Indirect effects occur when the interaction between two species is influenced by a third species. Recent empirical and theoretical evidence suggests that indirect effects have important influences on population regulation and community structure. Most studies of indirect effects have examined chains or networks of predation or competition. Indirect effects can also involve other types of interactions, yet their role in structuring communities is rarely considered. One such interaction, biological habitat modification, is ubiquitous in marine habitats, especially through the alteration of sediments or the creation of hard substrates. In soft-bottom habitats, the shells of dead molluscs are important for shelter or attachment of many organisms, and mollusc predators should have strong indirect effects on the community by regulating the availability of these substrates. Because shells are produced by living organisms, their abundance and quality will also be influenced by the dynamics of the mollusc population and by processes that destroy or alter the shells. / I examined the indirect effects of the horse conch (Pleuroploca gigantea), a predatory gastropod, on a suite of fish and invertebrates that use bivalve shells (the pen shell Atrina rigida) as shelters and/or nest sites in St. Joseph Bay, Florida. Exclusion experiments indicated that horse conchs are a major source of Atrina mortality. Experimental additions of new shelters caused an increase in abundance and reproductive activity in three species of fish (two blennies and a clingfish). Increased rates of shell availability caused an increase in reproductive output for both individuals and the local population of Chasmodes saburrae, the Florida blenny, probably because new shells provide a greater surface area for eggs compared to older shells. I used a simulation model, based on measurements of natural variation in Atrina population and shell resource dynamics, to compare the relative effects of horse conch predation and other factors on Chasmodes. Although pen shell density had the strongest effect, horse conch abundance also strongly influenced blenny reproduction. Thus, both the field experiments and the model predict that, by regulating the availability of new shells, the horse conch has a positive indirect effect on reproduction in Chasmodes. / Source: Dissertation Abstracts International, Volume: 57-04, Section: B, page: 2296. / Major Professor: William Herrnkind. / Thesis (Ph.D.)--The Florida State University, 1996.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_77717 |
| Contributors | Kuhlmann, Mark Louis., Florida State University |
| Source Sets | Florida State University |
| Language | English |
| Detected Language | English |
| Type | Text |
| Format | 164 p. |
| Rights | On campus use only. |
| Relation | Dissertation Abstracts International |
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