Gotelli & Graves: c. 7
The search for general mechanisms of community assembly remains a major focus in community ecology (Drake 1990, Samuels & Drake 1997). Diamond (1975) first suggested that communities on islands could be characterized by a set of "assembly rules" – deterministic patterns of distribution and abundance controlled by interspecific competition. Other investigators have extended and refined these assembly rules, hypothesizing preferred assemblages of species ("favored states" of Fox & Brown 1993) and relatively constant proportions of species sets defined empirically or statistically (Wilson & Roxburgh 1994, Wilson et al. 1995). Supporters of assembly rules argue that competition, in the form of resource preemption or competitive hierarchies, structures communities (e.g., Diamond 1975, Gilpin et al. 1986, Drake 1991). Critics of assembly rules assert that they are tautologies lacking predictive power (Connor & Simberloff 1979), or that evidence for consistent patterns of community structure, much less for assembly rules, is not compelling (Wiens 1980).
Chapter 7 of Gotelli & Graves (1996) provides a general overview of issues involved in, and methods for examining community assembly 'rules'. You should read this chapter and think about how you might look for assembly rules in one of your favorite natural communities. (Careful readers will observe that the preceding paragraph looks a lot like the second paragraph of chapter 7 in Gotelli & Graves [1996]. This is neither coincidence nor plagiarism. Nick Gotelli and I wrote the preceding paragraph in a grant proposal for studying assembly of insect communities associated with northern pitcher-plants that we submitted to the National Science Foundation. Nick used some of the prose from his own textbook to simplify the writing of this proposal).
The objective of this lab is for you to attempt to identify an "assembly rule" in a natural community that you find interesting. You should collect appropriate data (either from the field or from the published literature), organize it into a site x species matrix for analysis of assembly rules (see Gotelli & Graves, page 155 for an example), and statistically test it for non-randomness (see Gotelli & Graves, chapter 7 for methods). Based on your analytical results, discuss the organization of the community that you studied.
October 25: Choose a community to study, and develop appropriate sampling methodology. Note that collation of data from the literature is not as straight-forward as you probably imagine, and like field sampling, will require extensive thought regarding workable sampling methods.
November 1: Gather data, organize it, and begin to analyze it.
November 8: Finish data analysis; in-class discussion of preliminary results.
November 15: Write-up due.
You should write up the results from this lab in standard format, in no more than 10 pages. The introduction and discussion of your lab report should reflect your research into, and reading of, the primary ecological literature on assembly rules. Since this is a very active area of research, and since your instructor conducts his own research in this sub-field of ecology, you should be especially thorough in your literature review.
Be sure to clearly state your hypothesis in both the abstract and in the introduction. The methods should completely describe your sampling design. Your results should reflect careful analysis relevant to testing your hypothesis and they should be clearly and concisely presented. In your discussion, reflect on alternative explanations for your results. What experiments could be done to test these inferential explanations?
Connor, E. F. and D. Simberloff. 1979. The assembly of species communities: chance or competition? Ecology 60: 1132-1140.
Diamond, J. M. 1975. Assembly of species communities. Pages 342-444 In M. L. Cody and J. M. Diamond, editors. Ecology and evolution of communities. Harvard University Press, Cambridge.
Drake, J. A. 1990. Communities as assembled structures: do rules govern pattern? Trends in Ecology and Evolution 5: 159-164.
Drake, J. A. 1991. Community-assembly mechanics and the structure of an experimental species ensemble. The American Naturalist 137: 1-26.
Fox, B. J., and J. H. Brown. 1993. Assembly rules for functional groups in North American desert rodent communities. Oikos 67: 358-370.
Gilpin, M. E., M. P. Carpenter and M. J. Pomerantz. 1986. The assembly of a laboratory community: multi-species competition in Drosophila. Pages 33-40 in J. M. Diamond and T. J. Case, editors. Community ecology. Harper and Row, New York.
Samuels, C. L. and J. A. Drake. 1997. Divergent perspectives on community convergence. Trends in Ecology and Evolution 12: 427-432.
Wiens, J. A. 1980. Concluding comments: are bird communities real? Acta XVII Congressus Internationalis Ornithologici 1088-1089.
Wilson, J. B. and S. H. Roxburgh. 1994. A demonstration of guild-based assembly rules for a plant community, and determination of intrinsic guilds. Oikos 69: 267-276.
Wilson, J. B., R. B. Allen, and W. G. Lee. 1995. An assembly rule in the ground and herbaceous strata of a New Zealand rain forest. Functional Ecology 9: 61-64.