Competitive ranks of three Fucus spp. (Phaeophyta) in laboratory experiments?testing of Keddy's competitive hierarchy model

Abstract

Keddy's competitive hierarchy model describes species distribution patterns along gradients under equilibrium conditions and can potentially serve as an explanation for zonation patterns of intertidal seaweeds on rocky shores. One of the assumptions of the model is a competitive hierarchy with the top competitor occupying the benign end of the gradient. Another assumption is the consistency of competitive ranks of species in all environmental conditions included in the shared parts of species' fundamental niches. In laboratory replacement series experiments, the competitive ranks of pairs of Fucus species that occupy adjacent zones in the field were analysed and compared to ranks found in previous field experiments. Unattached thalli of Fucus serratus versus F. vesiculosus or F. vesiculosus versus F. spiralis, respectively, were held in aerated beakers to establish the competitive ranking of the three congeners. Each replacement series was conducted at three total densities. F. vesiculosus was clearly competitively dominant over F. serratus. In competition with F. spiralis, F. vesiculosus was only dominant at its lowest absolute input frequencies, but at higher frequencies dominance was reversed. At high densities, the total ranking was F. spiralis > F. vesiculosus > F. serratus, which is the opposite order to that which would be expected from Keddy's model. Although all three species thrived well under the laboratory conditions, the results did not reflect in situ competitive dominances, which may be an effect of nutrient competition in the laboratory. Keddy's assumption that competitive ranks are consistent over the whole range of fundamental niches cannot be supported for Fucus spp.

Can community composition be predicted from pairwise species interactions?

“…For example, many experiments are conducted in pots with artificial substrate, and are often conducted in glasshouses as opposed to field conditions. Hierarchies derived in artificial situations may less accurately predict field abundances than hierarchies constructed from conditions comparable to the field environment (Wilson and Keddy 1986;Karez 2003).…”

Differential nutrient uptake by two segregated red algae in an estuarine intertidal zone

“…As a general rule, physical factors control the upper zonation of intertidal habitats; whereas, biological interactions play a major role in the lower zones (Lewis 1964). Interspecific competence has been described for several marine benthic organisms (Connell 1972), including intertidal macroalgae (Chapman & Johnson 1990;Karez 2003). Species coexisting in a habitat compete for light, substrate, and nutrients (Lobban & Harrison 1994).…”

Competitive interactions in marine macroalgae: an analysis of the literature by boolean operators

“…In marine coastal systems, competition among macroalgae is considered one of the main processes structuring and determining patterns in the entire coastal environment (Paine 1990;Olson and Lubchenco 1990;Strong and Dring 2011). The most common limiting resources attributed to macroalgae growth are space, light and nutrients, which are highly connected (Schiel and Foster 1986;Karez 2003;Edwards and Connell 2012).…”