A simple mathematical model of competition is developed that includes two alternative mechanisms promoting successional diversity. The first underpins the competition-colonization hypothesis in which early successional species are able to persist because they colonize disturbed habitats before the arrival of late successional dominant competitors. The second underpins the niche hypothesis, in which early successional species are able to persist, even with unlimited colonization by late successional dominants, because they specialize on the resource-rich conditions typical of recently disturbed sites. We modify the widely studied competition-colonization model so that it also includes the mechanism behind the niche hypothesis. Analysis of this model suggests simple experiments that determine whether the successional diversity of a field system is maintained primarily by the competition-colonization mechanism, primarily by the niche mechanism, by neither, or by both. We develop quantitative metrics of the relative importance of the two mechanisms. We also discuss the implications for the management of biodiversity in communities structured by the two mechanisms. \u
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