Xavier Santos
email: xsantos1@ub.edu

José Manuel Poquet

Ecological succession and habitat attributes affect the postfire response of a Mediterranean reptile community

Keywords: Reptiles, Postfire response, Habitat selection, Land use, Mediterranean basin

Wildfires are recognized as natural disturbances that have shaped landscape structure and ecosystem composition in many regions of the world. As ectotherms, many Mediterranean reptiles are expected to benefit from the thermal quality of open areas created by fires. However, not all the reptile species respond positively to this pattern. We have explored the response to fire of a Mediterranean reptile community in a protected area of the northeastern Iberian Peninsula. We visually searched for reptiles at 102 sites, including unburnt, recently burnt (2003), and old burnt (1985)(1986) localities. The number of reptiles and species richness was higher at burnt sites, and both were related to several variables of the habitat structure. Accordingly, between the two most common species in recently burnt sites, Podarcis hispanica declined in old fire habitats whereas Psammodromus algirus did not. Snakes did not differ between burnt and unburnt areas, although the ambush predator viper Vipera latastei was found more frequently in unburnt habitats. Our results imply that there are different succession trajectories for Mediterranean reptile species according to their habitat preferences, life history traits, and dietary specialization. The study area has been drastically human-altered in the last 100 years by agriculture, pine reforestation, agricultural abandonment, and wildfires. These land use changes drastically alter the vegetation cover, favoring some reptiles and damaging others, and finally can promote local extinctions of sensitive species to habitat shifts.

Introduction

The Mediterranean basin is widely recognized as one of the biodiversity hotspots in the world [START_REF] Myers | Biodiversity hotspots for conservation priorities[END_REF]. Nevertheless, this region has been altered by human activities over the centuries [START_REF] Bottema | Man's role in the shaping of the eastern Mediterranean landscape[END_REF][START_REF] Blondel | Biology and wildlife of the Mediterranean region[END_REF]. In this sense, the Iberian Peninsula has undergone drastic habitat transformations (e.g., urbanization, land abandonment, intensive agriculture, forestry, and fires) within small spatial scales and time periods [START_REF] Lloret | Wildfires and landscape patterns in the Eastern Iberian Peninsula[END_REF]. All these activities have wreaked habitat transformation, fragmentation, and loss, affecting at least 15% of all endemic animal and plant species, currently threatened with extinction (Brooks et al. 2002). Wildfires are common natural perturbations in the Mediterranean region [START_REF] Moreno | The role of fire in Mediterranean-type ecosystems[END_REF][START_REF] Rundel | Landscape disturbance in Mediterranean-type ecosystems: an overview[END_REF][START_REF] Trabaud | Fire and biological processes[END_REF], and human activities have increased their frequency and extent along the twentieth century (Lloret 2004). Wildfires impact animal communities by causing mortality directly [START_REF] Wilson | Fire effects on vertebrate fauna and implications for fire management and conservation[END_REF][START_REF] Whelan | The ecology of fire[END_REF]) as well as indirectly by changes in postfire habitat structure [START_REF] Wilson | Fire effects on vertebrate fauna and implications for fire management and conservation[END_REF][START_REF] Whelan | The ecology of fire[END_REF][START_REF] Brooks | Alien plants and fire in desert tortoise (Gopherus agassizii) habitat of the Mojave and Colorado deserts[END_REF]. These changes have ecological consequences, in terms of

Communicated by C. Gortázar

Electronic supplementary material The online version of this article (doi:10.1007/s10344-010-0387-8) contains supplementary material, which is available to authorized users.

changing the thermal microclimate [START_REF] Hurlbert | Fire and litter effects in undisturbed bluestem prairie in Kansas[END_REF][START_REF] Rice | Causes of decreases in productivity in an undisturbed tallgrass prairie[END_REF], exposure to predators, food availability [START_REF] Evans | Fire as a natural disturbance to grasshopper assemblages of tallgrass prairie[END_REF][START_REF] Kaufman | Small mammals and grassland fires[END_REF], and reproduction timing [START_REF] Lillywhite | Perching behavior of Sceloporus occidentalis in recently burned chaparral[END_REF][START_REF] Withgott | Elaphe obsoleta obsoleta. Response to fire[END_REF][START_REF] Cavitt | Fire and a tall grass prairie reptile community: effects on relative abundance and seasonal activity[END_REF].

In forest habitats, wildfire promotes the occurrence of new open areas and consequently facilitates the recolonization of open-space species [START_REF] Herrando | Does fire increase the spatial heterogeneity of bird communities in Mediterranean landscapes?[END_REF][START_REF] Santos | Recolonization of a burned Mediterranean area by terrestrial gastropods[END_REF]. Several ectothermal species take advantage of postfire conditions, colonizing new suitable thermal environments [START_REF] Huey | Physiological consequences of habitat selection[END_REF], hence promoting a priori positive fire responses. This positive response has been observed in some reptile communities (e.g., [START_REF] Pianka | Long-term changes in the lizard assemblages in the Great Victoria Desert[END_REF][START_REF] Rugiero | Effects of small-scale fires on the populations of three lizard species in Rome[END_REF]. However, [START_REF] Caughley | Effect of fire on the reptile fauna of mallee[END_REF] and [START_REF] Driscoll | How many common reptile species are fire specialists? A replicated natural experiment highlights the predictive weakness of a fire succession model[END_REF] reported that the response of reptiles to fire is not homogeneous within a single community. These authors recognized different succession trajectories for reptile species in Australian burnt areas, during the vegetation structure recovery. Some species rise in abundance just after fire whereas others need of many years for their recovery. Postfire changes in canopy and vegetation density succession can also be involved in local reptile extinction [START_REF] Ballinger | Path to extinction: impact of vegetation changes on lizard populations on Arapaho Prairie in the Nebraska Sand hills[END_REF][START_REF] Jäggi | Overgrowing forest as a possible cause for the local extinction of Vipera aspis in the northern Swiss Jua Mountains[END_REF][START_REF] Webb | Canopy removal restores habitat quality for an endangered snake in a fire suppressed landscape[END_REF]. These species-specific responses are related to habitat attributes and other environmental factors that vary across the postfire succession, favoring or harming species according to their requirements [START_REF] Rugiero | Effects of small-scale fires on the populations of three lizard species in Rome[END_REF].

The analyses of reptile responses to fire are informative for the conservation of these communities, poorly addressed in the Mediterranean region. The goal of our study is to examine the short-term response of a Mediterranean reptile community after a fire in terms of species richness and number of reptiles. The study has been conducted in a protected area affected by a big fire in 2003. We have sampled burnt and adjacent unburnt control sites to detect reptile species loss and gain after fire. Furthermore, for the two most common species, the objective has been to evaluate their responses to fire according to their habitat requirements. For these species, we also have compared their relative abundances in recent and old burnt sites (24 years after the fire) to analyze their postfire successional trajectories.

Material and methods

Study area

The study area is located inside the Sant Llorenç del Munt i l'Obac Natural Park, located in the NE Iberian Peninsula (Fig. 1). This is a 14,000-ha protected area characterized by a conglomerate landscape with Holm oak forest and Mediterranean shrubs, partially substituted by pine forest in peripheral areas of the park. The natural park has a long history of fires (667 fires registered between 1965 and 2003); however, the largest fire occurred in August 2003, when 4,500 ha on the eastern edge of the park were burnt (Fig. 1, zone C). Furthermore, in the western edge of the park, two big fires burnt in [START_REF] Caughley | Effect of fire on the reptile fauna of mallee[END_REF]1986 (Fig. 1, zones A andB).

The reptile community in the Natural Park has been recorded by numerous visits made by park rangers and local herpetologists. Its reptile checklist has been reported and updated in several publications [START_REF] Llorente | Atlas dels amfibis i rèptils de Catalunya i Andorra[END_REF][START_REF] Pleguezuelos | Atlas y libro rojo de los Anfibios y Reptiles de España[END_REF] and is available in 10×10 km UTM grid cells. Thirteen reptile species have been recorded in the park: one chelonian, six lizards, and six snakes.

Censuses methods

We made reptile censuses at 102 sites (Fig. 1) distributed in four habitat categories: (1) unburnt sites in Holm oak forests (n=17), (2) unburnt sites in pine forests (n=17), (3) old burnt sites (fires in 1985 or 1986, n=8), and (4) new burnt sites (fire in 2003, n=60). Prior to the fires, the majority of burnt sites were pine forests with Holm oak understory. These categories were selected to respond to the questions addressed in this work. We split unburnt sites in Holm oak and pine categories as these are the predominant forests in the Natural Park.

We recorded reptiles by two complementary methods: (1) reptile sightings during surveys searching for active specimens or those hidden inside vegetation or refuges. We surveyed each site twice, in spring and autumn 2007 during sunny and hot days, and each visit lasted 30 min. Reptiles were surveyed in an area of approximately 200-m diameter around the center of the sampling site. In each 200-m buffer, surveys were done in a zigzagging way in order to reduce resightings. Furthermore, in spring, we found mainly reproductive specimens whereas in autumn we often found juveniles. For this reason, the potential bias in the number of reptiles observed per site by resighting the same animals was much reduced. (2) At each sampling site, we located five pitfalls in a lineal transect separated 10 m from each other. Pitfalls were plastic containers of 10-cm diameter and 15-cm depth that effectively trapped lizards. Pitfalls were opened for 15 days every sampling period (spring and autumn) and checked every 2-3 days to report and release all reptiles trapped.

We also registered the macrohabitat (the area where reptiles were recorded) and microhabitat (the exact location where reptiles were recorded) of all the reptile specimens seen. Macrohabitat classes were described according to the presence of forest vs open sites; then, we defined the following classes: forest interior, forest edge, rocky area, burnt forest, and burnt forest edge. Microhabitat classes were grass, shrub, bare ground, and refuge (i.e., stone, dead trunk, and burnt branches).

Because of the sampling method described above, we found few snakes. For this reason, we also searched snakes at road trails within the park. Roads in unburnt and burnt areas were checked daily to collect dead snakes. Road trails were divided in 1-km stretches to compare statistically the number of snakes seen between unburnt and burnt areas.

We characterized habitat structure of the sampling sites by recording several vegetation and ground cover variables along a 50-m transect placed in the center of the site. The extent of several vegetation types (Holm oak, pine, oak, shrub, and grass) and ground cover variables (litter, refuges, bare ground, and wood) were recorded at points 50 cm apart along that transect. Thus, we recorded 100 points that characterized the abundance of vegetation and ground cover types at each site. We selected these variables due to their influence on the abundance and diversity of reptile communities [START_REF] Ribeiro | Biodiversity and land uses: is agriculture the biggest threat in reptiles' assemblages?[END_REF][START_REF] Márquez-Ferrando | Recovering the reptile community after the mine-tailing accident of Aznalcollar (SW Spain)[END_REF].

Statistical procedures

Ground cover and vegetation variables were used to characterize habitat differences among sampling sites. We performed a nonmetric multidimensional scaling (NMDS) with the Bray-Curtis similarity measure to relate such habitat characteristics to the presence of fires (old and recent fires), as well as to unburnt forests. The NMDS is a robust nonparametric ordination technique that avoids the assumption of linear relationships among variables and allows the use of a wide range of data types and similarity measures [START_REF] Mccune | Analysis of ecological communities. MjM software design[END_REF]. In this case, only the relative distances between objects in the ordination are relevant to the interpretation of the underlying patterns [START_REF] Quinn | Experimental design and data analysis for biologists[END_REF]. Thus, our sampling sites with similar habitat characteristics will be arranged close to one another within the NMDS plot, whereas sites with different habitat characteristics will be arranged separately. We used the software PC-Ord v5.14 [START_REF] Mccune | PC-ORD. Multivariate analysis of ecological data[END_REF] and its autopilot routine to conduct this analysis. We performed several general linear model (GLM) to explore whether there were significant differences in species richness and number of reptiles according to the four habitat categories (Holm oak, pine, old burnt, and new burnt) and park zones (A, B, and C in Fig. 1). The latter factor was considered because of the clustered sampling selection due to the spatial distribution of old and new fires in the park (Fig. 1).

After differentiating between burnt (old and recent fires) and unburnt sites (types of forests) throughout their habitat attributes, we performed multiple regressions to detect the weightiest attributes for richness and number of reptiles. Similarly, we developed multiple regressions for the two most common species in the study area (the Spanish wall lizard Podarcis hispanica and the large Psammodromus, Psammodromus algirus). Previously, ground cover and vegetation variables were explored in order to detect and remove those much correlated variables (correlation coefficient r≥0.8). Afterwards, the best regression model in each case was selected following the best subset approach implemented in the STATISTICA v.7.1 software (Statsoft 2005). This approach avoids problems that stepwise methods present [START_REF] Whittingham | Why do we still use stepwise modelling in ecology and behaviour?[END_REF]) and allows the selection of the best regression model by means of several information criterions [START_REF] Burnham | Model selection and multimodel inference: a practical information-theoretic approach[END_REF].

Stepwise procedures explore a small subset of all possible regression models. In this sense, the order of entry (or deletion) of predictor variables and the number of candidate variables used can affect the final model selection. Partial F tests of individual predictors are used for variable inclusion and removing rules of the regression model. Thus, they can lead to biases in parameters, overfitting, and incorrect significance [START_REF] Whittingham | Why do we still use stepwise modelling in ecology and behaviour?[END_REF]. We utilized the second-order Akaike's information criterion (AICc) to select the best regression model among all possible combinations of predictor variables [START_REF] Burnham | Model selection and multimodel inference: a practical information-theoretic approach[END_REF]. This measure is recommended for situations where the sample size (n) compared to the number of parameters (k) is small (n/k<40). Due to our unbalanced design (i.e., unequal number of sampling sites between burnt and unburnt sites), we performed all GLM analyses (analyses of variance (ANOVAs) and multiple regressions) calculating the corresponding sums of squares with the type III method [START_REF] Quinn | Experimental design and data analysis for biologists[END_REF].

We used log-linear analyses to test the differences in the macrohabitat and microhabitat use by the two most common species (P. hispanica and P. algirus) in the study area. Log-linear analysis is a statistical procedure that tests the association between several categorical variables in a multidimensional contingency table. The algorithm used generates several models to test interactions between all variables and selects the least complex model that fit the data. Once the models have been chosen, the goodness of fit is evaluated by the maximum likelihood ratio chisquared that compares whether the expected cell frequencies under the model significantly differ from the observed cell frequencies (i.e., in a good model, p will not be significant). The results are interpreted by regarding the odds ratio values among categories in the expected values of the marginal tables. GLM and log-linear analyses were performed with the STATISTICA v.7.1 software (Statsoft 2005).

The spatial distribution of the burnt and unburnt sites was constrained by the location of the old and recent fires, as well as by the presence of Holm oak and pine forests. The spatial pattern of species richness and total number of reptiles were explored by a distance-based autocorrelation analysis performed with Passage ver. 1.1 [START_REF] Rosenberg | Passage I[END_REF]). We constructed 25 distance classes of unequal length, setting constant the number of site pairs (n=200) being correlated. We performed a correlogram for the species richness and total number of reptiles, and spatial classes were defined by progressive distance between pairs of sites. Moran's I coefficients of spatial autocorrelation was calculated for each distance class and the significance level achieved by Monte Carlo method with 2,000 permutations. The significance of autocorrelation coefficients was corrected by a Bonferroni procedure due to the lack of independence of the distance classes (see [START_REF] Sánchez-Zapata | Land use changes and raptor conservation in steppe habitats of Eastern Kazakhstan[END_REF].

Results

During our field sampling and road trips, we found specimens of 12 out of 13 species previously recorded in the park (Table 1). The only undetected species was the Spanish terrapin Mauremys leprosa, since the sampling design was not adequate to see such reptiles as this chelonian inhabiting water bodies. Among lizards, only two species, P. hispanica and P. algirus, can be considered common in the Natural Park, although the ocellated lizard Timon lepidus has been found commonly at burnt sites.

The two-dimensional ordination given by the NMDS analysis (13.11% stress level) showed clear differences among burnt and unburnt sampling sites (Fig. 2). The first NMDS axis was positively correlated with the abundance of bare ground (r=0.84) and negatively correlated with the abundance of litter (r=-0.82) and pines (r=-0.76). On the other hand, the second NMDS axis was highly correlated with the abundance of Holm oaks (r=0.90) and litter (r= 0.87). Thus, most of burnt sites were located on the positive axis 1, recently burnt sites being the most concentrated. Unburnt sites were widespread along the axis 1 negative side, with a clear gradient from pine to Holm oak forest sites along axis 2 (Fig. 2).

The total number of reptiles and species richness showed significant differences between habitat categories (total number of reptiles: F 3, 96 =15.59, p<0.00001; species richness: F 3, 96 = 9.61, p =0.00001). Scheffé post hoc comparisons indicated that differences were between burnt and unburnt sites (p <0.05). Furthermore, there were marginal differences for species richness between old and recently burnt sites (p=0.06) although there were no differences for the number of reptiles (Fig. 3). In contrast, the GLM did not find differences between the three zones for the number of reptiles and species seen per site. This result suggests that, although the sampling was clustered by the location of the fires, differences were not related to the spatial distribution of the sites.

We found significant differences in the number of reptiles seen or trapped among the four site categories (visual, ANOVA F 3, 98 =13.90, p<0.00001; trapped, F 3, 98 = 4.14, p=0.008). Scheffé post hoc comparisons indicated in both sampling methods that the number of reptiles was higher in burnt than in unburnt sites. We did not find spatial autocorrelation of the total number of reptiles seen per site as there were no significant Moran's I coefficients for low-distance classes (Electronic Supplementary Material Table S1 and Figure S1). In contrast, we find spatial autocorrelation of the species richness as the closest sites (distances between sites up to 816 m) showed significant positive Moran's I coefficients (Electronic Supplementary Material Table S2 and Figure S2).

The best regression model for total number of reptiles seen (AICc = 213.57) showed that, among all vegetation and ground cover variables, pine, litter, and wood had significant effects. These three variables explained 37% of the variation of the total number of animals (number of reptiles=5.46-0.25 pine-0.32 litter+0.26 wood, F 3, 98 = 21.06, p<0.001, r 2 =0.37). On the other hand, the best regression model for species richness (AICc=-52.78) showed that litter and grass had significant negative effects on the total number of species, explaining 29% of its variation (species richness=2.28-0.53 litter-0.24 grass, F 2, 99 =21.97, p<0.001, r 2 =0.29).

One of two most common reptile species P. hispanica declined from recent to old burnt sites (student t test, t= 3.02, df=66, p=0.004) whereas P. algirus increased (t= -6.67, df=66, p<0.00001; Table 1). These two lizard species presented different requirements regarding the vegetation composition and ground cover structure. The best regression model for P. hispanica (AICc=170.01) showed its abundance to be positively determined by ground cover structures: refuges, bare ground, and wood (P. hispanica=-0.77+0.30 refuges+0.20 bare ground+0.44 wood, F 3, 98 =26.46, p<0.001). These variables explained 43% of P. hispanica variation (r 2 =0.43). On the other hand, although the best regression model for P. algirus (AICc= 123.2; P. algirus=1.91-0.27 pine+0.24 shrub-0.17 refuges, F 3, 98 =6.76, p<0.001, r 2 =0.15) involved one ground cover variable (refuges), this had no significant effect on P. algirus abundance (F 1, 98 = 3.41, p =0.068). Those variables that mainly determine P. algirus abundance were two vegetation composition variables (pine F 1, 98 =7.38, p=0.008; shrub F 1, 98 =6.14, p=0.015).

The log-linear analysis showed significant interactions among macrohabitat types, the presence of the two commonest species (P. hispanica and P. algirus), and the time since the last fire occurred (final model maximum likelihood ratio chi-squared, χ 2 = 3.12, p = 0.93). The highest odds ratio score (odds ratio>2) of two-variable marginal tables showed that P. algirus preferred forest-interior and forest-edge macrohabitats. Similarly, log-linear analysis also showed significant interactions, taking into account microhabitat types (final model maximum likelihood ratio chi-squared, χ 2 =2.71, p= 0.84). The highest odds ratio scores (odds ratio >2) of the two-variable marginal tables showed that P. algirus preferred grass and shrub microhabitats, and P. hispanica preferred refuges.

In agreement to the log-linear analyses, the percentage of P. hispanica and P. algirus recorded in different macrohabitats showed interspecific differences at unburnt sites, i.e., forested habitats for P. algirus and rocky habitats for P. hispanica (Fig. 4a). In contrast, differences were lower at burnt sites, probably due to the simplification of the habitat. The microhabitat preferences of P. algirus and P. hispanica in burnt and unburnt sites were clearly different and evidenced their ecological requirements: P. algirus selected shrub whereas P. hispanica selected refuges (Fig. 4b).

We found 57 snakes of six species, 19 in burnt and 38 in unburnt localities, combining samplings and road trail records (Table 1). The five colubrid species apparently inhabited both areas, although the small samples sizes preclude statistical comparisons. In contrast, the only viper in the park, the Lataste's viper Vipera latastei was found almost only in unburnt localities. Considering only the number of snakes found in 42 stretches of 1 km long in burnt and unburnt areas surveyed, we found no differences in the number of snakes (unburnt 23 transects, burnt nine transects, Mann-Whitney U test U =94.5, p=0.70).

Discussion

This study presents several pieces of evidence in favor of the variable postfire response of the Mediterranean reptile community studied, some species increasing in burnt (P. algirus) or only in recently burnt areas (P. hispanica) and others decreasing (V. latastei). These results may be informative for conservation issues and habitat restoration programs for reptiles in Mediterranean areas. Overall, there is an increase of reptiles in burnt localities, in agreement with other works that have demonstrated enhanced reptile populations in burnt habitats (e.g., [START_REF] Bury | Wildfire, fuel reduction, and herpetofaunas across diverse landscape mosaics in northwestern forests[END_REF]. Burnt and unburnt habitats differ in terms of habitat structure and availability of open areas (Fig. 2), and thus the large number of reptiles found at burnt sites should be related to the quality of the habitat (see also [START_REF] Valentine | Effects of weed-management burning on reptile assemblages in Australian tropical savannas[END_REF]. The higher number of reptiles collected in pitfalls at burnt sites can be caused by their increased mobility on open areas. However, differences in the number of reptiles were observed with both sampling methods (visual trials and pitfalls), thus sustaining the statement that the number of reptiles increased in burnt pine forests.

The extent of litter negatively affects species richness, and this result should reflect the general difficulty of reptiles to thermoregulate inside a dense canopy [START_REF] Huey | Physiological consequences of habitat selection[END_REF]. Our results are compatible with the thermal dependence hypothesis for reptiles as their richness [START_REF] Moreno-Rueda | The relative influence of climate, environmental heterogeneity, and human population on the distribution of vertebrate species richness in south-eastern Spain[END_REF] and distribution [START_REF] Aragón | The contribution of contemporary climate to ectothermic and endothermic vertebrate distributions in a glacial refuge[END_REF]) are strongly associated to temperature in the Mediterranean region. However, this does not apply in other parts of the world different to the Mediterranean biome, particularly tropical and desert areas [START_REF] Kearney | The potential for behavioral thermoregulation to buffer "cold-blooded" animals against climate warming[END_REF]. The extent of grass also negatively affected species richness. In other words, within burnt sites, those with a high extent of grass have lesser reptile species than those without grass. An expansion of short-lived seeding plant species such as grass is a typical trend in early postfire succession (Lloret 2004); however, the commonest reptiles in the park, P. hispanica and P. algirus, did not make use of grassy habitats either at burnt (Fig. 4) nor unburnt sites [START_REF] Pérez-Mellado | Estructura de una taxocenosis de Lacertidae (Sauria, Reptilia) del Sistema Central[END_REF]. This pattern is in fact general for Mediterranean areas where only a few species are grassy vegetation specialists (except skinks of the genus Chalcides, [START_REF] Rugiero | Effects of small-scale fires on the populations of three lizard species in Rome[END_REF].

All reptile species living in the Natural Park do not follow the same postfire response, this conclusion confirming previous findings in Australia [START_REF] Caughley | Effect of fire on the reptile fauna of mallee[END_REF][START_REF] Driscoll | How many common reptile species are fire specialists? A replicated natural experiment highlights the predictive weakness of a fire succession model[END_REF] and USA [START_REF] Perry | Reptile and amphibian responses to restoration of fire-maintained pine woodlands[END_REF]). Several of our results support this conclusion:

1. All lizards previously reported in the Natural Park were detected during this survey. However, within lizards, there were also interspecific differences in the successful colonization of burnt areas. For example, the Moorish gecko Tarentola mauritanica did not colonize burnt habitats regardless of the presence of adequate microhabitats [START_REF] Hódar | Foraging mode of the Moorish gecko Tarentola mauritanica in an arid environment: inferences from abiotic setting, prey availability and dietary composition[END_REF]. Species living inside the forest (i.e., the slow worm Anguis fragilis) was not recorded at burnt sites although was frequently killed on roads crossing unburnt areas within the Natural Park (authors, personal observation). 2. Despite of the thermoregulatory quality of burnt habitats for reptiles, the number of snakes seen did not differ between roads crossing adjacent burnt and unburnt areas. This result could be related to some ecological life history constraints of snakes that did not affect lizards. Specialists in some ecological traits and low reproductive output, snakes are particularly sensitive to anthropogenic habitat disturbance (see a review in [START_REF] Webb | Ecological characteristics of a threatened snake species, Hoplocephalus bungaroides (Serpentes, Elapidae)[END_REF]. Although many ecological features of snakes are unknown, many species combine several traits such as low fecundity, retarded sexual maturity, and small population size, making them vulnerable to extinction [START_REF] Webb | What make a species vulnerable to extinction? Comparative life-history traits of two sympatric snakes[END_REF]. Within snakes, specialist species in the habitat use are more threatened than generalist species [START_REF] Segura | Specialist and generalist species in habitat use: implications for conservation assessment in snakes[END_REF], and ambush predators snakes are more commonly threatened than active foragers [START_REF] Reed | Lying in wait for extinction: ecological correlates of conservation status among Australian elapid snakes[END_REF]. Within the snake assemblage in the Natural Park, V. latastei is the only ambush predator and the most ecological specialist [START_REF] Santos | Inferring conservation status with ecological modelling techniques and GIS: an application with Vipera latastei in the Iberian Peninsula[END_REF], factors that probably would explain why it was found more frequently in unburnt than in burnt habitats (Table 1).

The low numbers of snake observations suggest the need of snake-specific capture techniques in future studies to analyze explicitly the response of these species to fire. 3. Between the two most common species in the Natural Park, there were also clear differences in their postfire trajectories. Both lizards are good short-term colonizers of burnt areas, with dense populations at some recently burnt sites (Santos, personal observation). However, in old fire sites, P. hispanica clearly declined whereas P. algirus did not. The low numbers of P hispanica in old burnt sites could be a location effect as the sampling design is spatially clustered due to the distribution of old and recent fires (Fig. 1). However, GLM analyses did not find differences in species richness between eastern and western areas, whereas old and recent fires marginally did. These differences between the commonest reptiles are similar to those reported in other postfire succession studies [START_REF] Pianka | Long-term changes in the lizard assemblages in the Great Victoria Desert[END_REF][START_REF] Letnic | The responses of small mammals and lizards to post-fire succession and rainfall in arid Australia[END_REF][START_REF] Driscoll | How many common reptile species are fire specialists? A replicated natural experiment highlights the predictive weakness of a fire succession model[END_REF].

In our case, P. hispanica and P. algirus differed at macrohabitat and microhabitat scales and also with regard to burnt and unburnt sites. At unburnt sites, P. hispanica and P. algirus are known to be spatially segregated at both macrohabitat and microhabitat scales [START_REF] Pérez-Mellado | Estructura de una taxocenosis de Lacertidae (Sauria, Reptilia) del Sistema Central[END_REF]. In recent fire sites, despite a simplification of the habitat structure, both species are abundant and remain spatially segregated, especially in their microhabitat preferences (Fig. 4b). In old fire sites (25 years after fire), P. hispanica becomes uncommon probably because of vegetation recovery whereas P. algirus remains abundant. This conclusion reflects that habitat quality is ephemeral for species with special habitat requirements as P. hispanica (i.e., specialists of first stages in the ecological succession, [START_REF] Buddle | Arthropod responses to harvesting and wildfire: implications for emulation of natural disturbance in forest management[END_REF]. In fire-suppressed landscapes, vegetation density and cover increase and habitat heterogeneity declines, negatively affecting biodiversity in several groups [START_REF] Conway | Effect of forest fire suppression on buff-breasted flycatchers[END_REF][START_REF] Moreno-Rueda | The relative influence of climate, environmental heterogeneity, and human population on the distribution of vertebrate species richness in south-eastern Spain[END_REF] including reptiles [START_REF] Webb | Canopy removal restores habitat quality for an endangered snake in a fire suppressed landscape[END_REF].

In addition to the increase of canopy cover during postfire succession, the availability of shelter sites underlies the successful recovery of reptile populations at burnt habitats. In fact, several examples of habitat restoration for reptiles are based on the addition of artificial refuges in degraded habitats (e.g., [START_REF] Zappalorti | Artificial refugia as a habitat improvement strategy for snake conservation[END_REF][START_REF] Castilla | Artificial egg-laying sites for lizards: a conservation strategy[END_REF][START_REF] Webb | Paving the way for habitat restoration: can artificial rocks restore degrade habitats of endangered reptiles?[END_REF][START_REF] Márquez-Ferrando | Recovering the reptile community after the mine-tailing accident of Aznalcollar (SW Spain)[END_REF]. The increment of vegetation during succession closes shelters or makes them unattractive to many species, and the scarcity of refuges negatively affects reptiles at the population and community levels [START_REF] Goode | Habitat destruction by collectors associated with decreased abundance of rock-dwelling lizards[END_REF]. Accordingly, in our study, P. hispanica was common under refuges at burnt sites (60% of records, Fig. 4b) whereas only 35% of observations in unburnt sites were due to the reduction of these microhabitats in unburnt habitats. In burnt sites with scarcity of shelters (rocks and walls), P. hispanica was seen frequently on dead trees where they have not been removed (Santos, personal observation). In consequence, logging can impact the viability of species such as P. hispanica, as it has been documented in other species [START_REF] Lindenmayer | Salvage harvesting policies after natural disturbance[END_REF][START_REF] Kavanagh | Vertebrate species assemblages and species sensitivity to logging in the forests of north-eastern New South Wales[END_REF][START_REF] Herrando | Postfire forest management and Mediterranean birds: the importance of the logging remnants[END_REF]). Nevertheless, logging is the most widespread practice in the Mediterranean Basin [START_REF] Haim | The effect of fire treatments on the community composition of small mammals in a postfire pine forest[END_REF].

The Mediterranean Basin has been shaped by humans for millennia [START_REF] Blondel | Biology and wildlife of the Mediterranean region[END_REF]. Several pastoral and agricultural activities have sustained a diverse array of biological communities which have developed a strong preference for seminatural habitats [START_REF] Moreira | Modelling the impact of agricultural abandonment and wildfires on vertebrate diversity in Mediterranean Europe[END_REF]. For this reason, postfire response of a Mediterranean reptile community should be analyzed in light of the historical land use changes made in the area studied. In the early twentieth century, the study area was dominated by vineyards with very scarce vegetation (Electronic Supplementary Materials Figure S3a). After the Phylloxera plague, fields were abandoned and naturally replaced by pine forest and Holm oak undergrowth (Fig. S3b). Agricultural abandonment in recent decades has completed the forest recovery of the area, although the fire of 2003 altered the landscape structure again (Fig. S3c). It is likely that this historical transformation of the land use and vegetation cover had selectively affected species with high sensitivity to local habitat changes such as Mediterranean reptiles [START_REF] Ribeiro | Biodiversity and land uses: is agriculture the biggest threat in reptiles' assemblages?[END_REF]. Then, this factor should be taken into account to analyze the response of reptiles to disturbances in human-altered habitats by comparing historical reptile records and land changes in long-term surveyed areas.

Fig. 1

 1 Fig. 1 Location of the study area in the NE Iberian Peninsula and the 2003 wildfire. Symbols represent the location of the 102 sampling sites as old fires (open circle), recent fire (solid circle), unburnt Holm oak (solid triangle), and unburnt pine (stars). Some unburnt sites, being inside the fire area, are unburnt isolated stands. The black line delimitates the Sant Llorenç del Munt i l'Obac Natural Park, and gray areas are the extent of the main fires of 1985 (A), 1986 (B), and 2003 (C)

Fig. 3

 3 Fig.3NMDS two-dimensional ordination of sampling sites where the symbol size is proportional to the size of the total number of species (up) and the total number of animals (down). Dashed line separates burnt (right) and unburnt (left) sites

Fig. 4

 4 Fig. 4 Percentage of P. hispanica and P. algirus in a macrohabitat and b microhabitat types in burnt and unburnt sites

Eur J Wildl Res (2010) 56:895-905

Acknowledgments We thank R. Márquez, R. Ribeiro, and D. Salvans for field assistance and people of the Sant Llorenç del Munt i l'Obac Natural Park for logistic assistance. M. Casals provided old photographs of study area. David Nesbitt is acknowledged for language editing. X.S. was supported by a Beatriu de Pinós postdoctoral grant from the Government of Catalonia (BP-B1 10211).