Species Interactions and Community Ecology

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Species Interactions and Community Ecology

• Chapter 6

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Species interactions

• Species interact in several fundamental ways.

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Species interactions

• When multiple species seek the same limited
  resource
• Interspecific competition is between two or
  more species.
• Intraspecific competition is within a species.
• Usually does not involve active fighting, but
  subtle contests to procure resources.

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Interspecific competition

• Different outcomes
• Competitive exclusion one species excludes the
  other from a resource
• Species coexistence both species coexist at a
  ratio of population sizes, or stable equilibrium

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Niche

• Coexisting competitors may adjust their resource
  use, habitat use, or way of life to minimize
  conflict.

Fundamental niche
Realized niche
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Interspecific competition

• Adjusting resource use, habitat use, or way of
  life over evolutionary time leads to
• Resource partitioning species specialize in
  different ways of exploiting a resource
• Character displacement physical characters
  evolve to become different to better
  differentiate resource use

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Resource partitioning

• Tree-climbing bird species exploit insect
  resources in different ways.

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Predation

• One species, the predator, hunts, kills, and
  consumes the other, its prey.

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Predatorprey cycles

• Population dynamics of predatorprey systems
  sometimes show paired cycles ups and downs in
  one, drive ups and downs in the other.

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Predation drives adaptations in prey
Mimicry Fool predators (here, caterpillar mimics
snake)
Cryptic coloration Camouflage to hide from
predators
Warning coloration Bright colors warn that prey
is toxic
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Parasitism

• One species, the parasite, exploits the other
  species, the host, gaining benefits and doing
  harm.

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Herbivory

• One of the most common types of exploitation is
  herbivory, which occurs when animals feed on the
  tissues of plants.

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Mutualism

• Both species benefit one another.
• Hummingbird pollinates flower while gaining
  nectar for itself.

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Amensalism and commensalism

• Amensalism one species is harmed the other is
  unaffected
• Commensalism one species benefits the other is
  unaffected

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Roles in communities

• By eating different foods, organisms are at
  different trophic levels, and play different
  roles in the community.
• Plants and other photosynthetic organisms are
  producers.

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Consumers

• Animals that eat plants are primary consumers, or
  herbivores.
• Animals that eat herbivores are secondary
  consumers.
• Detritivores and decomposers eat nonliving
  organic matter they recycle nutrients.

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Trophic levels

• Together, these comprise trophic levels

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Food chains and webs
We can represent feeding interactions (and thus
energy transfer) in a community

• Food chain simplified linear diagram of who
  eats whom
• Food web complex network of who eats whom

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Food web for an eastern deciduous forest
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Keystone species

• Species that have especially great impacts on
  other community members and on the communitys
  identity
• If keystone species are removed, communities
  change greatly.

A keystone holds an arch together.
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Keystone species

• When the keystone sea otter is removed, sea
  urchins overgraze kelp and destroy the kelp
  forest community.

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Resistance and resilience

• A community that remains stable despite
  disturbance is showing resistance to the
  disturbance.
• A community shows resilience when it changes in
  response to disturbance but later returns to its
  original state.

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Succession

• A series of regular, predictable, quantifiable
  changes through which communities go
• Primary succession Pioneer species colonize a
  newly exposed area (lava flows, glacial retreat,
  dried lake bed).
• Secondary succession The community changes
  following a disturbance (fire, hurricane,
  logging).

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Secondary terrestrial succession
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Primary aquatic succession

• 1. Open pond
• 2. Plants begin to cover surface sediment
  deposited
• 3. Pond filled by sediment vegetation grows over
  site

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Climax Community

• The transitions between stages of succession
  eventually lead to a climax community.
• The climax community remains in place, with
  little modification, until some disturbance
  restarts succession.

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Clements vs. Gleason

• Frederick Clements believed that communities are
  cohesive entities whose members remain associated
  over time and space.
• Henry Gleason maintained that communities are not
  cohesive units, but temporary associations of
  individual species that can reassemble into
  different combinations.

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Temperate deciduous forest

• Temperature moderate, seasonally variable
• Precipitation stable through year
• Trees deciduous lose leaves in fall, dormant in
  winter
• Moderate diversity of broad-leafed trees
• North America, Europe, China

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Temperate grassland

• Temperature moderate, seasonally variable
• Precipitation sparse but stable
• Grasses dominate few trees
• Large grazing mammals
• North America, Asia, South America

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Temperate rainforest

• Temperature moderate
• Precipitation very high
• Trees grow tall
• Dark moist forest interior
• Pacific northwest region of North America, Japan

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Tropical rainforest

• Temperature warm, seasonally stable
• Precipitation high
• Trees tall forest interior moist and dark
• Extremely high biodiversity
• Soil poor in organic matter is aboveground
• Equatorial regions

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Tropical dry forest

• Temperature warm, seasonally stable
• Precipitation highly seasonally, variable
• Trees deciduous dormant in dry season
• High biodiversity
• Subtropical latitudes

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Savanna

• Temperature warm
• Precipitation highly seasonal, variable
• Grassland interspersed with trees
• Large grazing mammals
• Africa and other dry tropical regions

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Desert

• Temperature warm in most, but always highly
  variable b/w day and night
• Precipitation extremely low
• Vegetation sparse growth depends on periods of
  rain
• Organisms adapted to harsh conditions
• Southwestern region of North America, Australia,
  Africa

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Tundra

• Temperature cold, seasonally variable
• Precipitation very low
• Vegetation very low and sparse no trees
• Low biodiversity high summer productivity
• Arctic regions

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Boreal forest

• Temperature cool, seasonally variable
• Precipitation low to moderate
• Coniferous (evergreen) trees dominate monotypic
  forests
• Low biodiversity high summer productivity
• Subarctic regions

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Chaparral

• Temperature seasonally variable
• Precipitation seasonally variable
• Evergreen shrubs dominate
• Plants resistant to fire burns frequently
• California, Chile, West Australia

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Altitude creates patterns

• As altitude increases, vegetation changes in ways
  analogous to changes in latitude.

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Conclusion

• Dividing the worlds communities into major
  types, or biomes, is broadly informative.
• Understanding how communities function at local
  scales requires understanding species
  interactions.
• Types of species interactions include predation,
  parasitism, competition, and mutualism.

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Conclusion

• Feeding relationships are represented by trophic
  levels and food webs, and influential species are
  called keystone species.
• Humans alter communities by introducing
  non-native species that may turn invasive.
• Ecological restoration can undo the changes we
  have caused.

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QUESTION Review
Which of the following lists of trophic levels is
in the correct order?

• a. Producer, secondary consumer, herbivore
• b. Producer, herbivore, secondary consumer
• c. Secondary consumer, producer, detritivore
• d. Herbivore, carnivore, producer

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QUESTION Review
Primary succession would take place on all of the
following EXCEPT?

• a. The slopes of a Hawaiian volcanos new lava
  flow
• b. A South Carolina coastal forest after a
  hurricane
• c. Alaskan land just uncovered as a glacier
  melts
• d. A new island formed by falling levels of a
  reservoir in Ohio

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QUESTION Review
Which biome has warm stable temperatures, highly
seasonal rainfall, deciduous trees, and high
biodiversity?

• a. Tropical rainforest
• b. Tropical dry forest
• c. Temperate rainforest
• d. Taiga

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Question Weighing the Issues
What would you recommend as the primary approach
to dealing with invasive species in a bay area
with heavy maritime trade, and why?

• a. Establish tough restrictions with trading
  partners
• b. Use chemical treatments, barriers, and
  removal
• c. Use biological control
• d. Some combination of the above (describe)

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QUESTION Interpreting Graphs and Data

• What does the graph illustrate?
• a. Paired predatorprey cycle
• b. Competitor exclusion
• c. Resource partitioning
• d. Succession

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QUESTION Interpreting Graphs and Data

• In this climatograph for Los Angeles, California,
  in the chaparral biome, summers are ?
• a. Warm and dry
• b. Warm and wet
• c. Mild and dry
• d. Mild and wet

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QUESTION Viewpoints

• A celebrity made headlines when she illegally
  brought an apple into the U.S. from abroad. How
  far should governments go to prevent invasive
  species?
• a. As far as they can preventing invasive
  species is worth the expense and inconvenience of
  strict regulations.
• b. Governments need to be reasonable in allowing
  for important activities (e.g., ship movement).
• c. The threat of invasive species is vastly
  overrated, and governments should focus on more
  important priorities.