Species Richness of Stream Stones: An Investigation of the Mechanisms Generating the Species-Area Relationship

In an upland fourth-order stream, the fauna dwelling on both natural and artificial stones was found to be highly correlated with stone surface area. The power function model provided a good description of the species-area relationship of the stones. For both types of stones, passive sampling was rejected as an explanation for the species-area relationship. The compilation of cumulative species richness, proceeding in order from the smallest area to the largest area and vice versa revealed a negative fragmentation effect. Groups of small stones harboured an impoverished fauna compared with large stones of the same surface area. Small stones did not harbour a distinctive fauna, but simply a sub-set of the species found on larger stones