Community Ecology
Competition: experiments
Outline:
1. Experiments on competition
A. de Wit replacement series (substitutive experiment)
i. Marshall and Jain’s field experiments on oats
B. Buchanan et al.’s additive experiment
2. Results from some other classic experiments on competition
A. Park and lab experiments on flour beetles
B. Connell and field experiments on barnacles
C. Abramski et al. field experiments on gerbils
3. Competition as the main force driving species co-occurrences?
A. 3 classic reviews: Schoener, Connell, Goldberg & Barton
B. Gurevitch et al.’s meta-analysis
C. David Tilman's review of plant competition studies
D. John Wiens’ criticisms of competition studies
4. Conclusions on competition
Terms/people:
meta-analysis (Gurevitch et al.)
additive experiment (Buchanan et al.)
“ecological crunches” (Wiens)
Abramski et al.
replacement series (de Wit, Marshall & Jain)
substitutive experiment
Thomas Park
J. Connell
Experiments provide stronger evidence for competition than can theoretical or descriptive
studies. Be sure you can explain why this is so.
How to tell if competition is present:
Must prove that resource is shared and limited (harder to do than it sounds; most studies just
assume resource is limited but do not measure it) by:
1) manipulating resources
2) manipulating number of competitors - e.g. C.T. de Wit’s replacement series/substitutive
experiments or by additive experiments (see Fig. 8.9 in Mittelbach text for a comparison of
these (and other) experimental designs used to study competition)
Some other important experiments on competition:
Thos. Park 1948, 1954, 1962 – flour beetles: Tribolium confusum and T. castaneum 
outcome of competition affected by environment
J. Connell 1961 - Scottish barnacles: Chthamalus stellatus and Balanus balanoides
Abramski et al. 1991 - “activity density” of gerbils in the Negev Desert of Israel:
Gerbillus allenbyi and G. pyramidum
From these experiments, is competition typically symmetrical?
Competition has been considered to be the most powerful force driving species cooccurrences (i.e., community structure). But does it really play that role?
Reviews of the incidence of interspecific competition in field experiments:
T. Schoener (1983)
J. Connell (1983)
Goldberg and Barton (1992)
Publication bias?
Gurevitch et al. (1992) - performed a meta-analysis to quantify competition from experiments
D. Tilman (1989) - review
50% were at a spatial scale < 1m
75% were at a spatial scale < 10 x 10 m
85% lasted < 3 years
J.A. Wiens’ (1977) criticisms of competition studies
competition important only during "ecological crunches"?
Summary of competition in community ecology:
In interspecific competition, individuals of one species suffer a reduction in health, fitness, or
survivorship as a result of resource exploitation or interference from individuals of another
species. The competitive exclusion principle dictates that competing species cannot persist
unless the species undergo niche partitioning: coexistence is possible if the species utilize
resources in different ways. Niche differentiation results in character displacement to ease
competition pressures because there is a limit to how similar competing species can be and still
coexist (limiting similarity). Coexistence is also possible in a heterogeneous environment
(which explains the paradox of the plankton). Mathematical models (most notably the LotkaVolterra model) have led to a more quantitative understanding of factors that influence
competition, but the simplified assumptions behind these models limit their applicability to real
communities–experiments provide a more thorough knowledge base. Many lab and field
experiments have shown that competition exists, but there is still considerable debate as to how
important it is in structuring communities (especially given latent effects such as indirect effects,
apparent competition, and ghosts of competition past). Once considered to be the
overwhelmingly key type of biotic interaction in structuring communities, competition is now
recognized as one of many types of interactions that structure communities (future lectures will
focus on predation, parasitism, and mutualism as examples of other such important interactions).
Competition may still play a vital role in structuring communities during times of resource stress.
Similarities between competition among plants in forest and beer companies:
http://www.youtube.com/watch?v=Atg-5Nqszxw
References:
Abramski, Z., M.L. Rosenzweig, and B. Pinshow. 1991. The shape of a gerbil isocline measured
using principles of optimal habitat selection. Ecology 72:329-340.
Bender, E.A., T.J. Case, and M.E. Gilpin. 1984. Perturbation experiments in community
ecology: theory and practice. Ecology 65:1-13.
Buchanan, G.A., R.H. Crowley, J.E. Street, and J.A. McGuire. 1980. Competition of sicklepod
(Cassia obtusifolia) and redroot pigweed (Amaranthus retroflexus) with cotton (Gossypium
hirsutum). Weed Science 28:258-262.
Connell, J.H. 1961. The influence of interspecific competition and other factors on the
distribution of the barnacle Chthamalus stellatus. Ecology 42:710-723.
Connell, J.H. 1983. On the prevalence and relative importance of interspecific competition:
evidence from field experiments. Am. Nat. 122:661-696.
Connolly, J. 1988. What is wrong with replacement series? Trends Ecol. Evol. 3:24-26.
Goldberg, D.E., and A.M. Barton. 1992. Patterns and consequences of interspecific competition
in natural communities: A review of field experiments with plants. Am. Nat. 139:771-801.
Gurevitch, J., L.L. Morrow, A. Wallace, and J.S. Walsh. 1992. A meta-analysis of competition in
field experiments. Am. Nat. 140:539-572.
Hairston, N.G. 1985. The interpretation of experiments on interspecific competition. Am. Nat.
125:321-325.
Marshall, D.R., and S.K. Jain. 1969. Interference in pure and mixed populations of Avena fatua
and A. barbata. J. Ecology 57:251-270.
Park, T. 1948. Experimental studies of interspecies competition. I. Competition between
populations of the flour beetles, Tribolium confusum Duvall and Tribolium castaneum Herbst.
Ecol. Monogr. 18:267-307.
Park, T. 1954. Experimental studies of interspecies competition. II. Temperature, humidity, and
competition in two species of Tribolium. Physiol. Zool. 27:177-238.
Park, T. 1962. Beetles, competition, and populations. Science 138:1369-1375.
Schoener, T.W. 1983. Field experiments on interspecific competition. Am. Nat. 122:240-284.
Tansley, A.G. 1917. On competition between Galium saxatile L. (G. hercynicum Weig.) and
Galium sylvestre Poll. (G. asperum Schreb.) on different types of soil. J. Ecol. 5:173-179.
Tilman D. 1989. Ecological experimentation: strengths and conceptual problems. Pp. 136-157 in:
Long-term Studies in Ecology: Approaches and Alternatives (G. E. Likens, ed.). SpringerVerlag, New York, NY.
Underwood, A.J. 1991. Experiments in ecology and management: their logics, functions and
interpretations. Austr. J. Ecol. 15:365-389.
Wiens, J.A. 1977. On competition and variable environments. Am. Sci. 65:590-597. [a citation
classic]