Emiliano Mori, Mattia Menchetti, Matteo Cantini, Giacomo Bruni, Giacomo Santini & Sandro Bertolino (2017) Twenty years’ monitoring of a population of Italian crested newts Triturus carnifex: strong site fidelity and shifting population structure in response to restoration, Ethology Ecology & Evolution, 29: 460-473
DOI: 10.1080/03949370.2016.1236040
Twenty years monitoring of a population of Italian crested newts Triturus carnifex: strong site fidelity and shifting population structure in response to restoration
EMILIANO MORI1*, MATTIA MENCHETTI2, MATTEO CANTINI2, GIACOMO BRUNI2, GIACOMO SANTINI2 and SANDRO BERTOLINO3
1. Dipartimento di Scienze della Vita, Università di Siena, Via P.A. Mattioli 4, 53100, Siena, Italy. E-mail: moriemiliano@tiscali.it
2. Dipartimento di Biologia, Università di Firenze, Via Madonna del Piano 6, 50019 Sesto Fiorentino (Firenze), Italy;
3. DISAFA, Università di Torino, Largo Paolo Braccini 2, 10095 Grugliasco (Torino), Italy. 4. *corresponding author: Emiliano Mori, Department of Life Sciences, University of Siena, Via
P.A. Mattioli 4, 53100, Siena, Italy. E-mail: moriemiliano@tiscali.it
Human-induced environmental alterations, e.g. the introduction of alien species and the application of management practices, together with climatic change, represent the main threat to worldwide amphibian conservation. Long-term monitoring programs are mandatory to monitor the status of amphibian populations in changing landscapes and climatic conditions. In this study, we showed the population dynamic of the Italian crested newts Triturus carnifex living in four artificial ponds in Central Italy over a 20-years period. Adult newts were recognized through a capture-mark-recapture protocol, involving the analysis of belly patterns. The first best population model showed a constant newt survival among years and a complete recapture rate; the second supported model showed a sex-dependent survival, with slightly higher values for males with respect to females and corroborate a complete recapture rate. A high philopatry occurred: we observed less than 10% of individuals dispersing from a birth site to other ponds. In 20 years of continuous monitoring, the population of Italian crested newt increased. The removal of goldfish Carassius auratus from one of the ponds in 2010 allowed adult newts to overwinter within the pond and to have two reproductive periods, with overwintering larvae after the second spawning.
KEY WORDS: Alien species impacts; amphibian decline; belly pattern; capture-mark-recapture; Carassius auratus; long term monitoring.
Running Head: long-term monitoring of Triturus carnifex
Introduction
In the Sixth Global Biodiversity Crisis Era, amphibians are the most endangered vertebrate group, mainly because of their low vagility, narrow habitat tolerance level and vulnerability to human-mediated environmental alterations (Cushman 2006). Anthropogenic factors, including habitat loss, introduction of non-native species and pathogens, and human-mediated climate change pose serious threats (Houlahan et al. 2000; Van Buskirk 2005; Eigenbrod et al. 2008).
Water uptake, alteration, and pollution of small streams may be particularly harmful, depriving amphibians of the elective environments for their reproduction (Heatwole 2013; Vitt & Caldwell 2014). A form of habitat alteration includes the introduction of alien fish species: these
introductions are a well-documented and widespread threat to amphibians (Kats & Ferrer 2003). Introduced fish, particularly Salmonids, i.e. the brown trout Salmo trutta and the brook trout
Salvelinus fontinalis, represent effective predators of eggs, larvae and paedomorphic stages of
amphibians (Stebbins & Cohen 1995; Denoel et al. 2005), as well as of adult individuals (Tiberti & von Hardenberg 2012). Herbivorous fish, e.g. Cyprinids, widely released in small ponds, may also affect amphibian - mainly Urodels - breeding success (Richardson et al. 1995; Zambrano et al. 1998) by damaging the eggs, as well as the vegetation on which they are laid through grazing (Richardson et al. 1995). Furthermore, herbivorous and omnivorous fish may prey on macroinvertebrates (Roy 1992; Kloskowski 2009), which build up the staple of the diet of most amphibian species (Fasola & Canova 1992; Dutra & Callisto 2005). Wounds on adult newts exerted by Cyprinids through biting may also increase the success of pathogen attacks (Cantini 2014). Despite the abundance of scientific literature on this topic, many studies have been carried out in extreme ecosystems, e.g. Alpine lakes (Bradford et al. 1998; Tiberti & van Hardenberg 2012; Magnea et al. 2013), with little attend paid to Mediterranean ecosystems.
Climatic change alters the water temperature and availability throughout the year, possibly exerting a severe impact on amphibian fitness (Blaustein et al. 2010). For instance, the local increase of environmental temperatures may affect the sex-ratio at birth within populations (Wallace et al. 1999; Matsuba et al. 2008). In several species of reptiles and amphibians, environmental sex determination may occur (Wallace et al. 1999; Janzen & Phillips 2006). In these cases, environmental conditions (e.g. water temperature and pH) experienced during early development are the main factors determining the sex (Wallace et al. 1999; Matsuba et al. 2008). Increases in the number of males within a population of crested newts may be related to an increase of temperature during egg-laying period (Wallace et al. 1999). The alteration of natural sex-ratio may in turn affect reproduction and recruitment success, thus compromising the viability and the persistence of animal populations (Redfield et al. 1978; Janzen 1994; Lips 1998). Long-term studies can be used to monitor the status of local populations and the potential population-level effects of recent land-use changes and shifting climatic conditions (Arntzen & Teunis 1993).
Although landscape and environmental changes may rapidly occur, thus promoting rapid abandonment of unsuitable sites (Edgar & Bird 2006), long term data may help in understanding how different species respond to these pressures, since they cover a broad scale of time, which captures any recent land use changes. Up to now, few studies on time-series analysis have been applied to amphibian populations (Salvidio 2007): long term monitoring programs may be difficult and expensive (Cagnacci et al. 2012). Monitoring requires repeated and standardised observations of abundance over long time, using methods enabling the detection of changes in numbers (Elzinga et al. 2001).
Among amphibians, the Italian crested newt Triturus carnifex can be used as a model species for these studies, as it presents a defined belly pattern, which rapidly allows individual recognition (Hängstrom 1973; Arntzen & Teunis 1993). Although the number of spots on the ventral part of this newt species may increase over time, changes are gradual and do not hinder the individual recognition, if captures occur over consecutive years, or more than once a year (Biancardi & Di Cerbo 2010). Furthermore, changes are uncommon in adult individuals (i.e. > 3-4 years old: Arntzen & Teunis 1993). The reproductive season of Italian crested newt starts between February and April, when individuals reach the ponds where they remain until late summer (Andreone & Giacoma 1989; Sindaco et al. 2006). Males arrive at water approximately 1-2 weeks before females, and they defend a selected territory through cloacal secretions (Arntzen 2002). Migration from the aquatic to the terrestrial environment occurs at the end of the breeding season (Schabetsberger et al. 2004), generally following a straight line recognized through olfactory and visual information (Jehle & Arntzen 2000; Sinsch & Kirst 2016). Migrations occur mainly at night, when environmental temperatures are the lowest, and relative humidity the highest (Schabetsberger et al. 2004). Females travel the longest distances, although it may depend on the habitat matrix around the ponds (Joly et al. 2001; Schabetsberger et al. 2004). Where winter temperatures do not go below
0°C, Italian crested newts may overwinter within the same ponds where they breed (Giacoma 1988; Fasola & Canova 1992). Among Urodeles, which generally show a high philopatry, crested newts can switch their breeding site allegiance when new areas suitable for reproduction become available (Beebee 1996). This pioneer behaviour (Arntzen & Teunis 1993) makes the Italian crested newt a key species to study the recolonization of ponds by native taxa after alien fish removal programs.
In this work we report the results of 20 years of monitoring of a population of Italian crested newt in a hilly area of Central Italy through a capture-mark-recapture protocol. We expected that (i) the eradication of a small population of goldfish Carassius auratus may have resulted in a population increase and that (ii) the little local increase of environmental temperature (Mori & Plebani 2012) may have not yet altered the local population dynamics.
Materials and methods
Study area
The study area is composed by four ponds located in a hilly area in Southern Tuscany (“Poggi di Prata”, Province of Grosseto; 70 ha., 520-780 m a.s.l.). The average annual rainfall is approximately 850-900 mm, with occasional episodes of snowfall. The average annual temperature is about 14°C, with average thermal excursions during the year of about 20°C (Cantini et al. 2013; Fig. 1)
The Italian crested newt is the most abundant amphibian species in the study site after the common toad Bufo bufo. Its presence is recorded in all the four artificial ponds (hereafter referred to as Pond A-D) present within the study area (Cantini et al. 2013). Pond A (Fonte Canali: 43.116° N, 10.983° E) is located in a woodland glade; Pond B and Pond C (respectively, Fonte dei Poveri and Pozza di Bosco 43.098° N, 10.990° E) are separated by a dirt road and are located at the border of a chestnut wood. Twelve to fifteen individuals of goldfish (1 ind./0.13 m3) were present in Pond C between 1981 and 2010, when they were removed. Pond D (La Pilina) is located outside in a private vegetable garden immediately outside the village of Prata. Each pond was built up by 1-6 artificial cement tanks. Main features of each site are summarized in Tab. 1. Biological communities have been previously analysed and described and were similar among the four sites (Mori & Giovani 2012; Cantini et al. 2013; Mori et al. 2013). All the ponds were characterized by the presence of non-frozen water throughout the year and three of them, Pond A, Pond B and Pond C, are formed by spring water. By contrast, Pond D was mainly fed by rainwater used for irrigation; once a year (in September), the pond was emptied and cleaned by the owners of the vegetable garden. This management practice was also conducted, in the same month, for Pond B and Pond C until 2001-2002, and involved the partial removal of water vegetation and substrate.
The water conductivity (s/cm) was measured through a conductivity-meter FA33 (FASTTECH, Seregno, Italy). Water chemical features were measured through SERA® tests for aquariology and were constant throughout the year (2014: Tab. 2). General water hardness (GH) and carbonate hardness (KH) showed low values. All the sites were characterized by a low concentration (mg/l) of chlorine and by the near absence of nitrates and nitrites. The pH was nearly neutral at the four sites, and the dissolved oxygen showed higher values in Pond A, B and C with respect to tanks in Pond D (with the lowest values corresponding to late autumn, when the depth of the tanks reached its minimum). Given the small extension of the analyzed ponds and the small population size, we assume that all the Italian crested newts present within them were captured at each survey. The closest population of Italian crested newts was located about 6.6 kilometers away to the ponds (Cantini et al. 2013). Individuals of the research population have never been observed in this last place and vice versa (E. Mori unpubl. data).
Newts were caught once a month between 1994 and 2013 through a fishing net with telescopic handle, which allowed researchers to sample all the individuals present within each tank. Captured adult newts were measured (snout-vent length, hereafter SVL: Arntzen & Teunis 1993) through an electronic precision caliper and sexed. The number of larvae was not taken into account to avoid underestimation, as the presence of crevices along the walls of the ponds reduces the detectability of individuals smaller than 5 cm (Arntzen & Teunis 1993).
Ventral patterns were drawn by hand until 2004, then photographed through a digital compact camera (Canon Powershot A70). A comparison of images was conducted to verify the correspondence between the drawings and photos, and to allow the continuity in the individual identifications (Supplemental Material 1). Drawings of the patterns were conducted on a preprinted sheet with the outline of the newt. Newts were immobilized one by one on the bottom of a transparent box, with the ventral part downwards, to photograph (or to draw) their belly pattern. This procedure required the presence of at least two researchers. The individuals were then released within the same pond where they were captured. The time for manipulation and photograph never exceeded a minute (2-3, when patterns were drawn) and did not require anesthesia.
Age of adult animals was determined by adding up the years of recapture, and adding 2 years to the first year of recognition of a defined pattern (Arntzen & Teunis 1993). A subsample of individuals (N=5 females and N=5 males) underwent skeletochronology analyses, which confirmed the age calculated through capture-mark-recapture (Makovický et al. 2015).
Statistical analyses
We analysed population biometrics by comparing body measurements of males and females, to assess the occurrence of sexual-size dimorphism and if monitored newts reached normal dimensions when adult (i.e., 21 cm for females, 15 cm for males: Lanza & Campolmi 1991). We calculated medians and quartiles (1st Q - 3rd Q), instead of means and SD (Sokal & Rohlf 2012), as no measurement was normally distributed even after log10-transformation (Shapiro-Wilk normality test: W = 0.93, P = 0.02). Longevity was measured as the number of successive years of recapture plus 2 years, which were added to account for time to maturation. Thus, individual recognition was not possible for individuals younger than two years of age, which had not yet reached maturity (Arntzen & Teunis 1993). Inter-sexual differences were evaluated through the Student's t-test, as data were normally distributed (Shapiro-Wilk normality test: W = 0.97, P = 0.12: Sokal & Rohlf 2012). Usually, movements of crested newts follow straight lines (Jehle & Arntzen 2000). Thus, dispersal distances were calculated as the minimum straight line connecting the place where the individual was born and the place where it reproduces. Statistical comparisons between the distances traveled by males and females were made using the Mann-Whitney U-test (Shapiro-Wilk normality test: W = 0.91, P < 0.01). Analyses were conducted through the software R version 3.1.3 (www.cran.r-project.org), package Rcmdr (Fox 2005).
Environmental temperatures were taken from a local meteorological station (cf. Mori & Plebani 2012). A sex ratio (number of males/number of females) was calculated each year, then correlated to the mean environmental temperature during the breeding period of 2 years before (when individuals were estimated to be born: Arntzen & Teunis 1993), to assess whether increasing temperature affect the number of new males detected within this population each year. Analyses were conducted through the software R version 3.1.3 (www.cran.r-project.org), package Rcmdr (Fox 2005).
Mark–recapture techniques are used to generate robust estimates of population parameters. Collected data therefore were analyzed through the software MARK using a Cormack-Jolly-Seber live recapture model for open populations, which is the best one to estimate survival of reproducing populations with live re-encounters (White & Burnham 1999; Schwartz 2001; McClintock & White 2010). Candidate models were ranked according to the AICc score for small sample sizes. We used delta AICc (ΔAICc) and the Akaike weights (wi) to select the top supported models. The ΔAICc is
the difference between the AICc of a given model and the AICc of the highest ranked model. A
ΔAICc < 2 suggests a substantial evidence for the model (Burnham & Anderson 2002). The Akaike
weights indicate the probability that the model is the best of the whole set of candidate models. Analyses were performed with data from all the ponds pooled together, because we observed movements of individuals among sites.
We evaluated the growth pattern of males and females by building regression curves of SVL with respect to age (in months), following standard protocols (McCullagh & Nelder 1989; Arntzen 2000): the fit of each model was assessed using a polynomial regression procedure that compares the fit of the most complex equations and a simpler equation. The simplest regression which significantly increased the R2 value was retained. The analysis was performed in R version 3.1.3 (www.cran.r-project.org), using the Grofit package (Kahm et al. 2010).
Results
Overall, a total of 488 capture events occurred, consisting of 65 unique individuals (32 males and 33 females). Mean sex ratio (calculated each year) of the population was 1.27 ± 0.57. The ratio between males and females reversed during the study period: females dominated in the first years until 1999, but males were more abundant in the successive years (Fig. 2). The increase of males with respect to females was correlated to the increase of environmental temperature during the breeding period (R = 0.75; P < 0.001). No newt from other nearby monitored areas has been observed within the four sites. Thus, we suppose that all the individuals determined through the belly pattern were born within the study area. Newts were found in the water throughout the year, peaking during the spring (i.e., main reproductive season) and decreasing in winter. Wintering sites have been identified in 1-12 meters from the tank, under stones or stone walls, in shrubby areas or at the limits of deciduous woodlands.
On average, the maximum number of individuals was detected in May, the minimum in December (Fig. 4). If we exclude the few adult individuals which remained within the ponds throughout the year (n = 6), most males arrived in late February and left the ponds in late August. Females arrived later (second half of April) and left the ponds in late September. We also found that the first individuals to enter ponds were also the first to leave the ponds.
Between 1994 and 2013, the population showed a positive trend, which increased after 2011, when the eradication of goldfish occurred (Fig. 2). Tab. 3 shows the top five models ranked from the lowest AICc values. The first two models have a ΔAICc = 1.095, indicating that the first model was not convincingly the best model and the second one should be considered supported as well. Overall the two models have a wi of 0.734. The first model indicated a constant survival of newts
among years (Phi: 0.91, 95% CI = 0.87-0.93) and a complete and constant recapture rate (P = 1.0). The second supported model showed a sex-dependent survival, with slightly higher values in males (Phi: 0.92, 95% CI = 0.88-0.95) with respect to females (Phi: 0.89, 95% CI = 0.85-0.93), and a complete recapture rate (P = 1.0) as well.
The SVL of adult females (median value = 7.3 cm ; Q1-Q3: 6.8-7.5 cm) was significantly higher (Mann-Whitney U = 380.5 ; P < 0.001 ) than that of males (median value = 6.4 cm ; Q1-Q3: 5.9-6.6 cm) with a peak of 8.1 cm for females and 7.4 cm for males. No significant differences between the sexes for longevity (females: 9.4 ± 2.4 years; males: 8.8 ± 2.1 years; t = -1.21; P = 0.23) was observed. The maximum recorded longevity was 19 years for a female and 15 for a male. SVL increased with a cubic curve both in males (Fig. 4, R2 = 0.98, F
3,23 = 394.8, P < 0.01, P-value of increase in R2: P< 0.001) and females (R2 = 0.99, F
3,23 = 616.8, P < 0.01, P-value of increase in R2: P< 0.001). Males and females reach their maximum SVL at the same mean age, i.e. 40.22 ± 4.37 months for males and 40.77 ± 4.52 months for females (t = 0.4953; P = 0.62).
Dispersal movements from the native site were only observed for 8 adult males and 5 adult females; 76.92% of these movements were recorded between Pond B and Pond C after goldfish were eradicated. The maximum dispersal distance was 2039 linear meters, which was covered by
two males (between Pond A and Pond D, through Pond C). No significant difference in length of dispersal distance was observed between sexes (Mann-Whitney U = 20.00; P = 0.64).
Discussion
Over the 20 years of monitoring (1994-2013), the total population of Italian crested newts increased approximately 5 fold, with a peak in numbers occurring in 2013 (40 individuals). We suggest that the increase from 2011 might be the result of the removal of introduced goldfish at Pond C. This Asian fish has been introduced worldwide as an ornamental species (Takada et al. 2010), although yet its impact on native biodiversity is poorly known. It may reduce the quality of water, as it alters the zooplankton communities and promotes algal blooms (Roy 1992; Takada et al. 2010). This may in turn decrease the concentration of dissolved oxygen (Richardson et al. 1995), thus increasing the extinction rates of freshwater invertebrates (Innal 2011). All these changes may indirectly affect the survival of crested newts, whose diet is mainly composed by freshwater arthropods (Fasola & Canova 1992; Sindaco et al. 2006). When goldfish were present in Pond C of our study area, few adult crested newts occurred during the breeding season, and larvae and eggs were never observed. About 60% of these adult newts showed lesions to the tail or to the hind limb. Goldfish are reported to be the cause of fitness reduction in small newt species (e.g., Lissotriton
helveticus: Winandy et al. 2015), but this is the first evidence of its impact on a larger species. After
the removal of goldfish, no wounds were observed on any captured newts at Pond C. Since 2011, reproductive success was observed, which may lend support to our hypotheses regarding the effects of goldfish on the dynamics of this population.
Sex ratio per year within the study sites was always near 1, confirming the data published on other species of the same species complex (Arntzen & Teunis 1993). Although we found a significant correlation between sex ratio and temperature, our second-best model showed a higher survival for males. Thus, it seems likely that the increase in the number of males may be a result of increased temperatures. Long-term water temperature data from deployed loggers would be needed to state the effect of temperature dependent sexual determination in the alteration of sex ratio in our dataset.
Body size of captured individuals were comparable to those reported for this species by Lanza & Campolmi (1991). Adult females were about 11% longer than males, while no difference between sexes was detected on longevity and dispersal distances. Males and females reached the maximum SVL at the same age (around 3.3 years), thus confirming data on growth rates by Arntzen (2000). The Italian crested newt was observed to be a philopatric species, with a low rate of dispersal exerted by adults, as in the similar T. cristatus (Arntzen & Teunis 1993). The maximum distance traveled by two males was 2039 linear meters, which increases the previously reported value of traveled distances in this species by approximately 1.5 fold. This result also strongly supports the pioneer behavior that has been hypothesized for this species complex (Arntzen & Teunis 1993). The mean age of reproductive individuals per year was similar between males and females (about 9 years: Cantini 2014); longevity reached 19 years for a female, three years higher than the highest previously (Cvetkovic et al. 1996). Although no neotenic adult was observed, some crested newts were found inside the tanks throughout the year, even during winter and when snow cover was present on the ground. In similar studies, summer drought and/or winter ice periods were largely responsible for recruitment failures (Arntzen & Teunis 1993). In our study area, aquatic habitats were available throughout the year, thus allowing newts to remain within the ponds. However, most newts appeared to overwinter under the stones/stone walls located in the immediate surroundings (1-12 m) of each pond. Over 70% of individuals wintering within ponds (N = 12) were found in Pond C, but only after the removal of goldfish. This suggests that goldfish affected newt population structure and dynamics.
Accordingly, overwintering larvae have been only detected in this pond, where two reproductive events per year occurred in 2012 and 2013: one in early spring and the other in late summer/beginning of autumn. Individuals born in early October spent the whole winter in the larval
stage and completed their metamorphosis to the adult form at the beginning of the following spring, reaching body sizes up to 8.2 cm, tail included (Covaciu-Marcov & Cicort-Lucaciu 2009). Differently from the other sites, Pond C has a thicker substrate layer and a stone wall full of crevices, which may constitute a thermal refuge to newts during the coldest months, thus allowing the wintering of adults within the water and the second reproductive event. The muddy substrate also ensures an almost constant internal temperature throughout the year.
Other events which might have contributed to increase the Italian crested newt population in the study area include the avoidance of tank-cleaning procedures before the end of September and the reduction of water withdrawal from tanks where newts were present (especially in Pond B and Pond D).
Small and isolated populations, such as the one of Italian crested newts analyzed in our work, are particularly predisposed to extinction (Salvidio & Oneto 2008). Habitat fragmentation and loss lead to the degradation of breeding sites and ecological corridors, therefore being a major cause of the global amphibian population decline (Blaustein et al. 1994; Hecnar & M’Closkey 1996; Beebee 1997; Semlitsch & Bodie 1998). Constant field efforts, which include long-term monitoring programs, are necessary tools to understand amphibian population dynamics and to design effective population models for conservation practices (e.g. Jacobson et al. 2004; Pañella et al. 2010; Vergari & Dondini 2011). To finish, the population of Italian crested newt in Poggi di Prata seems to be still in a good conservation status. The preservation of the current status of aquatic sites (including the avoidance of alien fish release) and of the nearby terrestrial habitats should be maintained to allow the continuity of ranging movements among subpopulations.
Acknowledgements
Newts were captured with permissions by the Ministry of the Environment (prot. 0006222) and the Province of Grosseto (prot. 0030326), as well as the agreement by the National Institute for Environmental Research (ISPRA, prot. 0048780) and the Societas Herpetologica Italica (SHI, prot. 0047321). Authors thank Alice Giovani, Mattia Ricci, Lee Kats, Andrea Vannini and Michele Zago for their valuable help in the collection and analysis of data. Jan Willem Arntzen and Leonardo Ancillotto kindly provided us with useful suggestions and comments on the first draft of this manuscript. Vasco Sfondrini kindly took the time to read and correct English grammar and syntax, markedly improving the readability and the fluency of the manuscript. To finish, the comments of two anonymous referees improved greatly our manuscript. This work is dedicated to the bright memory of Enrico Romanazzi, who spent his research-life to promote conservation of amphibians in north-eastern Italy.
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Tables
Table 1. Main dimensional features of the ponds where the study was carried out. Linear distance
from the nearest pond is also reported.
Site Elevation (m a.s.l.) Tanks (N) Volume (m3) Length (cm) Width (cm) Depth (cm) Distance from the nearest pond (m)
Pond A 778 6 0.14 137 32 33 619 (Pond B)
Pond B 695 2 3.82 266 205 70 236 (Pond C)
Pond C 703 1 1.99 313 120 53 236 (Pond B)
Pond D 576 1 0.94 116 116 70 612 (Pond C)
Table 2. Mean annual values (± standard error) of water parameters for each pond: KH, carbonate
hardness; GH, general hardness.
Site Conductivity(s/cm) Chlorine(mg/l) Nitrates(mg/l) Nitrites(mg/l) Oxygen(mg/l) pH KH(°KH) GH(°GH)
Pond A 316.71 ± 83.87 0.85±0.05 0.75±0.50 0.50±0.25 4.15±0.82 7.58±0.38 5.32±1.74 12.91±3.23
Pond B 136.01 ± 33.07 0.80±0.05 0.25±0.25 0.25±0.25 4.40±1.17 6.45±0.27 3.82±1.06 7.55±2.33
Pond C 177.02 ± 42.51 0.70±0.05 0.25±0.25 0.25±0.25 4.30±0.95 6.49±0.62 4.41±1.45 8.59±3.46
Pond D 430.71 ± 70.38 0.90±0.30 0.75±0.50 0.50±0.25 3.48±1.69 7.50±0.63 6.91±1.81 13.73±2.49
Table 3. The first five selected models with the lowest AICc values, their Akaike weights (wi) and
other model parameters; in bold, the two models with the best support.
Models AICc ΔAIC wi Model
likelihood Parameters No. Deviance
Phi(constant) p(constant) 276.880 0.000 0.465 1.000 2 177.207
Phi(sex) p(constant) 277.976 1.095 0.269 0.578 3 176.275
Phi(constant) p(sex) 278.901 2.027 0.169 0.363 3 177.207
Phi(sex) p(sex) 280.012 3.132 0.907 0.209 4 176.275
Figure 2. Population dynamics of the Italian crested newt (males in light blue, females in red) in
four ponds in Southern Tuscany; population estimates are indicated by the continuous line, while dashed lines represent the 95% confidence interval.
Supplemental material
Figure 1S shows the reliability of the comparison between drawings (1994-2003) and photos (2004-2013) of the ventral patterns of Italian crested newts, which allowed the authors to continuously monitor individuals.
Figure 1S. Comparison between drawings and photos of crested newts: A) a female from Pond A;
