Abstract
Although Ablepharus kitaibelii and its subspecies are wide-spread, being distributed from the Carpathian Basin through the Balkans to Iraq, their habitat and environmental niche is poorly known. Ablepharus kitaibelii fitzingeri is almost entirely limited to the Carpathian Basin, and is amongst the most strictly protected and least known reptiles of Central and Eastern Europe. The main aim of our study was to determine habitat use preferences of different age groups of A. kitaibelii fitzingeri and Lacerta viridis. The occurrence of green lizard was determined by the abundance of refugia rather than by the naturalness of grasslands. The snake-eyed skink prefers semi-natural grasslands with abundant tussock-forming grass or sedge species, avoiding densely shrubby places. For the first time, we show that woodland mosaics lacking shrubs and temporary grasslands next to forest edges are important for the species. Microhabitat use by snake-eyed skink varies with age group; adults preferring shady edge zones rich in leaf litter and shadier grassland spots provided by woodland mosaics, whereas juveniles were found in natural, more open grasslands far from forest edges and in woodland mosaics with dense shrubby understory. Our results contribute to a better understanding of the ecological needs of A. kitaibelii fitzingeri. Our methodology could be adapted to other species and subspecies of Ablepharus. Based on our results, it is important to reconsider habitat management activities, which should not be limited to shrub control: the main goal should be the development of a diverse habitat structure.
Introduction
Habitat selection can be determined by a number of factors including thermal characteristics, food and the potential for mate acquisition as well as protection from predators (Huey, 1991; Downes and Shine, 1998; Downes, 2001). Through microhabitat selection within a specific habitat, these factors can define the optimal needs of organisms living in that specific environment (Huey et al., 1989; Kearney, 2001; Compton, Rhymer and McCollouhg, 2002). In reptiles temperature in environment often plays a significant role in habitat selection (Webb and Shine, 1998; Blouin-Demers and Weatherhead, 2001; Chruszcz and Barclay, 2002), because of their ectothermic nature (Huey and Slatkin, 1976; Huey, 1991; Chen, Cu and Xiang, 2003; Zhang and Ji, 2004). Also multiple factors influence need to be taken into account when trying to understand microhabitat selection of organisms. The need for optimal body temperature is unlikely to be the sole determinant of microhabitat selection (Quirt et al., 2006) and heterogeneity of thermal space is important (Sears, Michael and Angilletta, 2015). For example, sometimes the primary factor in habitat selection is the protection from predators (Shah et al., 2004) and under high level of predation the protection can be of greater importance than thermoregulation (Downes and Shine, 1998; Downes, 2001).
Thus, habitats are not selected randomly in a given area, but relate to the environmental requirements and the combination of factors affect microhabitat selection determining the distribution of a population (Brown and Orians, 1970; Krebs, 1978).
Several lizard species show a preference for particular habitat structure elements (Heatwole, 1977), so understanding these is essential to planning conservation measures.
Ablepharus kitaibelii (Bibron, Bory and St-Vincent, 1833) and its subspecies are very wide-spread, from the Carpathian Basin through the Balkans to Iraq. The habitat and environmental needs, as well as the reproductive biology, of A. kitaibelii are hardly known in Europe (Pasuljevič, 1965, 1976; Gasc et al., 1997). Previous researches have mostly focused on finding new localities (Harmos and Herczeg, 2003; Korsós et al., 2008).
Ablepharus kitaibelii fitzingeri (Mertens, 1952) is one of the most highly protected and probably also the least known reptile species of Hungary. In Europe it is listed on Annex IV of the Habitat Directive (European Commission 1992), and Appendix II of the Bern Convention (Council of Europe 1994). The biology of the fitzingeri subspecies, and also of the other members of the genus, has been poorly researched. This may be due to the rarity of A. kitaibelii fitzingeri and its secretive lifestyle or the fact that their habitats are hardly accessible. As there are no past studies of population densities and none are underway, changes can only be suspected on the basis of the fact that the subspecies can no longer be found at a number of sites where it was formerly known. This might suggest that this lizard is probably severely declining in Hungary (Herczeg et al., 2004). Previous studies mainly focused on the distribution of the subspecies (e.g.: Harmos and Herczeg, 2003; Herczeg et al., 2004; Korsós et al., 2008).
Ablepharus kitaibelii fitzingeri occurs only in the Carpathian Basin (Korsós, 2007), mainly in Hungary, and an understanding of habitat preference is an essential prerequisite for evidence-based conservation in the area. Examination of their ecological and habitat needs is important, as is the identification of factors threatening the populations’ survival such as potential predators, competitors and the impact of human activity. The fitzingeri subspecies mostly lives in quite isolated populations; probably due to its body size and way of life it is only able to colonise new habitats slowly (Korsós, 2007), and it may find it difficult to adapt to changed conditions. Its current distribution largely coincides with already protected areas or habitats meeting the criteria for protection. Previous studies (e.g.: Harmos and Herczeg, 2003; Herczeg et al., 2004; Korsós et al., 2008) of A. kitaibelii fitzingeri mainly concerned highland populations, most of which were relatively unthreatened compared to those in the lowland hills and plains, where sites are often isolated by farmland, highly fragmented and at risk of loss to cultivation.
In most habitats where A. kitaibelii fitzingeri occurs, it is found together with the Eastern green lizard Lacerta viridis (Laurenti, 1768) (Harmos and Herczeg, 2003). The daily activity and habitat use of both species are presumed to be very similar (Herczeg et al., 2007a). There are very few studies about the habitat use of the subspecies (Harmos and Herczeg, 2003; Herczeg et al., 2007a), but the habitat use of other Ablepharus species has been studied, providing a good basis to inform the direction of research (Pasuljevič, 1965, 1976; Georgios and Vassiliki, 2009; Szövényi and Jelic, 2011). For example Ablepharus budaki (Göcmen, Kumlutas and Tosunoglu, 1996) was mostly found in leaf litter and grass tussocks and was rarely detected near shrubs (Georgios and Vassiliki, 2009), while all the individuals of Ablepharus pannonicus, Fitzinger were collected amongst leaf litter and partially decomposed plant debris from Quercus spp. (Fathnia et al., 2009). A study of the lizard fauna of a Greek mountain area has shown that A. kitaibelii kitaibelii (Bibron and Bory, 1833) occured along with L. viridis and Podarcis muralis (Laurenti, 1768) and the presence of trees was extremely important for the snake-eyed skink, since it was found only in locations where a well-developed litter layer was formed by the leaves of deciduous trees and pine needles (Strijbosch, Helmer and Scholte, 1989). Finally, another study also draws attention to the importance of leaf litter for A. kitaibelii kitaibelii, since 55% of the observations were on this substrate (Ioannidis and Bousbouras, 1997).
The main aim of our study was to determine habitat use preferences of different age groups of A. kitaibelii fitzingeri and L. viridis in a Pannonian Quercus pubescens woodland and its grassland patches in Hungary. Secondly, we determined which and how habitat and environmental parameters affect the distribution of both species in the study area.
Finally, we wished to assess the applicability of our results for conservation interventions.
Material and methods
Study site and survey methods
Our survey was conducted in the grassland patches of a 155 ha fenced reserve within a >6400 ha forest located east of the town of Gödöllő in Pest County (WGS 84 coordinates are N 47.6007, E 19.4090). The study area is classified as Acer campestri-Quercetum roboris coenotaxa of a closed thermophilous Quercus pubescens forest (Fekete, 1961). This habitat type is named as Pannonian Quercus pubescens woods in the EUNIS habitat classification. This forest type contains field maple (Acer campestre) as well as other temperate woodland species such as hornbeam (Carpinus betulus). Other main tree species include Turkey oak (Quercus cerris) English oak (Quercus robur) and manna ash (Fraxinus ornus). Grassland patches have formed in this habitat which, due to its orientation and slope conditions, is hardly forested. In total, five fragments of grassland patches of 0.70 hectares can be found in the survey area.
We applied a widely-used observation-based method for the examination of the ecological needs of lizard species (Martín and Salvador, 1995). The range of habitat variables used during our work was adjusted to the behavioural, biological and lifestyle factors and specificities of the snake-eyed skink and green lizard. Wherever a snake-eyed skink or green lizard was detected, structural variables of the habitat were recorded in a 1 meter circle (3 m2) (Pernetta, Bell and Jones, 2005; Ross et al., 2008). We spent approximately 8 minutes on the recording of each sighting. We measured air temperature and air humidity 15 cm above ground level, recorded the percentage coverage of fallen deadwood on the ground, potential refuges and the percentage coverage of grass, the canopy of trees and shrubs. For temperature and air humidity measurements a Voltcraft HT200 (Voltcraft, Germany) was used.
The percentage coverage of potentially important plants for the given species were visually estimated (Drozd, 2010; Szövényi and Jelic, 2011) thus, the coverage of tussock-forming grass and sedge species (Carex, Festuca and Stipa species) was recorded separately from total coverage of grass. Due to the presumed similarities in the lifestyle of the snake-eyed skink to other skinks, environmental variables (such as leaf litter coverage and depth) identified in studies dealing with other terrestrial skink species were incorporated in our work (Pernetta, Bell and Jones, 2005; Ross et al., 2008). Field sampling took place during the active period of lizards, between 7:00 and 19:00 in spring, summer and autumn 2013. Lizards were surveyed by visual detection, observers moving slowly along pre-defined tracks. This method (Herczeg et al., 2007a) was complemented by adjusting our direction of movement to the position of the sun, taking care that the surveyor’s shadow did not fall on the examined spot, which would have risked disturbing the animals before they had been detected. The exact GPS coordinates of each individual were recorded using a Garmin Legend HCx. Data on the orientation of the habitat were not recorded separately, since all the grassland study areas were located on south-western slopes.
Statistical analyses
All microhabitat variables were included in a Principal Component Analysis (PCA) to reduce the microhabitat variables into a smaller number of factors which described the underlying dimensions of the data. All percentage variables were arcsine square-root transformed prior to inclusion in the PCA. Four PCs were extracted from the ten original variables according to the Kaiser’s criteria. To make the PCs biologically interpretable, we used Varimax initial factor rotation (Nie et al., 1975). On the basis of the Streiner and Norman (2000) critical value analysis, the minimum approved factor value was 0.289. Analysis of Variance (ANOVA) was used to find specific, interspecific and inter-age group differences in the PC scores, followed by the Least Significant Difference (LSD) test. LSD is basically a set of individual t-tests and computes the pooled standard deviation from all groups. Any difference larger than the LSD is considered a significant result. All statistics were calculated using IBM SPSS software (IBM Corporation, 2011).
Results
In a total of 23 field sampling days, we collected habitat information for 320: (n = 175 A. kitaibelii fitzingeri, n = 145 L. viridis). The Principal Component Analysis of the microhabitat data of the two species produced 4 principal components (PCs). The cumulative percentage of variance of these was 73.54 % (table 1). PC1 and PC2 explain the most cumulative % of variance, but PC3 and PC4 explain less variance thus we focused on results obtained only from PC1 and PC2 in the discussion.
Correlations of microhabitat variables with the first four PC scores after the Varimax rotation for A. kitaibelii fitzingeri and L. viridis using data from spring, summer and autumn. The minimum approved factor values (in bold) are according to Streiner and Norman (2000) critical value analysis.
PC1 was positively correlated with grass height, air humidity and temperature and with the coverage of tussock-forming grass and sedge species, but negatively correlated with leaf litter depth and coverage (table 1). Therefore, it showed a gradient from warm, humid, natural grasslands rich in tussock-forming grass species to edge-zones, forest edges and woodland mosaics rich in leaf litter.
PC2 showed a positive correlation with canopy coverage, leaf litter coverage and shrub coverage, but was negatively correlated with the coverage of tussock-forming grass species (table 1). Thus, it shows a gradient from shady scrub-dominated grasslands, forest edges and woodland mosaics rich in leaf litter to natural, open grasslands.
The third component was positively correlated with the coverage of tussock-forming grass and sedge species, but negatively correlated with secondary grasslands and grasslands lacking tussock-forming grass and sedge species (table 1). It showed a gradient from natural grasslands rich in leaf litter, and grassland edges located near shady forest edges and woodland mosaics, to open, secondary or disturbed grasslands, with transformed grasslands lacking tussock-forming grass or sedge species.
The fourth component showed positive correlation with the coverage of fallen tree trunks, bigger branches and shrubs but was negatively correlated with the coverage of tussock-forming grass and sedge species (table 1). This means that it showed a gradient from scrub habitats, rich in natural refugia, to open, natural grasslands (with high percentage of Festuca, Carex and Stipa spp.).
Mean PC scores ± SE of microhabitat selection in different age groups of Ablepharus kitaibelii fitzingeri and Lacerta viridis.
Citation: Amphibia-Reptilia 37, 2 (2016) ; 10.1163/15685381-00003039
ANOVAs identified significant difference between the two species and age groups (fig. 1; PC1: , ; PC2: , ; PC3: , ; PC4: , ).
In the first component, the habitat use of adult A. kitaibelii fitzingeri was different to that of their juveniles (LSD test: ) and to adult L. viridis (LSD test: ). Adult L. viridis also significantly differed in PC1 from juvenile A. kitaibelii fitzingeri (LSD test: ), while juvenile L. viridis showed a significant difference only from adult L. viridis (LSD test: ).
In PC2 and PC3, only the A. kitaibelii fitzingeri juvenile and L. viridis juvenile age group showed a significant difference (LSD test PC2: ; PC3: ).
In PC4, both age groups of A. kitaibelii fitzingeri showed a distinction from both age groups of L. viridis (LSD test: all ), while adult L. viridis significantly differed also from L. viridis juveniles (LSD test: all ), but the Ablepharus age groups were not significantly different from each other (LSD test: ).
Discussion
We found that adult A. kitaibelii fitzingeri avoided warm, humid, open grassland patches in spots with little canopy coverage. They typically used habitat patches rich in leaf litter, for example shady border zones and cooler, shadier grassland patches provided by woodland mosaics. As the fallen leaves of trees and shrubs heat up quicker in the early morning than other microhabitat elements (Martín, López and Cooper, 2003), this may be particularly beneficial for the snake-eyed skink. This can further nuance our current knowledge about the habitat use of the species (Herczeg et al., 2007a), since we now understand that it is not a species strictly tied to open grasslands but rather a species with a need for shrubs and trees providing shade and leaf litter in a given habitat. Therefore the habitat needs of A. kitaibelii fitzingeri are more complex than we previously thought (Herczeg et al., 2007a).
Lacerta viridis juveniles’ habitat choice is similar to that of adults: they occupy habitats right next to shrub patches and forest edges, while Ablepharus juveniles prefer natural leaf-litter rich grasslands and try to avoid scrub while the close proximity of shady forest edges and woodland mosaics are also important. In comparison juvenile green lizards, in the absence of refugia, can be detected on high-growth secondary grasslands, which contain a small proportion of low-growth, tussock-forming grass and sedge species (Festuca spp., Carex spp. and Stipa spp.). The habitat use of Ablepharus adults is highly similar to both L. viridis age groups. Due to its orientation, the habitat of the examined area is exposed to strong sunshine from early morning to late evening. Our results suggest that the most significant limiting factors for A. kitaibelii might be the proportion of shade-providing canopy and the availability of shelters. This finding may be linked to heat-bearing characteristics dependant on body size, since the smaller a lizard, the quicker it can overheat (Herczeg, Török and Korsós, 2007b). It has been shown that there is a strong overlap between the diurnal and seasonal activity of A. kitaibelii fitzingeri and the activity of L. viridis, although the snake-eyed skink showed minimal activity on grassland patches in the hottest and driest summer periods (Herczeg et al., 2007a). Several studies have shown that lizards with greater body size look for structural environmental and habitat elements which promote the attainment of appropriate body temperature (Herczeg et al., 2007a), but for many small terrestrial skink species passive thermoregulation has a greater influence (Ross et al., 2008).
Shrub patches, fallen tree branches and decaying tree trunks were the most characteristic refugia of L. viridis in the study area. Both age groups of A. kitaibelii fitzingeri preferred natural grasslands, but adult individuals also used the forest and woodland mosaics edge zones. They thus avoided patches occupied by adult green lizards, presumably as a predator-prey response, given documented predation by adult L. viridis on the smaller adult A. kitaibelii fitzingeri (Herczeg and Korsós, 2003; Herczeg et al., 2007a). Our personal field observations also support this view since we observed adult L. viridis predation on A. kitaibelii fitzingeri in the edge zones of habitat patches occupied by each species. This implies that snake-eyed skink under predation pressure does not take the most optimal place (Herczeg et al., 2007a) in the available space. This conforms with several studies which have proved that microhabitat selection is not determined only by thermoregulation needs, but also by the accessibility of protection from predators (e.g.: Shah et al., 2004). In some cases, species prefer suboptimal habitats, rather than endure intense predation pressure or strong interspecific conflicts (Downes, 2001). Open areas are beneficial in terms of thermoregulation (Bakken, 1989), but do not provide enough shelter for large lizard species (e.g.: L. viridis). When attacked by a ground or air predator, the snake-eyed skink usually seeks refuge under the grass tussocks; the high coverage of tussock-forming grass species is especially beneficial. In case of emergency it simply disappears under the grass tussocks and leaf litter, and digs into the soil (Arnold, Burton and Ovenden, 1978; Herczeg et al., 2007a). It is important for all reptiles to be in reach of basking places and shelter (Bennett, 1980; Carrascal et al., 1992), and for most species, this is much more important early in the morning, in the period of low movement performance (Van Damme et al., 1989; Carrascal et al., 1992).
Our examinations were carried out in a unique hilly habitat, and further developed our understanding of the distribution of the species, since it became obvious that not only larger grasslands (e.g.: Harmos and Herczeg, 2003; Herczeg et al., 2004; Korsós et al., 2008) can be suitable habitats, but also smaller grasslands interspersed by tree and scrub mosaics, as well as grassland patches located in woodlands, other habitat types could also be suitable for the species, thus studies on distribution could expand to new habitat types.
In conclusion the snake-eyed skink prefers semi-natural grasslands with abundant tussock-forming grass or sedge species, avoiding densely shrubby places. Woodland mosaics lacking shrubs and temporary grasslands next to forest edges are also important for the species. Adults preferring shady edge zones rich in leaf litter and shadier grassland spots provided by woodland mosaics, whereas juveniles were found in natural, more open grasslands far from forest edges and in woodland mosaics with dense shrubby understory.
Conservation recommendations
Based on the results of our study, we think it is important to reconsider the approach of habitat management activities designed for A. kitaibelii fitzingeri. Current activities only limited to shrub control, but the main goal should be the development of a diverse habitat structure. To reach this goal, we recommend the gradual opening up of shrubby understories beneath trees and dense scrub patches on grasslands in strongly overgrown habitats, thus minimising the risk of slope erosion and the spread of invasive plant species. Instead of scrub clearance, thinning should also be carried out in less strongly overgrown areas. In those areas that are already well-managed, in regenerated spots, or in habitats in good condition for other conservation objectives but lacking native trees we recommend the planting of oak (Quercus spp.) and ash (Fraxinus spp.) to form a diverse habitat mosaic. In places where pioneer large, competitive grassland species become dominant in the grassland structure, ideal grass height should be maintained by regular mowing or grazing, thereby encouraging the expansion of Carex, Festuca and Stipa species beneficial for A. kitaibelii fitzingeri. All grassland management work should be scheduled outside the vegetation period, by which the direct destruction and disturbance of the animals can be avoided, paying special attention to the fact that in case of favourable weather conditions, the snake-eyed skink can be active from early February till November.
Acknowledgements
This work was professionally supported by Amphibian and Reptile Conservation Group of MME Birdlife Hungary. Special thanks to Ádám Szabó for assisting with vegetation sampling and David O’Brien and Jeanette Hall from Scottish Natural Heritage for their helpful comments on the manuscript and for proof reading the English text. The lizards were collected under a permit issued by the National Inspectorate for Environment, Nature and Water. Permit number: 14/4751-9/2011.
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Footnotes
Associate Editor: M. Carretero.
