Niche breadth rather than reproductive traits explains the response of wetland monocotyledons to land-cover change

Question: We hypothesised that, even within the same plant functional group, there are specific distributions in land-cover classes and with land-cover change that are associated with niche breadth rather than reproductive strategy, and that the broader the niche of the species the better they cope with different land-cover classes and changes over time. Location: The Llobregat Delta (Barcelona, Spain). Methods: We analysed the distribution pattern of eight coexisting wetland perennial monocotyledons within human disturbance classes (obtained from the classification of land-cover categories in relation to their level of human disturbance) and changes in such classes from 1956 to 1999. We then compared species regional abundance and distribution patterns with seed dispersal type (wind dispersed versus non-wind dispersed species), vegetative spread (tussock versus caespitose-running species), and niche breadth (the number of phytosociological alliances in which each species is found). Results: Regional abundance of the species was positively related to niche breadth, but was independent of reproductive traits. Similarly, distribution in human disturbance classes and their changes were associated with niche breadth rather than reproductive traits. In general, the more specialist the species, (i) the more they are concentrated in natural habitats, (ii) the less land-cover changes they are able to cope with, and (iii) the more they are restricted to stable change types, particularly to longstanding natural areas. Conclusions: Ecological plasticity rather than dispersal capacity of dominant perennial monocotyledons determines their regional abundance and their ability to cope with recent and future land-cover changes in Mediterranean wetlands. As habitat specialists are less resistant to landscape change than generalists, floristic homogenisation may progress in these habitats with the likely scenario of increasing land-cover turnover. © 2009 International Association for Vegetation Science.