Acta Herpetologica 13(2): 155-163, 2018 ISSN 1827-9635 (print) © Firenze University Press ISSN 1827-9643 (online) www.fupress.com/ah DOI: 10.13128/Acta_Herpetol-22830 Short term spatial structure of a lizard (Darevskia sp.) community in Armenia Neftalí Sillero1,*, Elena Argaña1, Susana Freitas2,3, Enrique García-Muñoz2, Marine Arakelyan4, Claudia Corti5, Miguel A. Carretero2 1 CICGE Centro de Investigação em Ciências Geo-Espaciais, Faculdade de Ciências da Universidade do Porto (FCUP), Observatório Astronómico Prof. Manuel de Barros, Alameda do Monte da Virgem, 4430-146, Vila Nova de Gaia, Portugal. *Corresponding author. E-mail: neftali.sillero@gmail.com 2 CIBIO Research Centre in Biodiversity and Genetic Resources, InBIO, Universidade do Porto, Campus de Vairão, Rua Padre Armando Quintas, Nº 7. 4485-661 Vairão, Vila do Conde, Portugal 3 Department of Animal and Plant Sciences, The University of Sheffield, Sheffield S10 2TN, UK 4 Faculty of Biology, Yerevan State University, Alek Manoogian 1, 0025, Yerevan, Armenia 5 Museo di Storia Naturale dell’Università di Firenze, Sezione di Zoologia “La Specola”, Via Romana 17, 50125 Firenze, Italia Submitted on: 2018, 6th March; revised on: 2018, 18th September; accepted on: 2018, 30th September Editor: Simon Baeckens Abstract. Factors driving the spatial patterns of communities of sedentary organisms are still poorly understood. In this context parthenogenetic animals are useful to test the contribution of sexual and interspecific interactions on spa- tial patterns. As such, mixed communities of asexual and sexual species are expected to be spatially organized as a single sexual species, with sexes randomly distributed and mutually independent. During the reproductive period, we determined the instantaneous spatial structure in a community of Darevskia rock lizards from Armenia composed of one sexual species (D. valentini), two asexual species (D. armeniaca, D. unisexualis), and their hybrids. We also ana- lysed the specific composition of clusters and the species segregation by habitat. We used the Ripley’s K distance func- tion to measure clustering spatial patterns, and the Delaunay’s triangulation to identify the clusters and their specific composition. We estimated the spatial segregation among species by calculating the overlap between species pairs, by comparing pairwise distances from males to other males and from males to females, and by comparing the frequen- cies of both sexes and reproduction modes (asexual and sexual) in plant cover and height using log-linear models. Species displayed a clustered spatial structure, with parthenogens (mainly D. armeniaca) or their hybrids in all clus- ters. Females and males were concentrated in areas with medium plant cover. D. armeniaca and D. valentini were the species with the highest overlap. Males were closer to males than to females. This community displays an instantane- ous spatial pattern resembling a population of a single sexual species. Spatial statistics offer new insights to analyse the spatial structure of species communities. Keywords. Armenia, Darevskia, GIS, local distribution patterns, spatial statistics. INTRODUCTION The analysis of the short-term spatial structure within a community of species with low dispersal allows understanding how individuals share the space and mod- ify their home ranges depending on the presence of oth- er species (competitors, predators, prey items) or other environmental factors (temperature, shelters) (Sillero and Goncalves-Seco, 2014; Sillero and Gomes, 2016). Contra- ry to home range analyses on the spatial needs of single individuals, species distribution analysis focuses on the presence of one or more species in a particular geograph- 156 Neftalí Sillero et alii ical area characterized by certain environmental variables (mainly climate) at coarse scales (regional or continen- tal) (Sillero et al., 2014; Sillero and Gomes, 2016). Link- ing both analytical levels, community spatial distributions can identify the main environmental factors with a high spatial resolution, applying techniques of species distribu- tion studies to the same scale of home ranges but during short time periods and with a different purpose. Namely, the community spatial distribution approach aims at pro- viding a snapshot of the multispecies spatial patterns at a local scale. As such, species’ interactions can be revealed without collecting repeatedly individual data (as required for home range studies). Species within a community can be distributed ran- domly, regularly, or in clusters (Gorton et al., 1979; Frost and Bergmann, 2012). Random distributions are typical of non-territorial or non-competing species living in hab- itats with abundant and widespread resources. The proba- bility of finding an individual is the same across the study area and independent from the presence of other indi- viduals. Species can be regularly distributed when indi- viduals avoid being mutually close (due competition or territoriality) and resources are evenly distributed. Spe- cies appear clustered when the resources are irregularly distributed, hence, the probability to find either a second individual near the first or areas without individuals is higher than expected by random. Clustering is the most frequent pattern observed in communities (Underwood and Chapman, 1996) with variable intensity (Moody et al., 1997). However, distribution patterns may also shift in time. For instance, some species shift from regular to clustered distribution as population density increases (Gorton et al., 1979). Many potential factors may drive the spatial structure of a multispecies community, including the distribution of energy or matter sources (light, water, soil nutrients, food), availability of shelters and resting places, presence of other species (predators, competitors, parasites), mates and other conspecifics. In animals, few studies describe how populations are locally distributed (Frost and Berg- mann, 2012; Sillero and Gonçalves-Seco, 2014) and even less considered as well species interactions (Underwood and Chapman, 1996). Therefore, the factors driving the distribution pattern of a community are still poorly understood. In this context, the spatial ecology of parthe- nogenetic (all-female) species can be particularly elucida- tive as it may provide insights on the contribution of sex- ual reproduction to species’ spatial patterns. Are parthe- nogenetic species using the space in a similar way as their sexual relatives? How are both types of species spatially organized when they coincide? In particular, partheno- genetic lizards can provide an excellent model system for testing the effects of sexual and interspecific interactions on spatial patterns. Some studies analysed the home ranges of single parthenogenetic lizards (Eifler and Eifler, 1998; Galoyan, 2013), but only Sillero et al. (2016) considered several species in sympatry and none analysed the community spatial distributions. According to the lizard literature, adult males and females often are randomly distributed, while juveniles have a regular distribution, as they are excluded to less suitable habitats (Frost and Bergmann, 2012; Sillero and Gonçalves-Seco, 2014). In principle, a population of a parthenogenetic species may have a more clustered distribution. In fact, our non-systematic observations reported groups of many females basking together in the same spot, as expected from the lack of mate competition and aggregation for resources. How- ever, following Sillero et al., (2016), if a mixed commu- nity composed of asexual and sexual species behaves like a population composed by a single sexual species, we should expect a similar spatial pattern: both sex- es distributed randomly (Frost and Bergmann, 2012). Therefore, if there is no competition for limited resourc- es but only interferences among individuals (Žagar et al., 2015) of asexual and sexual species, we should expect their distributions to be mutually independent (depending only on conspecifics and resources). On the contrary, if they compete for space we should expect larger distance between heterospecifics than between conspecifics. The main aim of this work is, hence, to analyse the instantaneous spatial structure of a lizard mixed commu- nity in order to determine whether different species seg- regate spatially or not. Here, we studied a community of lizards in true sympatry composed of several Darevskia species (Darevskia armeniaca, D. valentini, D. unisexu- alis) and their hybrids at Kuchak, Armenia (Danielyan et al., 2008). The genus Darevskia (Arribas, 1999), the first vertebrate group where parthenogenesis was described (Darevsky, 1967), occurs across all Caucasus, adjacent regions of Asia Minor, northern Iran and Balkans. A total of 25 sexual species and seven parthenogenetic forms have been described (Darevsky, 1967; Fu et al., 1995; Murphy et al., 1996; Arnold et al., 2007; Freitas et al., 2016b) although their phylogenetic relationships and tax- onomy are still under discussion. In Armenia, up to nine Darevskia species occur along a relatively small area and frequently overlap locally (Arakelyan et al., 2011). Specifi- cally, the aims of this study are: (1) To determine whether the short-term spatial structure of a community of lizards displays a clustered, random, or regular distribution. We predict that the spe- cies will not be distributed randomly or regularly along 157Spatial structure of a lizard community the study area, but in clusters, largely determined by the spatial structure of the area. (2) To identify the community clusters and their spe- cific composition. We hypothesize that lizards will form clusters of several species, since parthenogenetic female lizards are supposed to be less aggressive than sexual females (Tarkhnishvili et al., 2010), and asexual popula- tions have been reported to attain higher densities than sexual ones in similar habitats (Darevsky, 1967). As we do not expect much behavioural interference between species, parthenogens will be present in almost all clus- ters due to their low intraspecific aggressiveness and high population density (Tarkhnishvili et al., 2010). (3) To determine if habitat is a segregating factor among species, given differential habitat selection among species has been reported for Armenia (Arakelyan et al., 2011) with D. valentini tending to occupy meadows and grassland scattered with rocks, D. unisexualis steep rocky exposures, and D. armeniaca being intermediate in habi- tat use. MATERIALS AND METHODS Study area The study area was located near the village of Kuchak (Armenia; 44.385 N, 40.532 W, ca. 1940 m a.s.l.; Fig. 1) at the foothills of Mount Aragats. The study area includes several lon- gitudinal rocky outcrops alternating with grasslands and bushes (for a general view of the landscape see Figure 151 in Arakelyan et al., 2011). These outcrops are composed by accumulations of big rock boulders, reaching an approximate altitude of 1955 m a.s.l. in the highest point. Sampling was performed around the highest outcrops (0.34 ha; Fig. 1). Previous surveys had identi- fied high density of lizards in the study area. Species community composition The lizard community was composed of three species: one sexual (Darevskia valentini) and two asexual (D. armeniaca, D. unisexualis), as well as two hybrid forms (D. valentini/D. arme- niaca, D. valentini/D. unisexualis). In this locality hybridisation between sexual and asexual species is frequent, producing both diploid and polyploid hybrids (Danielyan et al., 2008). Individu- als were first determined at species level using external charac- teristics according to Darevsky (1967), Danielyan et al. (2008), and Arakelyan et al. (2011) and then corroborated by microsat- ellite analysis (Freitas et al., 2016a). Surveys We performed intensive surveys across the study area dur- ing three consecutive days (1-3 June 2011), coinciding with the reproductive period (Arakelyan et al., 2011). We concentrated sampling effort within a short time period to prevent pool- ing spatial locations shifted in time as expected from dispersal mediated by social interactions or with seasonal changes on home ranges (Boudjemadi et al., 1999; Galoyan, 2013). Each survey took around 8 hours covering the whole study area (Fig. 1). We surveyed all outcrops inside the study area. Therefore, each zone of the study area was visited only once. Lizards were also captured once to prevent pseudo-replication, we used tail- removal for parallel genetic analyses (see below) as individual mark. We recorded the position of each lizard with a profes- sional GPS unit (Trimble GeoExplorer, 2008 HX), with a preci- sion of 50 cm after post-processing. Data collection and lizard capturing We created a GPS data dictionary with Trimble GPS Path- finder office software v 5.0, transferring it posteriorly to the GPS unit. For all the observed lizards we recorded species, size class, sex; plant cover (0-25, 25-50, 50-75, 75-100%); and plant height (top, middle, down). Two team members (NS and EGM) walked randomly through the study area capturing lizards with a noose (García-Muñoz and Sillero, 2010). MAC measured SVL with a calliper to the nearest 0.01 mm and took pictures of each individual for confirmation of species identifications. Finally, EA recorded the exact location of the individual with the GPS unit as well as introduced all the data inside the GPS dictionary. In the end, we released each lizard in the exact capture site. The tail tip of each lizard was collected and kept for later genetic analyses, in order to confirm species determinations (Freitas et al., 2016a). Global clustering analysis We applied several tests of spatial statistics to describe the distribution pattern of the lizards. First, we analysed the dis- tance threshold of clustering for all the species together. Subse- quently, we grouped species by reproductive mode (partheno- gens: Darevskia armeniaca and D. unisexualis; and sexual indi- viduals: D. valentini and hybrids). For this, we used the Ripley’s K distance function (Bivand et al., 2008; Ripley, 1976; Rogerson, 2001), which measures the distribution of pairwise distances among events. The Ripley’s K function was calculated using the envelope function of the package “spatstat” (Baddeley and Turner, 2005) of the R software (R Team, 2014). In addition, a complete spatial randomness (CSR) point process with the same estimated intensity in the study area was simulated (999 repli- cates) and compared with the empirical values of Ripley’s K, to check whether the empirical function is contained inside. Determination of topological clusters Many methods have been proposed to determine clus- ters in a cloud of points (Bivand et al., 2008; Rogerson, 2001). What is considered a cluster, depends on the size of the study 158 Neftalí Sillero et alii area and a threshold distance (Sillero and Gonçalves-Seco, 2014). Multiple solutions are possible to define clusters inside a cloud of points, depending on the distance threshold select- ed, i.e. the distance where any cluster point is farther from any point outside the cluster. In order to avoid subjective solutions, this threshold distance must be determined statistically. Reli- able solutions are distance functions like the K function (Rip- ley, 1976) or the Nearest Neighbor Index (NNI; Clark and Evans, 1954). Every pair of points separated by a distance below the threshold distance is supposed to belong to the same clus- ter. In our study case, we used the Delaunay’s triangulation to identify spatially the clusters of lizards’ locations using the expected mean distance between neighbours provided by the NNI as statistical threshold. The Delaunay’s triangulation is a very well-known mathematical method, where for a given set P of discrete points in a plane, a triangulation is defined that no point in P is inside the circumcircle of any triangle in the plane. The expected distance provided by the NNI determines a clus- ter when the mean nearest neighbour distance is lower than the expected nearest neighbour distance. We selected the Delaunay triangles with lines shorter than the expected nearest neighbour distance (Clark and Evans, 1954). The points inside the selected Delaunay triangles were considered clustered. This analysis was performed in QGIS 2.0. Spatial segregation We measured the spatial segregation among species in two different ways. First, we calculated the degree of over- Fig. 1. Study area and records distribution. A: The study area was located near the village of Kuchak (Armenia) at the foothills of Mount Aragats. B: The lizard community is composed by one sexual species Darevskia valentini, two parthenogens (D. armeniaca and D. unisexu- alis) and the hybrids between the sexual and the asexual species. 159Spatial structure of a lizard community lap between species pairs. We calculated buffers with a radius equal to the expected nearest neighbour distance (Clark and Evans, 1954). We expect that species sharing space will have a high degree of overlap, while those spatially segregated will have a low degree of overlap. The overlaps were calculated with the Intersect function of QGIS 2.8. And second, we tested if males and females used differently habitats by means of log- linear models of the frequencies of both sexes and reproduction modes (asexual and sexual) in plant cover and height. RESULTS In the surveys we found a total of 149 lizards (Table 1 and Fig. 1): 101 Darevskia armeniaca, three D. uni- sexualis, 24 D. valentini, and 21 triploid hybrids (two D. armeniaca – D. valentini, and 19 D. unisexualis – D. valentini). There were fewer females of D. valentini (six) in comparison with hybrid females (13; Table 1 and Fig. 1). However, we found 18 males of D. valentini and only eight hybrid males (Table 1 and Fig. 1). Ripley’s K indicated that all species presented a clus- tered distribution, either together or grouped by repro- duction mode (parthenogenetic and sexual individuals; Fig. 2). We identified 11 clusters located in the north and in the south of the study area, with two clusters in the mid- dle (Fig. 3). D. armeniaca was the main species inside the clusters (Table 2). The clusters were composed of one to three species, with at least one parthenogen or hybrid participating (Table 2). Nevertheless, D. unisexualis never participated in a cluster (Table 2). The species pairs with the lowest overlap always included D. unisexualis. In fact, there was not overlap between D. unisexualis and hybrids of D. armeniaca/D. valentini. The pair of species overlapping the most was D. armeniaca and D. valentini (Table 3). Females and males used similar plant heights (χ2 = 0.411, P = 0.873; Table 4); both used areas with intermediate plant cover more often than expected by chance (χ2 = 8.451, P = 0.014; Table 4). Lizards with both types of reproduction were more fre- quent at middle height and in areas with intermediate plant cover (respectively: χ2 = 1.946, P = 0.378; χ2 = 6.197, P = 0.045; Table 4). When considering sex and reproduc- tion mode, all individuals were associated to middle plant heights (χ2 = 2.485, P = 0.672; Table 4), and used inter- mediate plant cover more often than expected by chance (χ2 = 9.543, P = 0.044; Table 4). DISCUSSION As predicted, species were not distributed randomly or regularly in the space but presented a clustered dis- tribution, either together or separately, as expected if resources within the study area were not randomly dis- tributed (Kwiatkowski and Sullivan, 2002). Indeed, since Kuchak area is composed by longitudinal rock outcrops alternating with grasslands and bushes, refuges and basking sites can be considered the main constraints for lizards. In fact, other studies on lizards’ communities showed similar results (Sillero and Gonçalves-Seco, 2014; Sillero and Gomes, 2016). Local clusters were composed of one to three species. As predicted, parthenogens (except Darevskia unisexu- alis) or their hybrids were present in all clusters probably due to their lower intraspecific aggressiveness (Galoyan, 2013) and high abundance (Tarkhnishvili et al., 2010). Particularly, D. armeniaca, the most abundant species in Kuchak, entered in all clusters. Conversely, D. unisexualis did not enter in any cluster, likely because of its low pres- ence in Kuchak (only three individuals recorded). Asexu- al females are supposed to be less aggressive than sexual females (Tarkhnishvili et al., 2010; Galoyan, 2013) and asexual populations have been reported to attain higher densities than sexual ones in similar habitats (Darevsky, 1967). It is important to highlight here that D. valentini Table 1. List of species detected and number of records per species, sex, and age. Species Female Male Adult Subadult Juvenile Adult Subadult Juvenile D. armeniaca 96 2 3 D. unisexualis 3 D. valentini 6 17 1 Hybrid D. arm -D. val 2 Hybrid D. uni- D. val 9 1 1 6 1 1 Total Result 116 3 4 23 2 1 160 Neftalí Sillero et alii females seem to be in minority in Kuchak, while hybrid females are more abundant. This pattern was also found by Danielyan et al. (2008), Sillero et al. (2016) and Car- retero et al. (2018) in the same site in different years. Females and males were concentrated in areas with medium plant cover. We were not able to confirm that D. valentini occupies ground habitats, i.e. meadows and grassland as described in general for Armenia (Arakelyan et al., 2011). As reported previously, sexual species (as well as parthenogens) were located mainly in habitats of middle height, which do not correspond to ground habi- Fig. 2. Ripley’s K plots of all records together and grouped by reproduction modes (parthenogens: Darevskia armeniaca and D. unisexualis; and sexual individuals: D. valentini and hybrids). The continuous line is the observed function of the species records; the dashed line is the theoretical function of a complete spatial randomness (CSR) point process; and the grey shadow is the lower and higher limits of the CSR point process after 999 replications. If the observed function is above the CSR limits, the point process is considered as clustered; if it is below the limits, as regular; if it is between the limits, as random. Fig. 3. Distribution of clusters identified with Delaunay triangula- tion and the expected nearest neighbour distance (see methods for more details). Numbers refer to cluster numbers in Table 2. Table 2. Number of species records per cluster. A cluster is a set of points where the distance to any point inside the cluster is farther from any other point outside the cluster. Cluster distance was deter- mined using the expected nearest neighbour distance (20 m). See methods for more details. Column numbers refer to cluster num- bers in Figure 3. Species 0 1 2 3 4 5 6 7 8 9 10 Total D. armeniaca 2 3 23 2 3 4 3 3 5 1 5 54 D. unisexualis 0 D. valentini 6 1 1 1 1 10 Hybrid D. arm – D. val 1 1 2 Hybrid D. uni – D. val 2 1 1 2 6 Total 3 3 32 3 5 4 5 3 6 3 5 72 161Spatial structure of a lizard community tats (Arakelyan et al., 2011). Distance analyses showed D. armeniaca and D. valentini were the species with a higher degree of overlap. This was expected since the first spe- cies is present in all habitats across the area. In contrast, D. unisexualis was included only in the clusters with the lowest overlaps, probably because of its low presence in Kuchak. As we stated above, the low abundance of this species was mostly responsible for its absence in clusters. These results seem to confirm that the Kuchak communi- ty acts like a sexual population of a single species (Sillero et al., 2016), even if strongly biased in sex ratio (Carret- ero et al., 2018). This is corroborated by the indirect evi- dence from inguinal scars in females which indicate that copulation attempts between species are as frequent as within species in this community (Carretero et al., 2018). The low density of D. valentini females strongly supports this conclusion. D valentini females are scarce likely due to genetic incompatibilities (Haldane’s rule) and parthe- nogens (and hybrid females) may be replacing them even for sexual interactions (Sillero et al., 2016). On the other hand, the species pair with the lowest overlap was con- stituted by both types of hybrids, likely because they are scarce and tend to behave like normal sexual species. Local spatial segregation by habitat or competition has been also related to clustered distribution patterns (Underwood and Chapman, 1996), with different degrees of intensity (Moody et al., 1997). Habitat is the main seg- regating factor in several communities of reptiles (Jones and Droge, 1980; Mellado, 1980; Scali and Zuffi, 1994). Micro-habitat selection promotes spatial segregation in lizards (Ortega and Barbault, 1982): juveniles of Anolis aeneus occupy open habitats instead of forests to avoid predation by A. richardi (Stamps, 1983a, 1983b). Spa- tial segregation in birds can be caused by competition between species (Moody et al., 1997). Plants segregate due to competition (Phillips and MacMahon, 1981; Haase et al., 1996; Getzin et al., 2006; Gray and He, 2009) and habitat selection (Schenk et al., 2003). Overall, spatial statistics offer new insights to inter- pret the spatial structure of species communities. By hav- ing a better statistical support, we were able to interpret how and why species segregate locally in space. This could be completed by a habitat segregation analysis as a continuous component of the environment once geo- graphical information of habitats will be made available for Armenia. Although some spatial statistic methods require data with homogeneous intensity, the cluster- ing and overlapping analyses applied here do not require this assumption as they are topographical distance-based Table 4. Number of individuals per plant height (down, middle, top) and plant cover (0-25, 25-50, 50-75, 75-100%), grouped by sex as well as sex and reproduction mode. Height Plant Cover % Down Middle Top Total 0-25 25-50 50-75 Total Sex Female 24 74 25 123 32 86 23 123 Male 6 16 4 26 1 22 3 26 Total 30 90 29 149 33 90 26 149 Sex/Rep Mode Sexual Female 6 10 3 19 5 12 2 19 Sexual Male 6 16 4 26 1 22 3 26 Asexual Female 18 64 22 104 27 56 21 104 Total 30 90 29 149 33 90 26 149 Table 3. Spatial segregation by pairs of species. Values are ranked from lowest to the highest degree of overlap. Species pairs Overlap (m2) D. unix × H D. arm 0.00 D. uni × H D. uni 1034.96 D. uni × D. val 1143.84 D. val × H D. arm 1236.06 H D. arm × H D. uni 2158.25 D. arm × H D. arm 2472.13 D. arm × D. uni 2650.51 D. val × H D. uni 8852.00 D. arm × H D. uni 11716.96 D. arm × D. val 13852.21 D. arm: Darevskia armeniaca; D. uni: D. unisexualis; D. val: D. valentini; H D. arm: Hybrid D. armeniaca-D. valentini; H D. uni: Hybrid D. unisexualis-D. valentini. 162 Neftalí Sillero et alii methods. As such, they are independent of the type of intensity distribution. Therefore, these methods perform better than standard ones when the sample size is low and the intensity is heterogeneous. Then, studies of spa- tial biology can be more frequent and we will have a bet- ter insight on questions such as species segregation and habitat use of species communities. ACKNOWLEDGMENTS NS was supported by a post-doctoral grant (SFRH/ BPD/26666/2006) and research contract (IF2013) from Fundação para a Ciência e Tecnologia (FCT, Portu- gal) and MAC is supported by project This research was supported by the FCT projects FCOMP-01-0124-FED- ER-007062, PTDC/BIA-BEC/102280/2008, FCOMP-01- 0124-FEDER-008929, PTDC/BIA-BEC/101256/2008, by the project “Biodiversity, Ecology and Global Change” co-financed by North Portugal Regional Operational Pro- gramme 2007/2013 (ON.2 ¨C O Novo Norte), under the National Strategic Reference Framework (NSRF), through the European Regional Development Fund (ERDF) and by the project “Preserving Armenian biodiversity: Joint Portuguese ¨C Armenian program for training in mod- ern conservation biology.” of Gulbenkian Foundation (Portugal). Research was approved by Yerevan State Uni- versity with permit nº 0606-433. REFERENCES Arakelyan, M., Danielyan, F., Corti, C., Sindaco, R., Levinton, A. 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