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Date of Award

9-2002

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

Supervisor

Dr. Jurek Kolasa

Abstract

This dissertation examines the relationship between diversity and stability in aquatic rock pool invertebrate communities. Previous tests of the relationship between diversity and stability have suggested that diversity stabilizes communities properties but either destabilizes or is unrelated to population properties; however, a comprehensive test of the relationship between diversity and stability has not previously been conducted in aquatic ecosystems. I used two approaches to examine diversity-stability relationships in rock pools. First, I used time series data of population and community densities collected on 49 rock pool communities over 8 years, and second, I experimentally manipulated diversity and nutrient conditions in rock pool container habitats.

I found that diversity was negatively related to community variability in both natural unmanipulated rock pools and experimental rock pools consistent with the diversity-stability hypothesis. However, the stabilizing effect of diversity was modulated by environmental conditions. In natural unmanipulated rock pools strong correlations between diversity and community variability were identified in abiotically stable rock pools and temporary rock pools that were subject to frequent desiccation events. In contrast, there was no relationship between diversity and community stability in rock pools with variable abiotic conditions or permanent rock pools which were not subject to desiccation events.

That environmental conditions might modulate the relationship between diversity and stability was further confirmed experimentally. In experimental rock pools the responses of community and population stability to different diversities depended on nutrient conditions. Diversity stabilized both community and population densities in oligotrophic rock pools but not in mesotrophic or eutrophic rock pools. The stabilizing effect of diversity on community density supports previous studies in other ecosystems, however, this is the first study to show a stabilizing effect of diversity on population densities.

The results of this study suggest that under some conditions stability is dependent on diversity, however there is no necessary relationship between diversity and stability in rock pool communities. Furthermore, contrary to the general conclusions drawn from mathematical models and experimental studies in plant communities, populations may be stabilized rather than destabilized by diversity depending on the system under consideration.

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