Community Ecology

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Chapter 8

• Community Ecology

Importance of Biodiversity
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Question of the Day

• The best example of a tertiary consumer would be
  a/an
• mouse
• grasshopper
• sheep
• cactus
• coyote

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Section 8-1

• Community Structure
• Species Diversity
• Question to Consider
• How does community structure affect species
  diversity?

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COMMUNITY STRUCTURE

• Biological communities differ in their structure
  and physical appearance.

Figure 8-2
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Physical Characteristics

• Physical appearance the relative sizes,
  stratification, and distribution of its
  populations and species
• Transition occurs around the edges, where two
  community types interact.
• Increased edge area may be harmful due to habitat
  fragmentation many species become more
  vulnerable to predators and loss of colonization
  ability.

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Species Diversity

• Biological communities differ in the types and
  numbers of species they contain and the
  ecological roles those species play.
• 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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Niche Structure

• Niche structure how many potential ecological
  niches occur, how they resemble or differ, and
  how the species occupying different niches
  interact.
• Geographic location species diversity is highest
  in the tropics and declines as we move from the
  equator toward the poles.

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Species Diversity on Islands

• MacArthur and Wilson proposed the species
  equilibrium model or theory of island
  biogeography in the 1960s.
• Model projects that at some point the rates of
  immigration and extinction should reach an
  equilibrium based on
• Island size
• Distance to nearest mainland
• Why?

Conserving Biodiversity
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Section 8-2

• Types of Species
• Question to Consider
• How does a species role affect biological
  communities?

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Question of the Day

• Q Which of the following best illustrates the
  concept of the tragedy of the commons?
• A. Destruction of landscape by surface mining on
  private land
• B. Selective harvesting of trees by a timber
  company in a national forest
• C. Legislation of catch limits to avoid
  depletion of fish stocks in a shared lake
• D. Inadvertent destruction of beneficial species
  while attempting to control pests
• E. Depletion of an aquifer by regional farmers

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TYPES OF SPECIES

• Native, nonnative, indicator, keystone, and
  foundation species play different ecological
  roles in communities.
• Native those that normally live and thrive in a
  particular community.
• Nonnative species those that migrate,
  deliberately or accidentally introduced into a
  community.

Kudzu
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Indicator Species Biological Smoke Alarms

• Species that serve as early warnings of damage to
  a community or an ecosystem.
• Presence or absence of trout species because they
  are sensitive to temperature and oxygen levels.

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Keystone Species Major Players

• Keystone species help determine the types and
  numbers of other species in a community thereby
  helping to sustain it.

Keystone Species
Figures 7-4 and 7-5
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Foundation Species Other Major Players

• Expansion of keystone species category.
• Foundation species can create and enhance
  habitats that can benefit other species in a
  community.
• 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?

• Frogs serve as indicator species because
  different parts of their life cycles can be
  easily disturbed.

Figure 8-3
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Adult frog(3 years)
Young frog
Sperm
Tadpole develops into frog
Sexual Reproduction
Tadpole
Eggs
Fertilized egg development
Egg hatches
Organ formation
Fig. 7-3, p. 147
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Case Study Why are Amphibians Vanishing?

• Habitat loss and fragmentation.
• Prolonged drought.
• Pollution.
• Increases in ultraviolet radiation.
• Parasites.
• Viral and Fungal diseases.
• Overhunting.
• Natural immigration or deliberate introduction of
  nonnative predators and competitors.

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Section 8-3

• Species Interactions
• Competition Predation
• Lion vs. Wildebeest

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Question of the Day

• Which of the following is the best example of a
  keystone species?
• Sea otter
• Sea urchin
• Spotted owl
• Snail darter
• E. Condor

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SPECIES INTERACTIONS COMPETITION AND PREDATION

• Species can interact through competition,
  predation, parasitism, mutualism, and
  commensalism.
• Some species have adaptations that allow them to
  reduce or avoid competition for resources with
  other species (resource partitioning).

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CompetitionResource Partitioning

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

Figure 7-7
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Competition Niche Specialization

• Niches become separated to avoid competition for
  resources
• Grizzlies Wolves

Figure 7-6
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PREDATION

• Species called predators feed on other species
  called prey.
• Organisms use their senses their senses to locate
  objects and prey and to attract pollinators and
  mates.
• Some predators are fast enough to catch their
  prey, some hide and lie in wait, and some inject
  chemicals to paralyze their prey.

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Prey adaptations

• 1. Some prey escape their predators
• Cheetah vs. Gazelle
• 2. Have outer protection
• 3. Some are camouflaged
• 4. Some use chemicals to repel predators.

Figure 7-8
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(a) Span worm
Fig. 7-8a, p. 153
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(b) Wandering leaf insect
Fig. 7-8b, p. 153
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(c) Bombardier beetle
Fig. 7-8c, p. 153
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(d) Foul-tasting monarch butterfly
Fig. 7-8d, p. 153
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(e) Poison dart frog
Fig. 7-8e, p. 153
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(f) Viceroy butterfly mimics monarch
butterfly
Fig. 7-8f, p. 153
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(g) Hind wings of Io moth resemble eyes of
a much larger animal.
Fig. 7-8g, p. 153
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(h) When touched, snake caterpillar changes
shape to look like head of snake.
Fig. 7-8h, p. 153
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Section 8-3

• Summary
• Competition
• Predation

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Section 8-4
SPECIES INTERACTIONS PARASITISM, MUTUALISM, AND
COMMENSALIM
Tongue Eaters
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Question of the Day

• Zero population growth is associated with
• Phase I only
• Phase II only
• Phase III only
• Phase IV only
• Phase I and IV

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PARASITISM, MUTUALISM, AND COMMENSALIM

• Parasitism occurs when one species feeds on part
  of another organism.
• In mutualism, two species interact in a way that
  benefits both.
• Commensalism is an interaction that benefits one
  species but has little, if any, effect on the
  other species.

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Parasites Sponging Off of Others

• Although parasites can harm their hosts, they can
  promote community biodiversity.
• 1. Some parasites live in host (micororganisms,
  tapeworms).
• Malaria
• 2. Some parasites live outside host (fleas,
  ticks, mistletoe plants, sea lampreys).
• 3. Some have little contact with host
  (dump-nesting birds like cowbirds, some duck
  species)

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Mutualism Win-Win Relationship

• Two species can interact in ways that benefit
  both of them.
• Unlikely Travel Companions

Figure 7-9
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(a) Oxpeckers and black rhinoceros
Fig. 7-9a, p. 154
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(b) Clownfish and sea anemone
Fig. 7-9b, p. 154
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(c) Mycorrhizal fungi on juniper seedlings in
normal soil
Fig. 7-9c, p. 154
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(d) Lack of mycorrhizal fungi on juniper
seedlings in sterilized soil
Fig. 7-9d, p. 154
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Commensalism Using without Harming

• 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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Section 8-4Summary

• Parasitism
• Mutualism
• Commensalism

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Section 8-5 8-6

• Ecological Succession
• Stability
• Essential Question
• How do communities undergo natural change?
• Mt St Helens

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Question of the Day

• Which of the following elements is most likely to
  limit primary production in freshwater lakes?
• A. Oxygen
• B. Calcium
• C. Phosphorus
• D. Carbon
• E. Iron

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COMMUNITIES IN TRANSITION

• New environmental conditions allow one group of
  species in a community to replace other groups.
• Ecological succession the gradual change in
  species composition of a given area
• Primary succession the gradual establishment of
  biotic communities in lifeless areas where there
  is no soil or sediment.
• Secondary succession series of communities
  develop in places containing soil or sediment.

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Primary Succession Starting from Scratch

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

Figure 7-11
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Typical Changes

• Community changes during succession include
  increases in species diversity and changes in
  species composition
• Characteristics of Pioneer Species
• Ecosystem changes during succession include
  increases in biomass, primary production,
  respiration, and nutrient retention.
• Modification of soil and other environmental
  changes lead to changes in species.

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Secondary Succession Starting Over with Some
Help

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

Figure 7-12
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Can We Predict the Path of Succession

• The course of succession cannot be precisely
  predicted.
• Previously thought that a stable climax community
  will always be achieved.
• Succession involves species competing for enough
  light, nutrients and space which will influence
  its trajectory.

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ECOLOGICAL STABILITY AND SUSTAINABILITY

• Living systems maintain some degree of stability
  through constant change in response to
  environmental conditions through
• Inertia (persistence) the ability of a living
  system to resist being disturbed or altered.
• Constancy the ability of a living system to keep
  its numbers within the limits imposed by
  available resources.
• Resilience the ability of a living system to
  bounce back and repair damage after (a not too
  drastic) disturbance.

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ECOLOGICAL STABILITY AND SUSTAINABILITY

• Having many different species appears to increase
  the sustainability of many communities.
• Human activities are disrupting ecosystem
  services that support and sustain all life and
  all economies.

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Chapter Overview Questions

• What determines the number of species in a
  community?
• How can we classify species according to their
  roles in a community?
• How do species interact with one another?
• How do communities respond to changes in
  environmental conditions?
• Does high species biodiversity increase the
  stability and sustainability of a community?