Dispersal and destruction in a multiple habitat system: An experimental approach using protist communities

Many habitats occur as discrete fragments, and the populations in such communities persist at a regional level, despite periodic local extinction. One component of local extinction is disturbance, or in the extreme case destruction, of individual patches. The impact of such disturbances on the ability of the entire system (the metacommunity) to retain species is clearly a significant question in many real systems. The problem has been the subject of a number of recent theoretical investigations, but this study addresses the question using an experimental 'model' system of protist communities, where patch destruction rates and between-patch dispersal rates can be manipulated. Replicate blocks of eight microcosms (patches) were inoculated with 13 species of protists and then subjected to 3 levels of destruction and 2 levels of between-patch dispersal in a factorial design. Communities were sampled after 6 and 16 weeks. The results support the simple prediction that metacommunities subject to higher rates of patch destruction suffer greater species losses, and that increasing dispersal rates between patches moderates, but does not entirely counteract, that effect. Differing dispersal rates alone had little effect on either community or metacommunity diversity. There was no evidence that disturbance enhanced diversity, either within or across patches, but there was some suggestion that there were consistent differences in community structure in response to combinations of destruction/dispersal treatments. The possible mechanisms underlying the results, including the effect of low local abundance on colonization rate, are discussed.