1. Communities

2. General Approaches to the Study of Plant Communities
Classification
 taxonomy

3. Classification: the “Association” as an example
 taxonomy
Artemesia tridentata-Agropyron
Agropyron - Festuca

4. Required characteristics
What is an Association?
Required characteristics
Consistent floristic composition
Uniform physiognomy
Occurs in a particular habitat (i.e., determined by environment)

5. Consistent floristic composition

6. Consistent floristic composition
What types of species are useful in classification?
Extremely common?
No – not habitat specific enough
Rare?
No – not reliable
Moderately common?
Perhaps, if exhibit high habitat fidelity

7. Required characteristics
What is an Association?
Required characteristics
Consistent floristic composition
Uniform physiognomy
Occurs in a particular habitat (i.e., determined by environment)

8. Form, structure or appearance of a plant community
Physiognomy
Form, structure or appearance of a plant community

9. Physiognomy

10. Physiognomy

11. Required characteristics
What is an Association?
Required characteristics
Consistent floristic composition
Uniform physiognomy
Occurs in a particular habitat (i.e., determined by environment)

12. Habitat Specificity
Classification
 taxonomy

13. Utility of the Taxonomic Approach
Can categorize or name “communities”
Useful for mapping
Ecologically meaningful?

14. General Approaches to the Study of Plant Communities
Classification
 taxonomy
Comparison
Convergent evolution under similar environments

15. Kalahari of South Africa
Convergent evolution
Monument Valley, U.S.A
Kalahari of South Africa

16. General Approaches to the Study of Plant Communities
Classification
 taxonomy
Comparison
Convergence in community structure under similar environmental conditions
Comparison of communities under locally varying environmental conditions
Patterns of diversity

17. General Approaches to the Study of Plant Communities
Classification
 taxonomy
Comparison
Process level studies
Succession
Response to disturbance
Assembly rules

18. Are Plant Communities Real? An historically important debate

19. Organismic vs. Individualistic Viewpoints

20. The Organismic Viewpoint of Clements
Plants are highly coadapted to their environments
+/+ and 0/0 interactions predominate
Long mutual history of organisms
Sum > Parts
Emergent properties
Community as superorganism
Species:Community :: Tissues:Organism

21. Predictions of the Organismic Viewpoint
Parallel distribution patterns along gradients
Narrow ecotones

22. The Individualistic Viewpoint of Gleason
Species are distributed according to individual characteristics
-/- interactions predominate
Community is not an integrated organism
No emergent properties
Communities are an artificial construct of convenience

23. Predictions of the Individualistic Viewpoint
Independent distributions along gradients
Few discernable ecotones

24. An approach developed by Curtis and Whittaker
Resolving the Debate
An approach developed by Curtis and Whittaker

25. Studies of species distributions relative to environmental gradients
(1) Sample sites for criticial environmental conditions and species composition
(2) Arrange data in a plot:
Species a
species along an ordered gradient
Abundance
Moisture

26. The Evidence
Tree species along a moisture gradient in Wisconsin (Curtis)

27. The Evidence
Plant species with altitude in the Great Smoky Mountains (Whittaker)

28. The Evidence
Plant species with altitude in the Great Smoky Mountains (Whittaker)

29. The Bottom Line
The individualistic hypothesis is a more appropriate characterization of ecological reality

30. Community Characterization
What do we measure?

31. Species Richness: a first step
Richness: the number of species in the community

32. Species Richness
How do we sample?

33. Sampling Schemes: The Line Transect

34. Sampling Schemes: The Quadrat

35. Sampling Schemes: The Band Transect

36. Species Richness: How much area do we sample?

37. Species Area Curves

38. Species Area Curves

39. Species Area Curves
Rapid initial increase as encounter very common and moderately common species

40. Species Area Curves
Slower rate of increase as most species already encountered; sporadically find rare or uncommon species

41. Estimating Total Species Number
Smax

42. Examples from the Tropics
Smax?

43. Problems in Estimating Smax
Can’t find all rare species
As area sampled increases different “habitats” are encountered
Too much effort required to find less common species

44. Minimal Area Estimates