Community Ecology
Community assembly and null models
Outline:
1. Definition of community assembly
2. Effects of scale (local and regional)
3. Diamond’s assembly rules, derived from checkerboard patterns of species’ incidences on
islands
A. Mechanism: competition, resulting in permissible and forbidden combinations
4. Connor and Simberloff’s criticism of Diamond
A. Null models
B. Let the war begin!
5. Nestedness
6. Final comments
Terms/people:
Assembly (cf. succession)
Checkerboard pattern
Null model
High-S species
Cole
assembly rules
Jared Diamond
permissible and forbidden species combinations
Dan Simberloff
nestedness
supertramps
companions in starvation
species incidence function
deletion rules
community assembly
cf. succession
Is community assembly predictable? (Reminiscent of Clements/Gleason argument.) If so, there
should be assembly rules:
Jared Diamond 1975 - birds of New Guinea and its satellite islands
“checkerboard pattern” of species co-occurrence with “permissible” and “forbidden”
species combos based on life history traits and competition
6 types of species combos: “high-S” species  A-D tramps  “suptertramps”
tradeoff between dispersal and competitive ability (for more info, read Cadotte et al.
2006)
species incidence functions
Connor and Simberloff 1979, 1984, 1986 - criticized Diamond’s use of competition to explain
community patterns (and his tacit assumption of equilibrium)
null model
Diamond’s (1975) assembly rules for communities:
a. If one considers all the combinations that can be formed from a group of related species, only
certain ones of these combinations exist in nature.
b. Permissible combinations resist invaders that would transform them into forbidden
combinations.
c. A combination that is stable on a large or species-rich island may be unstable on a small or
species-poor island.
d. On a small or species-poor island, a combination may resist invaders that would be
incorporated on a larger or more species-rich island.
e. Some pairs of species never coexist, either by themselves or as part of a larger combination.
f. Some pairs of species that form an unstable combination by themselves may form part of a
stable larger combination.
g. Conversely, some combinations that are composed entirely of stable subcombinations are
themselves unstable.
Connor and Simberloff’s (1979) criticisms of these rules:
Re: Rule c: Basically a statement that species-rich islands contain more combinations than
species- poor islands, which seem inevitable. Therefore, Rule c is trivial.
Re: Rule b: The evidence for “resistance” is weak; rule then states only that permissible
combinations occur and forbidden combinations do not. Therefore, Rule b is a tautology.
Re: Rule d: A combination of Rules b and c; therefore, Rule d is a trivial tautology.
Re: Rule f: Because there are no islands that contain just a pair of species, pairs cannot occur by
themselves. Therefore, Rule f is untestable.
Re: Rules a, e, and g: Use null model analysis to show that “there is nothing about the absence of
certain species pairs or trios...that would not be expected were the birds not randomly distributed
over the islands...Since there are so many possible sets of species, it is to be expected that a few
sets are not found on any island; this does not imply that such sets are actively forbidden by any
deterministic forces.”
Degenerated into a fierce debate. What emerged (to the benefit of ecology as a whole) was an
appreciation of a benchmark for comparison, a null model. As in statistics, where a null model
is used to provide a standard of comparison, an ecological null model provides a way of
distinguishing true pattern from randomness (Gotelli and Graves 1996). Something to think
about: a truly random assemblage (true null model) is biologically unrealistic  so why use
null models?
"face in the tortilla" analogy
Cole 1983 - mangrove ant communities invasion/removal experiments
Found that dispersal capabilities and chance (à la null model) may determine who gets to
an island first, but once established, could repel other species from competition (à la Diamond).
Nested community structure & predictability
Bottom line: The process of community assembly begins with a species pool, from which some
species are able to colonize a local area; of these, some species become established to form the
community. But because this process is a continuing one and local extinctions occur, community
composition is dynamic rather than fixed.
Next lecture: priority effects and the lottery hypothesis of community assembly
References:
Abbott, I. 1980. Theories dealing with the ecology of landbirds on islands. Advances in
Ecological Research 11:329-371.
Alatalo, R.V. 1982. Bird species distributions in the Galapagos and other archipelagoes:
competition or chance? Ecology 63:881-887.
Anderson, G.R.V., A.H. Ehrlich, P.R. Ehrlich, J.D. Roughgarden, B.C. Russell, and F.H. Talbot.
1981. The community structure of coral reef fishes. Am. Nat. 117:476-495.
Cadotte, M.W., D.V. Mai, S. Jantz, M.D. Collins, M. Keele and J.A. Drake. 2006. On testing
the competition-colonization tradeoff in a multispecies assemblage. Am. Nat. 168:704-709.
Cole, B.J. 1983. Assembly of mangrove ant communities: patterns of geographical distribution.
J. Anim. Ecol. 52:339-347.
Cole, B.J. 1983. Assembly of mangrove ant communities: colonization abilities. J. Anim. Ecol.
52:349-355.
Colwell, R.K., and D.W. Winkler. 1984. A null model for null models in biogeography. Pp. 344359 in: Ecological Communities: Conceptual Issues and the Evidence (D.R. Strong, Jr., D.
Simberloff, L.G. Abele, and A.B. Thistle, eds.). Princeton University Press, Princeton, NJ.
Connor, E.F., and D. Simberloff. 1979. The assembly of species communities: chance or
competition? Ecology 60:1132-1140.
Connor, E.F., and D. Simberloff. 1984. Neutral models of species’ co-occurrence patterns. Pp.
316-331 in: Ecological Communities: Conceptual Issues and the Evidence (D.R. Strong, Jr., D.
Simberloff, L.G. Abele, and A.B. Thistle, eds.). Princeton University Press, Princeton, NJ.
Connor, E.F., and D. Simberloff. 1986. Competition, scientific method, and null models in
ecology. Amer. Sci. 74:155-162.
Diamond, J.M. 1975. Assembly of species communities. Pp. 342-444 in: Ecology and Evolution
of Communities (M.L. Cody and J.M. Diamond, eds.). Belknap Press, Cambridge, MA.
Diamond, J.M. 1982. Effects of species pool size on species occurrence frequencies: musical
chairs on islands. Proc. Natl. Acad. Sci. USA 52:2420-2424.
Diamond, J.M., and M.E. Gilpin. 1982. Examination of the “null” model of Connor and
Simberloff for species co-occurrences on islands. Oecologia 52:64-74. Drake, J.A. 1990.
Communities as assembled structures: do rules govern patterns? Trends Ecol. Evol. 5:159-164.
Drake, J.A., T.E. Flum, G.J. Witteman, T. Voskuil, A.M. Hoylman, C. Creson, D.A. Kenny,
G.R. Huxel, C.S. Larue, and J.R. Duncan. 1993. The construction and assembly of an ecological
landscape. J. Anim. Ecol. 62:117-130.
Fernández-Juricic, E. 2002. Can human disturbance promote nestedness? A case study with
breeding birds in urban habitat fragments. Oecologia 131:269-278.
Gilpin, M.E., M.P. Carpenter, and M.J. Pomerantz. 1986. The assembly of a laboratory
community: multispecies competition in Drosophila. Pp. 23-40 in: Community Ecology (J.
Diamond and T.J. Case, eds.). Harper & Row, New York, NY.
Gilpin, M.E., and J.M. Diamond. 1982. Factors contributing to non-randomness in species cooccurrences on islands. Oecologia 52:75-84.
Gilpin, M.E., and J.M. Diamond. 1984. Are species co-occurrences on islands non-random, and
are null hypotheses useful in community ecology? Pp. 297-315 in: Ecological Communities:
Conceptual Issues and the Evidence (D.R. Strong, Jr., D. Simberloff, L.G. Abele, and A.B.
Thistle, eds.). Princeton University Press, Princeton, NJ.
Gotelli, N.J., and A.M. Ellison. 2002. Assembly rules for New England ant assemblages. Oikos
99:591-599.
Gotelli, N.J., and D.J. McCabe. 2002. Species co-occurrence: a meta-analysis of J.M.
Diamond’s assembly rules model. Ecology 83:2091-2096.
Gotelli, N.J., and G.R. Graves. 1996. Null Models in Ecology. Smithsonian Institution Press,
Washington, D.C.
Haefner, J.W. 1988. Assembly rules for Greater Antillean Anolis lizards: competition and
random models compared. Oecologia 74:551-565.
Harvey, P.H., R.K. Colwell, J.V. Silvertown, and R.M. May. 1983. Null models in ecology. Ann.
Rev. Ecol. Syst. 14:189-211.
Keddy, P.A. 1992. Assembly and response rules: two goals for predictive community ecology. J.
Veg. Sci. 3:157-164.
Mac Nally, R., G. Horrocks, and A.F. Bennett. 2002. Nestedness in fragmented landscapes:
birds of the box-ironbark forests of south-eastern Australia. Ecography 25:651-660.
Roughgarden, J. 1989. The structure and assembly of communities. Pp. 203-226 in: Perspectives
in Ecological Theory (J. Roughgarden, R.M. May, and S.A. Levin, eds.). Princeton University
Press, Princeton, NJ.
Simberloff, D. 1984. Properties of coexisting bird species in two archipelagoes. Pp. 234-253 in:
Ecological Communities: Conceptual Issues and the Evidence (D.R. Strong, Jr., D. Simberloff,
L.G. Abele, and A.B. Thistle, eds.). Princeton University Press, Princeton, NJ.
Weiher, E., and P. Keddy, eds. 1999. Ecological Assembly Rules: Perspectives, Advances,
Retreats. Cambridge University Press, Cambridge, UK.