LANDSCAPE PATTERNS OF REEF CORAL DIVERSITY - A TEST OF THE INTERMEDIATE DISTURBANCE HYPOTHESIS

The intermediate disturbance hypothesis predicts that species diversity within habitats will be maximal at intermediate levels of disturbance, because competitive exclusion will be balanced by destruction of the competitive dominant(s). Previous tests of the hypothesis on coral reefs have produced variable results, in part because they were conducted at the small spatial scale of the quadrat. This study tested the intermediate disturbance hypothesis on a landscape scale, over an area >10(4) m(2) within a single reef habitat. Among replicate shallow reef spurs in Belize, coral species diversity was maximal at intermediate levels of disturbance, as measured by the topographic complexity of the substratum. Increased diversity at intermediate disturbance levels was due primarily to increased evenness rather than to increased species richness. The impacts of storm-generated debris appear to have reduced the cover of the competitively dominant coral, Agaricia tenuifolia Dana, allowing competitively subordinate coral species to increase on some spurs. This landscape-scale analysis provides the first rigorous, quantitative support for the hypothesis in a reef coral assemblage.