Are bryophyte communities different from higher-plant communities? Abundance relations John B. Steel, J. Bastow Wilson, Barbara J. Anderson, Rachael H. E. Lodge and Raymond S. Tangney Steel, J. B., Wilson, J. B., Anderson, B. J., Lodge, R. H. E. and Tangney, R. S. 2004. Are bryophyte communities different from higher-plant communities? Abundance relations. / Oikos 104: 479  /486. The considerable differences in biology between bryophytes and higher plants have led to speculation that their community structure might be different. Ten bryophyte communities were sampled for species biomass composition, and for comparison ten higher-plant communities that were similar in physiognomy and in total community biomass. The rather insecure theory in the bryophyte literature was distilled into eight quantifiable predictions, which were tested. For seven, there was no sign of the predicted differences: i.e. no indication of the predicted low within-community heterogeneity, higher species richness, more variable species richness, lower rank consistency, a poor fit for the geometric model of RAD (relative abundance distribution), better fit for the broken-stick and general-lognormal RAD models with general-lognormal parameter g deviating further from 1.0, or of a good fit for the Zipf- Mandelbrot RAD model. However, evenness was, on average, significantly (p /0.005) less in the bryophyte communities, using any of four evenness indices. Two possible features of bryophytes are suggested that might cause this: (a) a smaller module (i.e. shoot, leaf) size, allowing species to be present with a lower threshold biomass, and (b) less efficient competitive exclusion among bryophytes because of weaker competition and apredominance of mutualism, as suggested in the literature. However, the striking conclusion from the results is that in spite of all the biological differences between the two groups of organisms, their community organisation is remarkably similar. J. B. Steel, J. B. Wilson, B. J. Anderson and R. H. E. Lodge, Botany Dept, Univ. of Otago, P.O. Box 56, Dunedin, New Zealand (bastow@otago.ac.nz).  / R. S. Tangney, Dept of Biodiversityand Systematic Biology, Natl Mus. and Gallery, Cardiff, UK, CF10 3NP. It has been suggested that the structure of bryophyte communities differs from that of higher (i.e. vascular) plant communities (Watson 1980, Slack 1990). Indeed, a difference could be expected from the biological differ- ences between the two groups of plants. Bryophytes receive little water from the soil and have poor water-loss control (Sveinbjornsson and Oechel 1992). They obtain nutrients from the soil only by splash (van Tooren et al. 1990). They have little support tissue, and often con- siderable shade tolerance (Bates 1998). These biological differences have implications for community structure, and it is our aim here to test these. For example, it has been suggested that lack of differentiation in water and light response may lead to a lack of partitioning in microhabitat (Frego and Carleton 1995). This can be tested by examining within- community heterogeneity, the prediction being that the patches within a superficially uniform bryophyte com- munity will show low dissimilarity in species composi- tion. Prediction 1: there will be low within-community heterogeneity in bryophyte communities. A key indicator of the many ecological, environmental and evolutionary forces acting on biological commu- nities is species richness. For example, the suggested Accepted 25 July 2003 Copyright # OIKOS 2004 ISSN 0030-1299 OIKOS 104: 479  /486, 2004 OIKOS 104:3 (2004) 479