A New Method for Characterizing Surface Roughness and Available Space in Biological Systems

Surface roughness and available space for organisms inhabiting heterogeneous habitats have important effects on measurements of species diversity, population abundance and dispersal. Quantifying habitat complexity is important but very difficult to achieve, especially at small scales. 2. A method of quantifying topographic roughness is described, which produces estimates of space potentially available to organisms in different size classes rather than giving general descriptors. The method uses samples of profiles across the surface of interest that are taken over any spatial scale and that are then analysed by a low-cost, image-processing technique. 3. A case study shows that the method allows quantification of the effects of surface texture on abundance of stream algae. Stream stones differing in geological rock type differed in roughness at very small spatial scales (crevices < 0.4 mm in size). Chlorophyll a concentrations were correlated positively with roughness measured at the smallest spatial scale (0.2 mm). A colonization experiment, in which bricks were sandblasted to produce rough surfaces, showed that rough substrata attain higher abundances of stream algae than smooth. The imaging technique permitted the quantification of the exact differences in texture between smooth and rough surfaces while demonstrating that both rough and smooth bricks still fell within the natural range of texture shown by stream stones