Biology Reference
In-Depth Information
Chapter 7
Competition, a Major Factor Structuring
Seaweed Communities
Matthew S. Edwards and Sean D. Connell
7.1 Competition Theory
Competition for shared resources has long been viewed as an important structuring
agent in natural communities (Gause
1934
; Strong
1980
). Generally defined as the
simultaneous use of limited resources by two or more organisms, competition can
negatively impact population growth rates and influence community-level pro-
cesses such as predation and/or how species respond to disturbances (Roughgarden
1979
). This can occur between individuals of the same species or among
individuals of different species. Early mathematical models such as those posed
by Lotka (
1925
) and Volterra (
1926
) and later demonstrated by Gause (
1934
)
suggest that when competition between two species is asymmetrical, one species
will eventually drive the other to local extinction in their “struggle for existence.”
However, these models do not include the effects of other factors (e.g., predation,
herbivory, environmental heterogeneity, or extreme environmental conditions)
which often mediate the strength and outcome of competitive interactions
(reviewed in Olson and Lubchenco
1990
). In fact, even though two species rely
on a shared resource, they may not compete if that resource is not limited or if the
effects of other factors such as grazing or disturbances are substantially greater.
However, when the shared resource is limited and competition for it is strong
relative to other factors, the outcome of competition may vary as a function of
both inter- and intraspecific interactions (Creese and Underwood
1982
), especially
as they relate to each species' own carrying capacity. Here, one species may drive
M.S. Edwards (
*
)
Department of Biology, San Diego State University, 5500 Campanile Dr., San Diego,
CA 92182, USA
e-mail:
edwards@sciences.sdsu.edu
S.D. Connell
Southern Seas Ecology Laboratories, School of Earth and Environmental Sciences,
University of Adelaide, DP 418, Adelaide 5005, Australia
