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Community Theory. Kenneth M. Klemow, Ph.D. Wilkes University. www.fws.gov/arizonaes. “Pre-modern” community concept. Communities static entities Composition depended on: Climate Temperature Rainfall Soils Disturbance. Dynamic concept. Result of work by H. Cowles

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community theory

Community Theory

Kenneth M. Klemow, Ph.D.

Wilkes University

pre modern community concept

www.fws.gov/arizonaes

“Pre-modern” community concept
  • Communities static entities
  • Composition depended on:
    • Climate
      • Temperature
      • Rainfall
    • Soils
    • Disturbance
dynamic concept
Dynamic concept
  • Result of work by H. Cowles
  • Communities change over time
    • Parameters include
      • Species composition
      • Relative density
    • Due to internal processes

www.oceanservice.noaa.gov

clementsian community concept

www.nceas.ucsb.edu

www.tarleton.edu

Clementsian Community Concept
  • Introduced by Frederic Clements
  • Dominated ecological thinking in first 40 years of 20th Century
  • Key concepts
    • Association
    • Super-organismal analogy
    • Succession with seres, converging to monoclimax.
association

www.bigsurlandtrust.org

Association
  • Group of coevolved species.
  • Characteristic of climate
  • Extends for many square miles
  • Characteristic species composition
  • Can be classified
  • Equated to super-organism
  • Adjoining communities interface at ecotone.
succession

www.nescb.org

www.tarleton.edu

Succession
  • Deterministic, orderly change of species composition on a site.
  • Can be classified into
    • Primary
    • Secondary
  • Can be classified into
    • Hydrarch
    • Mesarch
    • Xerarch
  • Consists of a series of “seral” stages.
  • Relay floristics.
  • Converge to monoclimax characteristic of area.
  • Equated to ontogenetic development in organism
individualistic dissent

www.botany.org

Individualistic dissent
  • Proposed by Henry Gleason in 1920s and 1930s.
  • Communities not highly coevolved aggregations of species
  • Instead, chance assemblages of species having overlapping tolerances for prevailing environment.
  • Rejected deterministic, superorganismal analogy
  • Species change along gradients by blending continuum
  • Tight ecotones may occur when environmental change abrupt, but not necessarily true.
robert h whittaker

oz.plymouth.edu

Robert H. Whittaker
  • Ph.D University of Illinois.
  • Conducted analysis of woody plants
  • Computed importance values for each species
  • Related to obvious environmental gradient
    • Smoky Mountains, TN
    • Siskyou Mountains, Oregon
    • Santa Catalina Mountains, Arizona.
whittaker s findings13

Siskyou Mountains, Oregon

Santa Catalina Mountains, Arizona.

home.messiah.edu

Whittaker’s findings
what if an overriding gradient is not evident
What if an overriding gradient is not evident?
  • Perform an indirect gradient analysis through ordination or other statistical technique
  • Main steps:
    • Calculate Importance Values for each species in each community
    • Determine Coefficient of Community (CC) for each pair of communities
determining coefficient of community cc
Determining Coefficient of Community (CC)
  • CC =  min IV
    • Where min IV is lower Importance Value for each species
determine community pair with highest di
Determine community pair with highest DI
  • These become endpoints of axis.

C1

C3

20

40

60

80

100

0

place other communities at euclidean distance from reference
Place other communities at Euclidean distance from reference
  • C4 is 70 from C1, 50 from C3

C4

50

70

C1

C3

20

40

60

80

100

0

place other communities at euclidean distance from reference20
Place other communities at Euclidean distance from reference
  • C4 is 70 from C1, 50 from C3
  • Drop perpendicular

50

70

C1

C4

C3

20

40

60

80

100

0

where would c2 go
Where would C2 go?

C1

C4

C3

20

40

60

80

100

0

where would c2 go22
Where would C2 go?

C2

60

40

C1

C4

C3

20

40

60

80

100

0

where would c2 go23
Where would C2 go?

60

40

C1

C2

C4

C3

20

40

60

80

100

0