Jochimsen, Marc C. (2007) Role of Community Structure for Invasion Dynamics. (Diploma thesis), Universität Osnabrück, Osnabrück, Germany, 85 pp.

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Abstract

A often discussed topic in community ecology is the hypothesis that communities with a higher diversity are more stable against environmental changes. The study at hand addressed the question whether fouling communities with two different successional stages differ in their persistence against changed environmental parameters. Fouling communities consist of sessile marine macrobenthic organisms that settle on all surfaces that are submerged in
seawater, including ship hulls. This is one reason why intercontinental ship traffic is regarded as the main vector for dispersal of non-indigenous species.
The present study examined this ecological question by transplanting 4 and 2 months old fouling communities on artificial settlement substrata from one study site to a second site in the same coastal ecosystem on the island of Madeira. Their stability was measured as change in species composition compared to local reference communities from the recipient site. The diversity and the amount of available settlement substratum in the communities were regarded as function of their age. The results of this study show that younger communities were less persistent against the change in environmental parameters induced by the transplantation and therefore converged more rapidly towards the species composition of the local reference communities. The speed of convergence was found to correlate significantly with the initial taxonomic and functional diversity of the communities, while the role of unoccupied settlement substratum in the transplanted communities remained less clear. The most important factor controlling the convergence process was the species identity and the ecological role of dominant species.
Older communities are more persistent against a change in environmental parameters. As a consequence, the longer fouling communities can establish on mobile substrata like ship hulls, the more likely they are to survive the transport and to reach new habitats where they have the
chance to persist. Single species from these communities can pose a threat of bioinvasion in the new habitat if they are able to reproduce and to disperse. Regular cleaning of ship hulls is one recommended action to avoid long-distance dispersal of non-native species

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