Biology Reference
In-Depth Information
the other to local extinction if the strength of their competitive abilities is asym-
metrical, but they exhibit similar carrying capacities. Conversely, if the carrying
capacities of the two species are substantially different, the species with the larger
carrying capacity can drive the other species to local extinction even if their
competitive abilities are equal.
While numerous examples of competition among individuals and/or species
exist, debate over the general importance of competition as a structuring agent in
natural communities remains. On the one side, Weins (
1977
) argues that competition
among many species is actually rare in nature and that its importance as an agent of
natural selection is therefore minimal. On the other hand, Diamond (
1978
) supports
the view of Darwin (
1859
), who suggested that competition between closely related
species is a deterministic factor in natural selection. In fact, Darwin wrote “As the
species of the same genus usually have, though by no means invariably, much
similarity in habits and constitution, and always in structure, the struggle will
generally be more severe between them, if they come into competition with each
other, than between species of distant genera.” In discussing competition among
macroalgae specifically, Miller (
1967
) notes that competition can occur via direct
interactions in which one organism and/or species prevents the other from access to a
limited resource (interference competition) or via indirect interactions where the
species exploit a shared resource but do not directly interact with each other
(exploitative competition). However, given that different algal traits such as rapid
and/or indeterminate growth, large thallus size, and resistance to unfavorable envi-
ronmental conditions can be associated with different competitive interactions, it
may be difficult to identify if certain interactions are due to interference, exploita-
tion, or a combination of the two (Olson and Lubchenco
1990
). This problem can be
exacerbated considering that different ecologists will often use different
methodologies in their studies of competition and thus the results of their studies
may vary simply due to the experimental approached used (e.g., Underwood and
Fairweather
1986
), and that experiments aimed at identifying the responses to
competition may actually reflect only indirect evidence that it has actually occurred
(e.g., Connell
1980
). Consequently, demonstrating that competition is important to
structuring natural communities requires carefully planned combinations of field
observations to identify the patterns coupled with directed manipulative
experiments to determine the processes behind them. These methods often involve
removing one or more (e.g., the competitive dominant) species(s) and monitoring
responses in the other species under consideration. In fact, a large number of studies
have used these methods in studies of competition within macroalgal communities
and have largely demonstrated the importance of both interspecific and intraspecific
interactions as structuring agents. In this chapter, we review some of the main
developments associated with these concepts and provide examples from case
studies that demonstrate their importance. We focus our discussion on competition
among benthic macroalgae, although it should be noted that among bloom-forming
microalgae, both exploitative (i.e., for shared limited resources) and interference
(i.e., via allelopathy) competition can be important in structuring planktonic
communities, especially when the blooms are fully developed (e.g., Sol
´
et al.
2005
).
