Species-area relations of communities on intertidal boulders: testing the null hypothesis

The major hypotheses advanced to account for the species-area relationship were reviewed. It was argued, in accordance with some earlier workers, that one of these - the Random Placement or Passive Sampling hypothesis - should be regarded as the null hypothesis, and be tested and rejected before other, more complex, hypotheses are proposed. This procedure was followed for the communities of sessile and mobile species on the tops and bottoms of boulders high and low on the shore on two rock platforms in New South Wales. In addition, the community on the rock platform near each boulder field was sampled but no consistent relationship between the diversity of these two types of community was found. 
Species-area curves were found in all the communities on boulders and some of these were significantly different from the curves expected under the Random Placement hypothesis. Results consistent with each of the hypotheses reviewed were found but no single hypothesis accounted for all the patterns in diversity observed. The Random Placement hypothesis was a good model for the species-area curves of more than half the communities sampled. The intermediate Disturbance hypothesis explained patterns in the diversity of communities low on the shore. The latter boulders were often disturbed by waves and buried by sand and these factors appeared to influence the diversity of the community. The patterns were, however, too complex to be interpreted only in terms of the effects of these factors.