Flora 215 (2015) 84-91 Contents lists available at ScienceDirect iFLORAl Flora ELSEVIER journal homepage: www.elsevier.com/locate/flora ,, l Effect of environment on distributions of rock ferns in the Mediterranean climate: The case of the genus Asplenium in Montenegro N. Bystriakova3*, M. Peregrymb, S. Dragicevicc 3 Department of Life Sciences, The Natural History Museum, Cromwell Road, SW5 7BD London, UK b O.V. Fomin Botanical Garden, Educational and Scientific Centre "Institute of Biology", National Taras Schevchenko University ofKyiv, 1 Symon Petlura Street, Kyiv 01032, Ukraine c Natural History Museum of Montenegro, TrgVojvode Becir Bega Osmanagica 16, Podgorica, Montenegro ^JJj^ CrossMark ARTICLE INFO ABSTRACT Article history: Received 28 April 2015 Received in revised form 10 July 2015 Accepted 15 July 2015 Edited by Karsten Wesche Available online 17 July 2015 Keywords: Multivariate analysis Generalised linear models Water deficit Indicator species Climate change The aim of this study was to explore the way in which environmental aspects influence distributions of rock flora of the Mediterranean basin, using the genus Asplenium as a study system. Using the most comprehensive dataset to date built with the data from museum collections and those obtained in the course of a field survey, we identified patterns of species richness, carried out multivariate analysis, and fitted generalised linear models to the presence/pseudo-absence and abundance data of the three wide-spread taxa. We complemented the information on climatic preferences of the Asplenium ferns by phytosociological data. Based on their distributions in the ecological space defined by temperature- and precipitation-related variables, the Asplenium ferns known for Montenegro were assigned to the three groups: coastal species, generalist, and highland species. Within these groups, no further niche differentiation could be detected given the available environmental factors. Phytosociological information from herbarium specimens was consistent with the results of the multivariate ecological analysis. Non-climatic environmental factors were limiting the distributions of the Asplenium ferns on the country-size scale, but were not statistically significant in separating niches among the species. Our results showed a significant impact of water deficit on the distributions of the two morphologically distinct and locally abundant species; these species can be recommended as potential indicators of the increasing water deficit stress in the European Mediterranean climate. Species richness patterns of the spleenworts of Montenegro suggested that the whole country was important for maintaining the diversity of this group of plants. This study demonstrates the value of natural history collections combined with field data to inform ecological research. For the first time, a numerical analysis of the data concerning distribution and abundance of the most common and wide-spread European ferns of the genus Asplenium in an area with the typical Mediterranean climate was carried out. © 2015 Elsevier GmbH. All rights reserved. 1. Introduction The pteridological flora of the Mediterranean basin consists of ca. 100 taxa (Pichi-Sermolli, 1979) and makes an important contribution in terms of species diversity to the vascular flora of this globally important hot-spot of biodiversity (Comes, 2004). Despite * Corresponding author. E-mail addresses: n.bystriakova@nhm.ac.uk (N. Bystriakova), peregrym@ua.fm, mykyta.peregrym@gmail.com (M. Peregrym), sneza.dragicevic@t-com.me (S. Dragicevic). http://dx.doi.Org/10.1016/j.flora.2015.07.003 0367-2530/© 2015 Elsevier GmbH. All rights reserved. that the Mediterranean Region has been recognised as a key area for the long-term survival of the species and genetic diversity of ferns (Vogel et al„ 1999), pteridophytes are currently underrepre-sented in ecological studies focused on the vegetation of Southern Europe. As a result, only a limited number of research reports on the subject has been published so far (e.g. Birks, 1976; Bona et al., 2007; Marquez et al., 1997; Prelli and Boudrie, 2002; Saiz and Lobo, 2008). The genus Asplenium L. represented in Europe by ca. 50 taxa (Tutin et al., 1993; Vogel et al., 1999) is an essential component of the Mediterranean fern flora. This is largely due to the preferences of the majority of the European Asplenium species for limestone N. Bystriakova et al. / Flora 215 (2015) 84-91 85 outcrops (Vogel et al., 1999) common in the region. Some aspects of ecology (life forms, associations with other species and plant communities) of the common species of Asplenium have been studied in detail (Database of Insects and their Food Plants, http://www. brc.ac.uk/dbif/hosts.aspx; Didukh, 2000, 2011; Prelli and Boudrie, 2002; Rašomaviéius,2007; Särbuetal., 2013; Soster,2001; Vasheka and Bezsmertna, 2012). However, the knowledge about spleen-worts' relationships with environmental factors remains limited (Troia et al., 2012). Anecdotal evidence suggests that species of Asplenium can have contrasting environmental preferences, despite their largely similar growth form and tendency to occupy similar substrates. For example, A. ceterach is known for its high drought tolerance (Zivkovic et al., 2010) which allows the species to grow in full sun, while A. scolopendrium prefers deeper, more protected crevices, and also occurs in forests (Reichstein, 1984). Whether the presumed differences in species' environmental niches can be adequately quantified given the available data on species distributions remains questionable (Bystriakova et al., 2012). The aim of this research was to identify the main environmental gradients separating species niches and limiting their distributions at the country-size geographic scale using the case of 10 species of the genus Asplenium distributed in Montenegro. Despite a relatively small area of just under 14,000 km2, the terrain of Montenegro ranges from sea level to 2500 m asi. (Bulié et al., 2011). Over two thirds of the terrain are dominated by karst formations (Radulovic and Radulovic, 1997). A combination of the distinct climatic gradients with calcium rich substrate found in abundance in a relatively small area makes Montenegro an ideal location for studying the ecology of spleenworts. Ecological descriptions of the Asplenium species of Montenegro - mostly in the form of brief characteristics of substrate preferences - are available from floristic literature (Bubanja, 2004; Bulié, 2008; Čurovié et al., 2011; Hadžiablahovic, 2010; Karaman, 1997; Menkovic et al., 2011; Mrdak et al., 2011; Pančié, 1875; Petrovié, 2004, 2005, 2011; Pulevié, 2005; Rohlena, 1942; Stečl 1 evié, 2001,2002; UNEP Vienna, 2010; Vladimírov et al., 2006 Čurovié et al., 2011; Hadžiablahovic, 2010; Karaman, 1997; Menkovic et al., 2011; Mrdak et al., 2011; Panéié, 1875; Petrovié, 2004,2005; Petrovié, 2011 Pulevié, 2005; Rohlena, 1942; Stečl evié, 2001Stečlevié, 2002 UNEP Vienna, 2010; Vladimírov et al., 2006). However, the wealth of information displayed on the labels of herbarium specimens appeared to be largely unreported. In the course of our project we captured not only collection localities available from herbarium specimens, but also phytosociological characteristics of habitats where species were collected. We complemented the data from herbarium collections and literature on species abundance data obtained in the course of a field survey covering the most fern species rich habitats of Montenegro. Specifically we were asking the following questions: (1) what are the environmental gradients separating niches among Asplenium species in Montenegro? (2) Do phytosociological characteristics of species obtained from literature, herbarium specimens and field records support the results of the niche analysis? (3) What environmental factors control distributions of Asplenium species on the country-size geographic scale? 2. Material and methods 2.1. Distribution data According to the available literature, the ferns of Montenegro comprise 40 species from 16 genera, of which 12 belong to the genus Asplenium (Rohlena, 1942; Pulevic, 2005; Stesevic and Berg, 2015). We used two distinct datasets to conduct our study: Dataset 1 consisted of presence-only distribution records (483 unique localities in total) of 10 species of Asplenium (Table 1 and Table 1 Species of the genus Asplenium in Montenegro selected for the study. Species and authorities Acronym Number of records (Dataset 1+Dataset 2) A adiantum-nigrum L. complex aspadi 85(78 + 7) A ceterach L. complex aspcet 187(118 + 69) A fissum Kit ex Willd. aspfis 56(50 + 6) A lepidum C. Presl asplep 6(6+0) A petrarchae DC. asppet 1(1+0) A ruta-muraria L. asp rut 87(55 + 32) A scolopendrium L. asp sco 17(17 + 0) A septentrionale (L.) Hoffm. aspsep 7(6+2) A trichomanes L. complex asptri 181 (125 + 56) A viride Huds. aspvir 33(27 + 6) Table SI) obtained by georeferencing specimen information held by seven herbaria (Table S2); Dataset 2 consisted of 131 presence/true absence records of seven species (Fig. SI) and was assembled in the course of fieldwork carried out in 2013. As part of Dataset 2, 30 plots were selected so that they were at least 1 km apart from each other and from the georeferenced locations of Dataset 1. In each plot with the size of 5 m x 5 m, the numbers of viable individuals of all identified species of Asplenium were recorded. Here we treat A. adiantum-nigrum in its wider taxonomic sense by including A cuneifolium and A onopteris (Tutin et al., 1993). The collected specimens were deposited in the Herbarium of the Natural History Museum, London, UK (BM); Herbarium of the Natural History Museum of Montenegro, Podgorica, Montenegro; and Herbarium O.V. Fomin Botanical Garden of the National Taras Schevchenko University of Kyiv {I|z|) error A. ceterac/i/intercept -0.617 0.120 -5.129 <0.0001 Temperature seasonality (BI04) 0.230 0.131 1.753 0.0796 Water deficit 0.505 0.137 3.703 0.0002 Slope -0.397 0.134 -2.955 0.0031 A. ruta-muraria /intercept -2.930 0.459 -6.384 <0.0001 Limestone 1.950 0.484 4.028 <0.0001 Open spaces -1.597 0.618 -2.583 0.0098 A. trichomanes /intercept 0.163 0.330 0.493 0.6223 Limestone -0.722 0.355 -2.035 0.0418 Sandstone -0.673 0.419 -1.607 0.1080 3.3. Correlations of species distributions with environmental variables The amount of variation explained by the regression models was low for all species when presence/pseudo-absence data from the Dataset 1 were analysed using a generalised linear model; less than 10% for A ceterach complex and A ruta-muraria, and less than 1% in the case of A trichomanes complex. In the case of A ceterach complex, temperature seasonality and water deficit were positively correlated with species' presence, while the effect of slope was negative. The distributions of A ruta-muraria and A trichomanes complex were not significantly related to any of the climatic variables; however, the dominant parental material and type of land cover (in the case of A ruta-muraria) made significant contribution to the models (Table 4). Table 5 Coefficients and significance values of generalised linear models (family "poisson") fitted to Dataset 2 (abundance records). Parameter Estimate Standard z value Pr(>|z|) error A. cererac/i/intercept 1.942 0.090 21.560 <0.0001 Temperature seasonality (BI04) -0.273 0.054 -5.079 <0.0001 Water deficit 1.003 0.092 10.891 <0.0001 A. rura-muraria/intercept 0.923 0.182 5.073 <0.0001 Water deficit -1.057 0.155 -6.804 <0.0001 Forest -0.665 0.247 -2.690 0.0071 A. trichomanesjintercept 1.765 0.147 12.003 <0.0001 Temperature seasonality (BI04) -0.473 0.133 -3.554 0.0004 Water deficit 0.230 0.135 1.697 0.0896 Sandstone -0.829 0.356 -2.330 0.0198 Slope 1.024 0.078 13.058 <0.0001 When Dataset 2 was considered, the amount of variation explained by regression models fitted to the abundance records was higher for all species: 49.3% in the case of A ceterach complex; 46.2% in the case of A ruta-muraria, and 61.1% in the case of A trichomanes complex. The relationship between water deficit and species abundance was positive in the case of A ceterach complex, and negative in the case of A ruta-muraria complex (Table 5). The model for A trichomanes complex had the largest number of variables, including slope and type of dominant parental material. 4. Discussion 4.1. Ecological niche differentiation among Asplenium species Vegetation type, substrate and terrain did not play a role in separating species' niches in environmental space. However, the combined effect of climatic variables successfully identified three broad ecological groups. The four species (A scolopendrium, A ruta-muraria, A trichomanes and A ceterach) with largely overlapping and relatively wide climatic niches positioned close to the overall mean habitat were identified as generalists. The group consisting of A adiantum-nigrum and A petrarchae was associated with the coastal areas characterised by the typical Mediterranean climate, with low temperature fluctuations around the year, but uneven distribution of precipitation. Although A petrarchae was represented in the study by a single collection locality, its preference for stable temperature and ability to tolerate periods of drought revealed by the ecological niche analysis was consistent with previous reports (Marquez et al., 1997). The climatic niche of A adiantum-nigrum had its centre in the area of Mediterranean climate with the highest temperatures and seasonal precipitation; however, several collection localities were found well outside the core distribution. Such heterogeneity of the niche poses questions about either the taxonomy of this species, which in the present study was treated in its broad sense, or the impact of allopolyploidy on niche limits (see Vogel et al., 1996). The role of polyploidy in the definition of niche limits may also be important for understanding the wide environmental ranges of the "generalists", of which three out of four are actually species complexes including diploids and polyploids (Vogel et al., 1996, 1999; Pinter et al., 2002; Trewick et al., 2002). The group consisting of the remaining four species (A lepidum, A flssum, A septentrionale and A viride) was associated with the highlands of the central and northern part of the country; this group was characterised by relatively narrow climatic niches. According to our results, the two utilized approaches (environmental niche modelling and phytosociological approach) were largely complementary. All studied species were recorded in Asple-nietea trichomanis vegetation class, which is typical of rocky cliff N. Bystriakova etal./Flora 215 (2015) 84-91 89 crevices and stone walls in Europe, North Africa, Middle East, Arctic islands and Greenland. In these habitats plants experience various forms of stress (nutrient limitation, water shortage, temperature fluctuations), and as a result of reduced competition weak colonizers such as Asplenium species have a better chance to establish and proliferate. The species identified by ecological niche modelling as generalists were found in the largest number of vegetation classes (maximum of six in the case of A trichomanes) ranging from rocky habitats and alpine grasslands to temperate grasslands, steppe, woodlands and shrublands. The group of ferns associated with coastal habitats, in addition to Asplenietea trichomanis vegetation class, was recorded in temperate woodlands only. The group of highland species was confined to montane habitats, with a single species (A.flssum) also recorded in temperate woodlands. Presence of A ceterach and A trichomanes in grassland and forest should be regarded as an exception, because these vegetation types do not provide the optimum ecological conditions for the species, the survival of which depends on the existence of microhabitats characterized by specific substrates and water availability. The fact that our two rather different approaches, environmental niche modelling and phytosociological approach, yielded essentially similar results gives credibility to our inferences. 4.2. Environmental constraints on distribution ofgeneralist species The species identified by multivariate analysis as generalists (A scolopendrium, A ruta-muraria, A trichomanes and A ceterach) appeared to be less dependent on climate compared with coastal and highland species as shown by their relatively wide climatic tolerance and their close position to the overall mean of the habitat (cross point of the horizontal and vertical axes in Fig. 3). To test the relationships between all available environmental variables and presence/pseudo-absence data for the three species identified as generalists (A ruta-muraria, A trichomanes and A ceterach) we used generalised linear models. The low amount of explained variation (typically less than 10%) confirmed that the distribution of the selected species was poorly explained by the environmental parameters given the available data. When abundance data (Dataset 2) were used, the amount of explained variation increased substantially (up to 46-61%). Thus the seemingly low dependence on climate appeared to be an artefact of incomplete sampling and/or inability to obtain true absence (as opposed to pseudo-absence) data. In addition to the climatic variables, characteristics of substrate, topography and land use type were making significant contribution to all models. Although the contribution of these variables was not consistent across the models (i.e. different variables were significant depending on the type of the data used), in most cases the relationships of these variables with species' distribution data appeared to be ecologically meaningful. For instance, the negative relationship with slope in the case of A ceterach (presence/pseudo-absence dataset only) can be attributed to the high drought tolerance of the species which enables colonisation of hotter and drier habitats at lower elevations. Due to the lack of the true presence/absence data, the relationships between environmental variables and species distributions recovered by our study are likely to reflect differences between the species' habitats rather than between those species and the general environment of the study area. In the abundance models, the effect of water deficit on species' distributions was significant and positive (i.e. species' abundance increased with the increased water deficit stress) in the case of A ceterach and negative (i.e. species' abundance decreased with the increased water deficit stress) in the case of A ruta-muraria. Water deficit effectively integrates the combined effects of solar radiation, evapotranspiration, and air temperature on watershed conditions given available soil moisture derived from precipitation. In a Mediterranean climate, climatic water deficit can also be thought of as a surrogate for water demand based on irrigation needs, and changes in climatic water deficit effectively quantify the supplemental amount of water needed to maintain current vegetation cover, whether natural vegetation or agricultural crops (Stephenson, 1998). The Mediterranean basin has been identified as one of the world's regions most vulnerable to climatic and anthropogenic changes (Doblas-Miranda et al., 2014), with one of the major threats to the current vegetation in the region being increasing drought stress (Milano et al., 2013). Because the abundance of the two species, A ceterach and A ruta-muraria, included in the present study was shown to be closely related to water deficit, these species can be considered as potential indicators of climate change. Moreover, they are locally plentiful and easily recognised due to their distinct morphology; counts of their abundance can be easily obtained by anyone with basic training in taxonomy. We therefore argue that it is worthwhile to consider plot counts of A ceterach and A ruta-muraria as an alternative way of monitoring changes in water availability. It is worth mentioning that the abundance data were collected in a small part of the species' distribution range in only 30 plots; yet the explanatory power of the regression models fitted with the abundance data increased substantially compared with those fitted with the presence/pseudo-absence data collected over a wider geographic extent. Our results corroborate the findings of Howard et al. (2014), who achieved large improvements in the ability to predict species distributions when abundance data were used. 5. Conclusions Intrinsic limitations of datasets sourced from biological collections, including difficulty to assemble, inaccurate, incomplete, and difficult to interpret or absent information about collection localities, taxonomic errors, and incomplete and selective sampling have been discussed in detail elsewhere (Boakes et al., 2010; Graham et al., 2004; Ponder et al., 2001; Pyke and Ehrlich, 2010). When small rock ferns are used in ecological research as a study system, additional difficulties arise from potential failure to capture environmental preferences of the species, due to low resolution of predictors or their inability to describe important environmental properties of micro-niches, as well as from inability to account for potential effects of breeding system on the properties of the environmental niche (Bystriakova et al., 2012; De Groot et al., 2012; Wubs et al., 2010) and the requirements of gametophyte (Testo and Watkins, 2013). Although the basis of the present study is formed by herbarium collections prone to the limitations described above, we show that the ecological relationships resulting from the analysis of the available distribution data were largely consistent with anecdotal evidence from literature and phytosociological information; these relationships were also supported by the results of the analysis of detailed species abundance data obtained from field-work. Acknowledgements We wish to thank the following individuals: Dr Olja Vasic (The Natural History Museum of Belgrade, Serbia), Dr. Goran Anackov (University of Novi Sad, Serbia), Dr. Snezana Vukojicic (University of Belgrade, Serbia) for their assistance with data assembling and for enabling access to herbarium collections; Dr. Olesya Bezsmertna (National Taras Schevchenko University of Kyiv, Ukraine), for her assistance with databasing and georeferencing of herbarium specimens and data from literature; Dr. Sci. Anna Kuzemko (National Dendrological Park "Sofievka" for the National Academy of Sciences 90 N. Bystriakova et al./Flora 215 (2015) 84-91 of Ukraine, Uman'), for her expert advice on vegetation classification. We thank Dr. Harald Schneider (The Natural History Museum, London) for his comments on the draft of the manuscript. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.Org/10.1016/j.flora.2015.07.003 References Aleksandrova, V.D., 1969. Klassifikatsia Rastitelnosti [Classification of Vegetation. A Review of Principles of Classification and Classification Systems in Different Geobotanical Schools]. Nauka, Leningrad. Birks, H.J.B., 1976. The distribution of European pteridophytes: a numerical analysis. New Phytol. 77, 257-287. Boakes, E.H., McGowan, P.J.K., Fuller, R.A., Chang-qing, D., Clark, N.E., O'Connor, K., Mace, G., 2010. 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