Distributional ecology of Noccaea vesicaria in relation to the Anatolian Diagonal

: Anatolia is located at the intersection of three of the world’s 36 biodiversity hotspots (the Caucasus, Irano-Anatolian, and Mediterranean Basin biodiversity hotspots) and has about 10,000 plant species, over 3000 of which are endemic. Among the many reasons for the astonishing biodiversity of Anatolia, one that stands out is the Anatolian Diagonal. Although the Anatolian Diagonal has long been recognized as a biogeographical boundary between Central and Eastern Anatolia, its exact functioning is still not well understood. Thus, in this study, our aims were 1) to assess the environmental barrier function of the Anatolian Diagonal for a plant species, Noccaea vesicaria , living on and to the east of it; 2) to evaluate climate-driven range shifts (contractions or expansions), especially through the Quaternary glacial–interglacial cycles; and 3) to contribute to the long-standing debate on the causes of the floral break between the west and east of the Anatolian Diagonal. Accordingly, we used an ecological niche modeling approach with presence records and bioclimatic data. Under the present bioclimatic conditions, areas of more suitable bioclimatic conditions were observed, especially throughout and to the east of the Anatolian Diagonal, therefore largely matching the geographical distribution of N. vesicaria . However, areas of high bioclimatic suitability were also observed to the west of the Anatolian Diagonal, especially throughout the Taurus Mountains and Pontic Mountains. Thus, bioclimatic suitability by itself cannot explain the geographical distribution of N. vesicaria or the absence of it, especially to the west of the Anatolian Diagonal. Under the past bioclimatic conditions, areas of high bioclimatic suitability contracted during warmer time periods and expanded during colder time periods, suggesting that the geographical distribution of N. vesicaria contracted and expanded during warmer and colder time periods, respectively, at least around and in the Anatolian Highlands. There may be two reasons why N. vesicaria does not occur to the west of the Anatolian Diagonal: dispersal and/or biotic interactions (e.g., competition and facilitation). Biotic interactions (likely positive plant interaction or facilitation) may have played a significant role in shaping the geographical distribution of N. vesicaria , because it seems to be highly associated with the Anatolian Highlands steppe order Festuco oreophilae-Veronicetalia orientalis Hamzaoğlu whose range does not extend to Central Anatolia.