Article

We analyzed the spatial distribution of Marsilea strigosa, an aquatic fern, considering two life stages (vegetative and sexual) and interpreted results taking into account possible facilitation or competition effects among individuals as well as existing colonization strategies. Marsilea strigosa is distributed from Spain to the Black Sea. It is considered a rare species due its high habitat specificity and small fragmented populations. We surveyed 95% of the Balearic population of M. strigosa, covering a surface of approximately 1000 m2. Single life stage and bivariate distribution patterns were analyzed using second-order spatial analysis based on Ripley’s Kfunction. The relationship between vegetative and sexual node types is discussed. Aggregation of vegetative and sexual nodes was the only spatial point pattern found. The same results were obtained when both stages were analyzed together with bivariate function. We discuss the effect of life stage on the balance between competition and facilitation in dynamic environments. The importance of these two processes in colonization sites can best be understood by comparing them between different life stages.