Competition, a Major Factor Structuring Seaweed Communities

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 processes 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 interand intraspecific interactions (Creese and Underwood 1982), especially as they relate to each species’ own carrying capacity. Here, one species may drive