Community Theory

1. Community Theory Kenneth M. Klemow, Ph.D. Wilkes University

2. www.fws.gov/arizonaes “Pre-modern” community concept • Communities static entities • Composition depended on: • Climate • Temperature • Rainfall • Soils • Disturbance

3. 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

4. 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.

5. 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.

6. 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

7. Clementsian idea of species change along gradient

8. 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.

9. Gleasonsian idea of species change along gradient

10. www.nceas.ucsb.edu www.botany.org Evaluating Clements vs Gleason

11. 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.

12. Whittaker’s findings

13. Siskyou Mountains, Oregon Santa Catalina Mountains, Arizona. home.messiah.edu Whittaker’s findings

14. 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

15. Determining Coefficient of Community (CC) • CC =  min IV • Where min IV is lower Importance Value for each species

16. Generate matrix of CC values

17. Generate matrix of Dissimilarity Indices • DI = 100 - CC

18. Determine community pair with highest DI • These become endpoints of axis. C1 C3 20 40 60 80 100 0

19. 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

20. 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

21. Where would C2 go? C1 C4 C3 20 40 60 80 100 0

22. Where would C2 go? C2 60 40 C1 C4 C3 20 40 60 80 100 0

23. Where would C2 go? 60 40 C1 C2 C4 C3 20 40 60 80 100 0

24. IV 20 40 60 80 100 0 C3 C1 C2 C4 Now plot IV values for each species against community positions