1. Community Assembly Rules

2. Outline Defining “assembly rules” The niche concept
Types of assembly rules
Obstacles to testing assembly rules
So what?

3. Outline Defining “assembly rules” The niche concept
Types of assembly rules
Obstacles to testing assembly rules
So what?

4. Defining “assembly rules”
“Ecological restrictions on the observed patterns of species presence or abundance that are based on the presence or abundance of one or more other species or groups of species (not simply the response of individual species to the environment).”
Wilson & Gitay 1995
Rules based on species co-occurences/interactions NOT on species responses to environmental variation--can determine diversity and composition

5. Defining “assembly rules”
Rules based on species co-occurences/interactions NOT on species responses to environmental variation--can determine diversity and composition
Zobel 1997
How communities are assembled out of pools after passing through abiotic environmental filters.

6. Outline Defining “assembly rules” The niche concept
Types of assembly rules
Obstacles to testing assembly rules
So what?

7. The niche concept
“No concept in ecology has been more variously defined or more universally confused than the ‘niche.’
Real & Levin 1991

8. The niche concept
“No concept in ecology has been more variously defined or more universally confused than the ‘niche.’
Real & Levin 1991
Origins of niche theory
-Grinnell 1917 (habitat)
-Elton 1927 (biological function)
-Gause 1934 (competitive exclusion)
-Hutchinson 1957 (fundamental and realized)

9. The niche concept
“No concept in ecology has been more variously defined or more universally confused than the ‘niche.’
Real & Levin 1991
Origins of niche theory
One definition
A species’ fundamental niche is defined by the combination of conditions and resources which allow the species to maintain a viable population. Its realized niche is defined by the conditions and resources utilized by the species in the presence of (negative) interspecific interactions.

10. The niche concept
“No concept in ecology has been more variously defined or more universally confused than the ‘niche.’
Real & Levin 1991
Origins of niche theory
One definition
Niche theory and community assembly
-Limiting similarity

11. Limiting similarity: “There is a limit to the similarity (and hence to the number) of competing species which can coexist.” MacArthur and Levins 1967
Limiting similarity
esource gradient
MacArthur and Levins 1967

12. Outline Defining “assembly rules” The niche concept
Types of assembly rules
Obstacles to testing assembly rules
So what?

13. Types of assembly rules
Rules based on particular species
Diamond 1975
Connor and Simberloff 1979 (reply)
After Wilson 1999

14. Types of assembly rules
Rules based on particular species
Rules based on presence/absence
-variance in richness
-local vs. regional richness
Cornell and Lawton 1992
-large-scale distributions
After Wilson 1999

15. Types of assembly rules
Rules based on particular species
Rules based on presence/absence
Rules based on species’ characters
-texture convergence
Watkins and Wilson 2003
-limiting similarity
Watkins and Wilson 1992, Kelt and Brown 1999
-guild/functional group based
Fox and Brown 1993, Wilson and Roxburgh 1994, Fox 1999
After Wilson 1999

16. Types of assembly rules
Rules based on particular species
Rules based on presence/absence
Rules based on species’ characters
-intrinsic guilds
Wilson and Roxburgh 1994, Cody 1999
After Wilson 1999

17. Types of assembly rules
Rules based on particular species
Rules based on presence/absence
Rules based on species’ characters
Rules based on species abundance
-biomass constancy
-abundance-based guild proportionality
-Relative Abundance Distributions (RAD)
After Wilson 1999

18. Outline Defining “assembly rules” The niche concept
Types of assembly rules
Obstacles to testing assembly rules
So what?

19. Obstacles to testing assembly rules
Appropriate null models
Narcissus effect-Type II error
I.e. “sampling from a post-competition pool underestimates the role of competition, since its effect is already reflected in the pool.” Colwell and Winkler 1984
Jack Horner effect-Type I error
I.e. “demonstration of the obvious” [e.g. some sites are richer than others, some species have larger ranges than others], “from failure to build into the null model features one does not want to be told about.” Wilson 1995

20. Obstacles to testing assembly rules
Appropriate null models
Environmental heterogeneity (different spp. in different environments)
Spatial autocorrelation (non-independence)

21. Outline Defining “assembly rules” The niche concept
Types of assembly rules
Obstacles to testing assembly rules
So what?

22. So what? Invasibility Community dis-assembly
Does limiting similarity exist?
Do local processes constrain richness?

23. Do assembly rules exist?
How important are they?

26. Why are more diverse communities more resistant to invasion?
communities should
have less space
available
native species abundance
total unoccupied space .
1 - Species system
2 - Species system
Percent cover
3 - Species system
Time
Time