jabbrv-ltwa-all.ldf jabbrv-ltwa-en.ldf Adaptation to different environments in geographically separated populations is key for allopatric speciation. Most research has focused on the effects of geographical isolation and abiotic factors, but disjunct populations frequently co-occur with different pools species, favouring divergent adaptation and speciation. We show the importance of plant neighbourhood, compared to geographic and environmental factors, in the allopatric speciation across the Iberian Peninsula of two closely related plants, Carex elata and Carex reuteriana. Using regularized generalized linear models, we identified the key variables explaining distribution patterns. We also examined the relationships between inter-population genetic distances, using genomic data (genotyping-by-sequencing), and biotic, abiotic and geographic factors to understand the drivers of lineage splitting. Plant neighbourhood emerged as a stronger predictor of allopatric distributions than abiotic or geographic factors. Additionally, inter-population genetic distances were significantly associated with all the factors studied, albeit with varying degrees of influence. Notably, plant neighbourhood had the largest effect in C. elata, which showed the greatest population differentiation. These findings suggest that the biotic and microenvironmental factors influencing divergent plant neighbourhoods have significantly contributed to the differentiation of these taxa, providing new insights into the evolutionary processes shaping the origin and distribution of species.

Beta diversity patterns are essential for understanding how biological communities are structured. Geographical and environmental factors, as well as species dispersal ability, are important drivers of beta diversity, but their relative importance may vary across spatial scales. In this study, we evaluate whether beta diversity changes across geographical scales and analyse how different drivers affect turnover patterns of native seed plants in an oceanic archipelago, the Azores (Portugal). Using a 500 x 500 m resolution grid, we selected cells that are covered by one of the following habitats: native forest, naturalized vegetation and seminatural pastures. We calculated species turnover at three spatial scales: i) between islands, ii) between cells within each island, and finally iii) between cells of each of the habitats of interest in each island. We then calculated the contribution of dispersal syndromes (endozoochory, epizoochory, hydrochory and anemochory) to turnover at each of the scales. Lastly, we assessed the relationship between geographical and climatic distances and habitat composition with turnover. Turnover was higher at the smallest scale, particularly in seminatural pastures, and decreased with increasing spatial scales, a pattern potentially associated with the historical fragmentation and current patchy distribution of native forest and seminatural habitats in the Azores. Dispersal syndromes and habitat composition had a negligible effect on turnover at all scales. Geographical distance had a positive effect on turnover at all scales, increasing with scale. The relationship between turnover and climatic distance was only significant at the intermediate and small scales in specific islands and habitats. Scale plays an important role at determining the effect of the drivers of turnover, in particular geographical and climatic distance. These results highlight the need to carefully select the scale of analysis when studying turnover patterns, as well as identifying the potential drivers associated with each scale.