Factors that determine the occurrence of native and introduced Spergularia species in Mediterranean coastal ecosystems

ABSTRACT Background Studies have found a close correlation between the dispersal of alien species and anthropogenic disturbance. However, in coastal Mediterranean ecosystems, the importance of human induced vs. naturally occurring habitat heterogeneity in influencing the distribution of native vs. exotic species remains poorly understood. Aims Our aim was to identify plant communities where native and introduced Spergularia species occur, the associated soil conditions, the effect of anthropogenic activities, and how these factors determine their distribution in Odiel Marshes Natural Park. Methods The occurrence of seven Spergularia species was studied in 92 vegetation patches. These patches were analysed for plant species composition, edaphic variables (humidity, pH, salinity, organic matter content and particles >0.2 mm), degree of inundation, degree of alteration and level of protection. Results The distribution of 5 native species was related mainly to edaphic factors, while the distribution of 2 species was related to the degree of anthropic impact. Conclusions Spergularia species show three patterns of distribution: S. heldreichii, S. fimbriata and S. media do not occupy altered zones. S. salina and S. nicaeensis naturally inhabit undisturbed habitats, but human alterations have increased their distribution. The presence of S. bocconi and S. purpurea is due to human transformation of this area.