Transcript Community Theory - Wilkes University

Community Theory
Kenneth M. Klemow, Ph.D.
Wilkes University
“Pre-modern” community
concept
 Communities static entities
 Composition depended on:
 Climate
 Temperature
 Rainfall
 Soils
 Disturbance
www.fws.gov/arizonaes
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
 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.
www.nceas.ucsb.edu
www.tarleton.edu
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.
www.bigsurlandtrust.org
Succession
 Deterministic, orderly change of species
composition on a site.
 Can be classified into
 Primary
 Secondary
www.nescb.org
 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
www.tarleton.edu
Clementsian idea of species
change along gradient
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.
www.botany.org
Gleasonsian idea of species
change along gradient
Evaluating Clements vs Gleason
www.nceas.ucsb.edu
www.botany.org
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.
oz.plymouth.edu
Whittaker’s findings
Whittaker’s findings
Siskyou Mountains, Oregon
Santa Catalina Mountains, Arizona.
home.messiah.edu
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)
 CC =  min IV
 Where min IV is lower
Importance Value for each
species
Sp.
C1
C2
CC
A
30
20
20
B
10
30
10
C
20
0
0
D
40
10
10
E
0
40
0
100 100
40
Tot.
Generate matrix of CC values
C1
C2
C3
C4
C1
100
C2
40
100
C3
10
60
100
C4
30
30
50
100
Generate matrix of Dissimilarity
Indices
 DI = 100 - CC
C1
C2
C3
C4
C1
C2
C3
C1 100
C1
0
C2
40 100
C2
60
0
C3
10
60 100
C3
90
40
0
C4
30
30
C4
70
70
50
50 100
C4
0
Determine community pair with
highest DI
 These become endpoints of axis.
C1
C2
C3
C1
0
C2
60
0
C3
90
40
0
C4
70
70
50
C4
0
C1
0
C3
20
40
60
80
100
Place other communities at
Euclidean distance from reference
 C4 is 70 from C1, 50 from C3
C1
C1
0
C2
60
C2
C3
C4
C4
0
C3
90
40
0
C4
70
70
50
50
70
C1
C3
0
0
20
40
60
80
100
Place other communities at
Euclidean distance from reference
 C4 is 70 from C1, 50 from C3
 Drop perpendicular
C1
C1
0
C2
60
C2
C3
C4
0
C3
90
40
0
C4
70
70
50
50
70
C1
C4
C3
0
0
20
40
60
80
100
Where would C2 go?
C1
C2
C3
C1
0
C2
60
0
C3
90
40
0
C4
70
70
50
C4
C1
C4
C3
0
0
20
40
60
80
100
Where would C2 go?
C1
C2
C3
C1
0
C2
60
0
C3
90
40
0
C4
70
70
50
C4
C2
60
40
C1
C4
C3
0
0
20
40
60
80
100
Where would C2 go?
C1
C2
C3
C1
0
C2
60
0
C3
90
40
0
C4
70
70
50
C4
60
40
C1
C2 C4
C3
0
0
20
40
60
80
100
Now plot IV values for each species
against community positions
IV
0
C1
20
40
60
C2
C4
80
C3
100