites: Sponging Off of Others
Ø Although parasites can harm their hosts, they can promote community biodiversity. l Some parasites live in host (micororganisms,
tapeworms). l Some parasites live outside host (fleas, ticks,
mistletoe plants, sea lampreys). l Some have little contact with host (dump-nesting
birds like cowbirds, some duck species)
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Mutualism: Win-Win Relationship
Ø Two species can interact in ways that benefit both of them.
Figure 7-9
Commensalism: Using without Harming
Ø Some species interact in a way that helps one species but has little or no effect on the other.
Figure 7-10
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ECOLOGICAL SUCCESSION: COMMUNITIES IN TRANSITION
Ø New environmental conditions allow one group of species in a community to replace other groups.
Ø Ecological succession: the gradual change in species composition of a given area l Primary succession: the gradual establishment
of biotic communities in lifeless areas where there is no soil or sediment.
l Secondary succession: series of communities develop in places containing soil or sediment.
Primary Succession: Starting from Scratch
Ø Primary succession begins with an essentially lifeless are where there is no soil in a terrestrial ecosystem
Figure 7-11
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Secondary Succession: Starting Over with Some Help
Ø Secondary succession begins in an area where the natural community has been disturbed.
Figure 7-12
Can We Predict the Path of Succession, and is Nature in
Balance? Ø The course of succession cannot be
precisely predicted. Ø Previously thought that a stable climax
community will always be achieved. Ø Succession involves species competing for
enough light, nutrients and space which will influence it’s trajectory.
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ECOLOGICAL STABILITY AND SUSTAINABILITY
Ø Living systems maintain some degree of stability through constant change in response to environmental conditions through: l Inertia (persistence): the ability of a living system
to resist being disturbed or altered. l Constancy: the ability of a living system to keep
its numbers within the limits imposed by available resources.
l Resilience: the ability of a living system to bounce back and repair damage after (a not too drastic) disturbance.
ECOLOGICAL STABILITY AND SUSTAINABILITY
Ø Having many different species appears to increase the sustainability of many communities.
Ø Human activities are disrupting ecosystem services that support and sustain all life and all economies.