Overgrowth competition in encrusting bryozoan assemblages of the intertidal and infralittoral zones of Alaska
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Almost 2000 cheilostomatid–cheilostomatid (bryozoan) interactions were recorded from 110 rocks from intertidal and infralittoral zone locations at Kodiac Island in the Alaskan Boreal–Arctic. Intraspecific interactions were unusually rare; this may have resulted from inhibition of con-specific settlement by adult colonies. In one species, rank did vary as a function of depth. The proportion of determinate-species encounter-pairings (a pairing in which one competitor/species wins all encounters) and tied outcomes (whereby neither competitor/species wins or loses but are involved in a “standoff” or mutual overgrowth) increased from the upper midlittoral to the lower infralittoral. The assemblage of bryozoans formed a clear hierarchy, with a score of 0.83 on Tanaka and Nandakumar's transitivity index. Overgrowth dominants did not monopolise the assemblage. The most abundant species were mid- or lower-ranked competitors. The identity of the competitive species had a major influence on the outcome of encounters. Zooidal height and colony growth morphology were important factors determining overall overgrowth rank. The greatest number of interaction types was recorded on medium-sized (surface area >300 and <600 cm2) rocks, and the overall diversity of intertidal species was very high compared with studies conducted elsewhere. The high interaction and species diversity recorded may both have resulted from intermediate levels of disturbance.
KeywordsSpecies Diversity Abundant Species Intermediate Level Major Influence Interaction Type
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