Community Ecology 1

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Community Ecology 1
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Frederick Clements
Organismic View Association-unit view
A Community is like an organismthat develops
through timeinto an integrated,
self-regulatingentity.
Expectation repeated, identifiable community
types with distinct boundaries stability
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Henry Gleason Individualistic Concept a
community is merely the coincidental
co-occurrence of species that happen to be able
to live in a particular spot Expectation no
clear boundaries between communities community
membership is unstable in time
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• Gradient
• continuous variation in environment (e.g. soil
  quality, elevation, moisture) non-contiguous
  variation rearranged or depicted as if it were
  contiguous

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Soil catena

• Multiple factors covarying(soil particle size,
  nutrient content, organic matter, moisture,
  possibly fire or disturbance frequency)

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Non-contiguous gradient
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Robert Whittaker
Transformed individualistic view into direct
gradient analysis. Pioneered diversity,
dominancepattern analysis.Started as
zoologist, decided to study plants as prelim. to
bugs. Was refused tenure because his ideas were
controversial
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The continuum concept

• Communities change gradually
• most species have their own unique requirements
  and preferences
• while a community / an organism, species are not
  independent either

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Species pool
Abiotic Gate filter Required Adaptations Individua
listic View
Com.
Biotic Filter Interactions/Coexistence
Com.
Community subset of species pool
"Niche-Assembly Theory"
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CONTEXT
COMMUNITY
HISTORY
RESOURCES
PROCESSES
INTER- ACTIONS
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Niche - role ... guild Fundamental Niche the set
of resources and conditions under which a species
can survive and reproduce Realized Niche the
set of resources and conditions under which a
species is observed to survive and reproduce
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http//www.tiehh.ttu.edu/scox/niche.html/niche_map
.html
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Kinds of Interactions

recipient
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donor
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what causes this pattern?
Chthalamus
Semibalanus
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Exploitation Competition -- using up a limiting
resource Interference Competition -- directly
reducing the ability to acquiring resources
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competitive exclusion principle"no 2 species
can occupy the same niche indefinitely when
resources are limiting"
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Liebig's Law of the Minimum the resource lowest
in abundance relative to its need will be
limiting
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Resource Partitioning Limiting Similarity
http//www.usd.edu/biol/faculty/swanson/ornith/pic
s/MacArthur's2020Warblers.gif
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Resource Partitioning Limiting Similarity
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Character Displacement
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demonstration science -- detecting interspecific
competition
note experimental design
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predators reduce competition
... keystone species concept
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Competition may be affected by mutualists?
Above-ground and Below-ground Competition
Intensity Andropogon gerardii Heliopsis
helianthoides
with neighbors
without neighbors
with neighbor roots only
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Direct vs. indirect interactions
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Community Ecology 2 Dynamics
http//www.cosmos.ne.jp/breach/act-photo/predate/
predator1-2.jpeg
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Food Chain
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Food Web
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Energy Flow through a Food Chain
1000
150
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1.2
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80-90 loss of Energy per trophic level
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pyramid of biomass
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Top-down vs. bottom-up controls on
production issues efficiency,
omnivory top-down control bottom-up control
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Primary Succession
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Secondary Succession
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• Mechanisms of Succession
• Facilitation by early species
• Inhibition of early species
• Tolerance by all, earlies just arrive first

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