Palaeoclimatic models help to understand current distribution of Caucasian forest species

Abstract

Spatial and temporal constraints on dispersal explain the absence of species from areas with potentially suitable conditions. Previous studies have shown that post-glacial recolonization has shaped the current ranges of many species, yet it is not completely clear to what extent interspecific differences in range size depend on different dispersal rates. The inferred boundaries of glacial refugia are difficult to validate, and may bias spatial distribution models (SDMs) that consider post-glacial dispersal constraints. We predicted the current distribution of 12 Caucasian forest plants and animals, factoring in the effective geographical distance from inferred glacial refugia as an additional predictor. To infer glacial refugia, we tested the transferability of the current SDMs based on the distribution of climatic variables, and projected the most transferable ones onto two climate scenarios simulated for the Last Glacial Maximum (LGM). We then calculated least-cost distances from the inferred refugia, using elevation as a friction surface, and recalculated the current SDMs incorporating the distances as an additional variable. We compared the predictive powers of the initial with the final SDMs. The palaeoclimatic simulation that best matched the distribution of species was assumed to represent the closest fit to the true palaeoclimate. SDMs incorporating refugial distance performed significantly better for all but one studied species, and the Model for Interdisciplinary Research on Climate (MIROC) climatic simulation provided a more convincing pattern of the LGM climate than the Community Climate System Model (CCSM) simulation. Our results suggest that the projection of suitable habitat models onto past climatic conditions may yield realistic boundaries of glacial refugia, and that the current distribution of forest species in the study region is strongly associated with locations of former refugia. We inferred six major forest refugia throughout western Asia: (1) Colchis; (2) western Anatolia; (3) western Taurus; (4) the upper reaches of the Tigris River; (5) the Levant; and (6) the southern Caspian basin. The boundaries of the modelled refugia were substantially broader than the refugia boundaries inferred solely from pollen records. Thus, our method could be used to: (1) improve models of current species distributions by considering the dispersal histories of the species; and (2) validate alternative reconstructions of palaeoclimate with current distribution data.

Phylogeography and morphological variation in a narrowly distributed Caucasian rock lizard, Darevskia mixta

“…The Greater Caucasus therefore, especially its central, the highest and the steepest part, has limited importance as a glacial refugium. Our study supports the existence of two distinct refugia in the Lesser Caucasus, based on the deep genetic differences between D. mixta lineages from the south-eastern Black Sea Coast, and central Georgia (Tarkhnishvili, Thorpe and Arntzen, 2000;Tarkhnishvili, Gavashelishvili and Mumladze, 2012). It suggests that the "Central Georgian" refugium was located in the eastern part of Meskheti Mountains (locations 1-2, fig.…”

“…Genetic studies of other small, less mobile animals, the Caucasian salamander (Mertensiella caucasica), for example, or the large endemic Caucasian snails (Helix buchi, H. goderdziana) (Tarkhnishvili et al, 2000;Mumladze et al, 2013), also suggest that humid forest refugia of the Western Caucasus (Zeist and Bottema, 1991;Tarkhnishvili et al, 2012;Tarkhnishvili, 2014) were historically fragmented, rather than continuous. According to these studies, the most prominent division was between current Central Georgia (where the entire range of D. mixta is located) and the southeastern Black Sea Coast (where the range of D. clarkorum, the sister species of D. mixta is located).…”

“…The current distribution range of D. mixta is fully associated with a Colchic humid forest refugium east of the Black Sea (Zeist and Bottema, 1991;Tarkhnishvili, Gavashelishvili and Mumladze, 2012), specifically with its easternmost part. Phylogeographic studies of smallbodied animals with limited dispersal ability (Tarkhnishvili et al, 2000;Mumladze et al, 2013) suggest that this refugium might be, in fact, subdivided into even smaller refugia and populations of salamanders, snails, and perhaps lizards of those refugia could be totally or partly isolated.…”

Phylogeography of the land snail genus Circassina (Gastropoda: Hygromiidae) implies multiple Pleistocene refugia in the western Caucasus region

“…The importance of the western Caucasus, especially the Colchis region, as a glacial refugium where, among others, Neogene relict species survived as well as a centre of ongoing radiation has increasingly been appreciated (Hewitt, 2000;Pokryszko et al, 2011;Tarkhnishvili et al, 2012;Nakhutsrishvili, 2013;Tarkhnishvili, 2014;Walther et al, 2014). There is dissent, however, on whether there existed a single continuous forest refugium at the eastern Black Sea coast as implied by some studies (van Andel and Tzedakis, 1996;Kikvidze and Ohsawa, 2001;Pokryszko et al, 2011;Tarkhnishvili et al, 2012;Volkova et al, 2013;Wielstra et al, 2013) or multiple forest refugia (Tarkhnishvili et al, 2000;Mumladze et al, 2013;Tarkhnishvili, 2014).…”

Gene introgression between Gazella subgutturosa and G. marica: limitations of maternal inheritance analysis for species identification with conservation purposes

“…The human activity caused substantial landscape changes in the region (Zazanashvili et al 2004;Abbo et al 2010;Tarkhnishvili et al 2012). Currently, the range of the gazelles is fragmented: the Caucasian geographic population is isolated (Mallon 2008) and, in addition, individual populations form smaller isolates in some parts within the "mainland" range (Durmuş 2010).…”