Plant species segregation in dune ecosystems emphasises competition and species sorting over facilitation

Background: Coastal dunes are dynamic ecosystems, with vegetation seen as a key element in the response to a continuously changing environment. Aims: We explored co-occurrence patterns of plant species within dune ecosystems along a regional climatic and a local sea–inland gradient. Methods: Five habitat types were surveyed along a sea–inland transect at seven sites along a climatic gradient in Portugal. A multistep framework, considering the relevant scales and gradients, provided standardised scores of species co-occurrence (based on presence/absence and abundance data) for the whole study area and along the climatic and sea–inland gradients. Results: Species diversity was primarily related to the local sea–inland gradient. Co-occurrence analyses indicated the prevalence of species segregation, suggesting competition and species sorting across sites. Within each site, segregation prevailed, but tendencies for species aggregation were observed in some habitat types. Conclusions: To our knowledge, this is the first study evaluating species co-occurrences considering all habitat types within the whole dune ecosystem, analysing presence/absence and abundance data against regional and local gradients. Results converge with refined theories of community assembly, constituting added values for assessing multiscalar co-occurrence patterns of plant communities, and thus improving reporting of the condition of dune habitats and biodiversity.