Nile Monitors (Varanus niloticus) have been established in Florida since the 1990s and are considered a high-risk invasive species. The ecology of this species in Florida, however, is poorly understood. We used trapping data from a city control program to examine the effects of daily weather conditions on probability of capturing Nile Monitors in live-animal traps. We originally collected trapping data by setting baited live-animal traps in terrestrial habitat along canals in Cape Coral, Florida, USA from July 2007 to December 2022. Traps were checked daily while they were deployed, and capture dates of Nile Monitors were recorded. Logistic regression analysis suggested that rainfall had a significant positive effect on probability of capture one day later but had significant negative effects on probability of capture on the same day and three days later. Chi-square tests indicated significant positive associations between presence of rainfall and capture occurrence one and two days later. These results may reflect optimal foraging strategies of Nile Monitors in Florida. We suspect that conditions following rainfall may result in increased movement and could consequently increase probability of capture.
.-Precise demographic data are needed to model population dynamics, design management and recovery strategies, and answer questions in ecology and evolution, but for many species, accurate information on age and frequency of reproduction is lacking. Using data from a 10-year capture-mark-recapture study, I describe demographic analyses of sympatric populations of three natricine snakes, Dekay's Brownsnakes (Storeria dekayi), Red-bellied Snakes (S. occipitomaculata), and Common Gartersnakes (Thamnophis sirtalis), focusing on age and frequency of reproduction. I examined cloacal smears from males for sperm and palped females for enlarged follicles and embryos to infer minimum size at maturity and used logistic regression to relate sperm positivity and gravidity to size. I determined minimum age of maturation and first reproduction from known-age von Bertalanffy growth equations. I estimated female reproductive frequency from reproductive histories, proportion gravid, and relationship between size and gravidity. Using this information, I constructed matrix projection models to compare the effect of accelerated or delayed reproduction on the population growth parameter, ). In all three species, a small proportion of females reproduced when just one year old but for most females, and for males, age of first reproduction was 2 years. Accelerating reproduction by a year resulted in rapid population growth (lambda = 1.08-1.18), and delaying reproduction resulted in rapid population decline (lambda= 0.86-0.91) relative to baseline (lambda= 1.00). Further quantification of demographic traits and associated trade-offs could improve population projection models and provide a clearer understanding of life history variation.
Species with broad distributions experience diverse environmental conditions and selective pressures across populations that can drive adaptive responses such as phenotypic plasticity and genetic differentiation. Vanzosaura (Gymnophthalmidae) is widely distributed across South America's open diagonal, occurring in the Cerrado, Caatinga, and Chaco regions of Brazil. We studied body size, sexual size dimorphism, reproduction, and diet in three Vanzosaura species from different ecosystems. Our goals were to evaluate the extent to which traits vary with environmental predictability and to test Boyce's hypothesis that body size is positively correlated with environmental stability. We predicted that species from the more climatically predictable Cerrado (V. rubricauda and V. savanicola) would show larger body size and seasonal reproduction whereas the Caatinga species (V. multiscutata) would exhibit smaller size and continuous reproduction. We found no significant dietary differences; all species consumed primarily Araneae, Orthoptera, and Plecoptera. Clutch size consisted of two eggs, a synapomorphy of gymnophthalmids. Vanzosaura multiscutata exhibited continuous reproduction with sequential clutches and smaller eggs, whereas V. savanicola and V. rubricauda had seasonal reproduction with larger eggs. Morphological analyses revealed sexual dimorphism in V. multiscutata with males being larger, consistent with ecological and reproductive adaptations related to environmental conditions. Vanzosaura savanicola was the largest species. Diet is evolutionarily conserved while ecological factors shape morphology and reproductive strategies. Our results corroborate theoretical predictions from Boyce's hypothesis, highlighting predictable environmental conditions that act as critical selective pressures shaping larger body sizes and associated ecological advantages. The differences in body size and reproductive strategies between Cerrado and Caatinga underscore the evolutionary significance of climatic predictability and resource stability.
Southern Appalachian Mountains are a global plethodontid salamander diversity hotspot. These salamanders are lungless ectotherms requiring cool and moist abiotic conditions to forage and reproduce. Northwestern North Carolina (NWNC) harbors similar plethodontid communities as those found further south but comprising different regional species. This region lacks recent demographic data for Plethodon communities. We estimated abundance and detection probabilities of three plethodontid salamanders from the southern crystalline ridges and mountains of NWNC using binomial mixture models. We found that across four sites, the abundance of Plethodon yonahlossee, Plethodon cylindraceus, and Plethodon wehrlei ranged from 1196-1978 individuals/ hectare (ind/ha),1170-1830 ind/ha, and 1422-2719 ind/ha respectively. We also found that relative humidity and days since last precipitation event were important covariates in predicting detection probability. This study serves as an updated understanding of relative abundance within NWNC terrestrial salamander communities using modern hierarchical modeling techniques because few studies have focused on Plethodon salamander communities in this region. By understanding the relative abundance of species within these terrestrial communities, we can better understand how communities and populations will respond to climate and anthropogenic changes. Additionally, by identifying abiotic factors that influence detection probability we can further focus sampling under favorable conditions (e.g., humid and rainy nights) and predict how detection may shift because of climate change.
.-Hydroperiod, or the length of time that a water body remains inundated, is an important factor for developmental progression of aquatic-breeding amphibians. In addition, predation risk has direct and nonconsumptive effects (NCEs) on amphibians and is intrinsically tied to hydroperiod. Some amphibians exhibit plasticity during development to mitigate environmental stressors, such as accelerated development in response to short hydroperiods and antipredator traits and behaviors. Amphibians often experience hydroperiod and NCEs concurrently, but few experimental studies have investigated effects of multiple stressors on salamander larvae. We conducted a mesocosm experiment with three hydroperiod treatments (short, medium, and constant) and two NCE treatments (presence or absence of aqueous predator cues from Lepomis macrochirus). We measured life history traits at metamorphosis to determine degree of developmental plasticity exhibited by Ambystoma texanum (Small-mouthed Salamander). Larval period, mass, and body size increased with longer hydroperiods but were not significantly affected by NCEs or interaction of hydroperiod and NCEs, suggesting a lack of synergistic or additive effects between these stressors. Compared to the control, salamanders in the short hydroperiod group metamorphosed 14.5% earlier, and were both 49% lighter in mass and 14.8% smaller in size on average. Smaller size at metamorphosis is associated with fitness costs in other Ambystoma, suggesting that developmental plasticity in response to short hydroperiods could eventually have population-level impacts for A. texanum. Understanding effects of environmental stressors on A. texanum is important for predicting their adaptability to climate change-induced shifts in water availability and introduced predators.
.-Road ecology examines the detrimental impacts of roads on biodiversity with an emphasis on threats to wildlife posed by collisions and habitat fragmentation. This study aimed to identify hotspots and hot moments of reptile and amphibian roadkill along two extensive Brazilian highways: BR-040 and RJ-122. Additionally, we presented a detailed list of roadkill reptiles and amphibians and proposed mitigation measures for wildlife mortality. We conducted this study within the Atlantic Forest in Southeastern Brazil, along a 180.4-km stretch through nine municipalities (BR-040) and a 34-km section in Rio de Janeiro State (RJ-122). We collected the following data from each carcass: location, date, and taxonomic identification to the lowest level possible. We used the DeadCanMove R package to identify statistically significant roadkill hotspots based on a Poisson spatial process, and we summarized the results with boxplots and geographical maps. We analyzed the relationship between identified hotspots and forest fragments along highways via logistic regression. We recorded 933 reptiles (44 species) and 481 amphibians (15 species) along BR-040 and RJ-122. Snakes (67.84% on BR-040, 57.89% on RJ-122) were the most common victims. The roadkill rate was 0.04 per km/month for BR-040 and 0.08km/month for RJ-122. Hotspot analysis revealed locations influenced by high speed limits and dense land cover, underscoring an urgency for conservation efforts and mitigation strategies, particularly in hotspots. We also observed a paradoxical pattern of species resilience in degraded areas near rainforest remnants, where proximity to protected areas and road characteristics appeared to contribute to mortality. We recommend periodic reassessments of hotspots and propose wildlife passages with directional fences as effective multi-species mitigation strategies. Our study provides valuable insights into roadkill dynamics, aiding in creating safer roads and effective conservation efforts.
Behavioral traits such as risk-taking and agonistic behavior have been investigated in several turtle species because they are important for fitness and often correlate with one another. We measured risk-taking and active defense (attacks) of wild-caught Snapping Turtles (Chelydra serpentina) in an outdoor experimental setting to test predictions about how these traits relate. We quantified response to a threat (an approaching novel object) and measured movement latency, exploration, and activity in the arena. We did not find any correlations between risk-taking measurements, nor did risk-taking correlate with defensive response. There were no differences between sexes or sizes, which could be due to a limited behavioral repertoire on land. However, we found that time since handling was negatively correlated with the agonistic response, highlighting the importance of considering the effect of time since capture on behavioral assays. Overall, our study on risk-taking and agonistic behavior in wild Snapping Turtles revealed no correlation between these traits on land but emphasized the impact of time since capture on threat response behaviors.
.-Sexual selection in amphibians is often based on size and color dimorphism, and most studies have used anurans. Sexual selection in urodeles remains understudied. Dorsal coloration of Fire Salamanders (Salamandra salamandra) has traditionally been interpreted as an aposematic signal. However, recent findings suggest that dorsal pigmentation may also exhibit sexual dimorphism and be important in mate choice. Here, we investigated a large population of Salamandra salamandra terrestris to explore relationships among sex, dorsal spot number, and yellow surface area. We found significant sexual dimorphism: females displayed a higher number of dorsal spots whereas males exhibited greater overall yellow surface area coverage. Moreover, spot number was negatively correlated with yellow surface area in both sexes, indicating a trade-off between spot fragmentation and continuous yellow patches. These results expand upon previous research by contributing a much larger data set and jointly analyzing spot number and yellow surface area. They suggest that pigmentation in Fire Salamanders could function not only as a protective signal against predators but also as a sexually selected trait. The possible role of dorsal coloration in mate choice warrants further investigation.
.-Spot-tailed Earless Lizards (STEL; Holbrookia lacerata, Plateau, and H. subcaudalis, Tamaulipan) are cryptic, elusive lizards, of which Tamaulipan STEL have been identified as candidates for potential federal threatened status listing. Environmental DNA (eDNA) has been proposed as a method with the potential to quickly assess areas for presence of STEL because eDNA is a non-destructive method that does not require animal capture. Therefore, we assessed the potential of using eDNA as a viable survey technique to assess the presence of STEL. Although development of eDNA could not distinguish Holbrookia at the species level, the designed assay detected the target genus from soil samples in 67% of cases when STEL were known to be present. We found that STEL needed to be in contact with soil substrate for at least 24 h to reliably detect their eDNA. Exposure of soil samples to ultraviolet light and/or high humidity increased the likelihood of obtaining a poor-quality sample that failed endogenous sample integrity checks. Consequently, there was a 77-80% chance of obtaining a false-negative result for STEL eDNA. In addition, locating specific sites where STEL had rested in soil for adequate time was akin to "finding a needle in a haystack." Lures or pheromones to entice STEL to specific locations away from direct ultaviolet light for eDNA sampling may improve eDNA detection, but such lures have not been identified. Additional research aimed at improving methodology and better understanding of biological and environmental variables in detecting eDNA of terrestrial reptiles is needed. Until then, eDNA is not recommended as a survey technique to assess the presence of STEL.
Sexual dimorphism refers to phenotypic differences between males and females of a species. In amphibians, sexual dimorphism in body size (sexual size dimorphism, SSD) and proportions is a result of complex selective forces which improve reproduction and survival. Dimorphic characters can covary with body size, showing different patterns of allometry. Although cloacal shape is an important character to differentiate sexes in salamanders, this trait has not been evaluated in paedomorphic Ambystoma species. We analyzed sexual dimorphism in several body characters and allometric patterns in paedomorphic Ambystoma ordinarium, previously assigned to sex only by cloacal shape. To confirm the sex assigned to individuals in the field, we analyzed the vitellogenin concentration in plasma. Our results showed that females had wider tails, wider heads, longer gills and greater weights than males. Males possessed greater total length and longer tails. Allometric patterns of both sexes showed a positive relationship between body size and mass. Vitellogenin concentration was significantly higher in individuals without cloacal bulging, suggesting that vitellogenin quantification and cloacal size are useful for differentiating males from females in A. ordinarium. The female-biased sexual dimorphism in body size and allometry probably resulted from a complex suite of selective forces such as fecundity and sexual selection acting differently upon the sexes.
.-Temporal variations in reproductive activity of cooccurring and closely related frog species can facilitate their coexistence. We investigated whether reproductive activity temporally varies among three coexisting Pristimantis species by analyzing monthly variation in body size, presence of reproductive individuals and juveniles, and gonadal development. We found female-biased sexual dimorphism in body size across all three species. Males reached sexual maturity at smaller sizes than females. A male-skewed sex ratio was evident in Pristimantis merostictus and Pristimantis Bacchus, whereas a higher number of females was observed in Pristimantis miyatai. Males of all three species exhibited continuous reproductive activity. Whereas P. merostictus females reproduced year-round, reproduction in P. miyatai and P. Bacchus was concentrated in the first half of the year, ceasing during the period of highest rainfall before the driest season. Therefore, we identified two patterns of reproductive activity: continuous in P. merostictus, with juvenile recruitment occurring every month, and prolonged in P. miyatai and P. Bacchus with reproductive peaks during the dry seasons and juvenile recruitment from April to December and from July to October, respectively. Although reproductive activity of the three species coincided temporally, differences in reproductive patterns and timing of juvenile recruitment suggest subtle reproductive variation among these species that share the same habitat.
.-The Rhinella granulosa group currently comprises 13 species distributed from Panama to South America. Descriptions of anuran calls have provided significant taxonomic information in studies involving problematic species groups. Herein, we revisit acoustic features of the advertisement calls in three of these species: Rhinella major, Rhinella bergi and Rhinella dorbignyi. In addition, we analyzed release calls of R. bergi and R. azarai. We discuss geographical variation in calls, comment on their frequency band structure, and compare calls with those described previously. To search for discrimination among populations of R. major, we used the random forest model, multidimensional scaling analysis, and Wilcoxon-Mann-Whitney rank sum tests. Advertisement calls consisted of a long-lasting trill of a variable pulse number (2-8) distinctive to each species, with the presence of one harmonic in R. bergi. Release calls consisted of multiple notes, pulsed or not, with the presence of harmonics. This marks the first time that harmonics have been reported for that species. Additionally, we found that temporal characteristics (e.g., note duration) varied among populations of R. major, whereas dominant frequency remained a stereotyped property.
Length-weight relationships are useful tools for estimating biomass and understanding ecological roles of aquatic species. In this study, we present parameters of these relationships for nine tadpole species, one tadpole family, and a general model for pond tadpoles. Tadpoles in the Atlantic Forest in Brazil were collected using active search, and their length (L in cm) and dry weight (W in g) were measured to estimate the parameters alpha and beta using the equation log10(W)= log10(alpha) + beta log10(L). The parameter beta ranged from 1.38 to 3.41 across species, with r2 values ranging from 0.45 to 0.97, reflecting the substantial morphological variation among tadpole families and species. The coefficients for the general model for pond tadpoles were beta = 2.33 and alpha = 0.019 (r2= 0.71), providing a reliable estimate when species-specific data are unavailable. This is the first study to report length-weight relationships for tropical tadpoles, providing valuable data for estimating tadpole biomass in Atlantic Forest aquatic ecosystems. These relationships enable researchers to rapidly assess tadpole biomass from length measurements alone, facilitating research on their ecological roles and the potential impacts of their decline on aquatic ecosystem functioning in one of the world's most threatened biodiversity hotspots.
Estimating individual survival is critical for understanding wildlife population dynamics and engaging effectively in conservation efforts. Individual survival rates can be difficult to estimate for secretive animals such as snakes, making demographic studies of snakes rare. Ages are difficult to estimate for snakes, but survival estimates that are based on body size eliminate the need for age data. However, modeling a time-varying individual covariate such as body size is difficult when individuals are rarely recaptured. We conducted a capture-mark-recapture study of Alameda Whipsnakes (Masticophis lateralis euryxanthus), a species listed as threatened at both the state and federal levels in California. To determine how whipsnake survival varies with body size, we used a growth model in a Bayesian framework to fill in missing individual covariate values when animals were not encountered and then used these values in a hierarchical capture-mark-recapture model estimating survival based on body size. We observed a strong relationship between body size and survival. Apparent survival increased dramatically from the smallest sizes to a snout-vent-length of approximately 450 mm before leveling out as intermediate-tomaximum body sizes were reached. We estimated annual apparent survival for adults as 53% for females and 59% for males. Our study provides the first survival estimates for M. lateralis euryxanthus, which represent foundational demographic variables for understanding population dynamics in this threatened species.
.-Variations in environment can lead to differences in life-history traits across anuran species. Increased environmental stress can result in increased age at sexual maturity, slower growth, longer longevity, and larger body size, among others. Sexual size dimorphism (SSD) refers to how multiple selective forces drive evolution of sex-specific body size. Our aims were to study sexual size dimorphism (SSD) in Pleurodema nebulosum, and to understand demographic life-history traits such as age structure, age at maturity, and longevity. Chronological formation of lines of arrested growth was analyzed in relation to reproductive activity and SSD. We observed sexual dimorphism in body size, with females reaching a significantly larger size than males. According to our skeletochronology results, P. nebulosum females reach sexual maturity at a later age than males. Therefore, females grow more slowly and delay sexual maturity, giving them more time to allocate energy to growth. On the other hand, males were on average younger than females. This pattern may be due to higher predation rates during the reproductive period, due to vulnerability from calling behavior.
The Upland Burrowing Treefrog, Smilisca dentata, classified as endangered by the International Union for the Conservation of Nature, are primarily threatened by land-use change. This study presents the results of the first systematic, quantitative analysis of one of its populations, conducted in 2005 within a 1.3 km2 area in southern Aguascalientes, Mexico. We analyzed the influence of environmental and habitat conditions on the population. We estimated a population size of 595.1 1 197.8 individuals; over 50% were adults, and the sex ratio biased toward females. About 25% of females had ovarian oocytes, although no reproductive activity was observed. Surface activity occurred from July to September, gradually declining over that period, with most individuals found far from disturbed areas. No spatial segregation among age or sex categories was detected. Activity was restricted to moderate temperatures, no more than 26 degrees C, and high humidity. Males were active over a wider temperature range, whereas nongravid females were active over a broader humidity range; gravid females showed the narrowest humidity range preference. The presence of rain, high wind, and lack of cloud cover limited activity. The main diet items were in the orders Coleoptera and Hymenoptera. Habitat characterization revealed signs of disturbance, particularly changes to the dominant plant species and composition of superficial soil. This study provides new ecological context for future fieldwork, monitoring, and updated conservation risk assessments related to management of this endangered species. We recommend studies on the climate resilience of individuals to assess their vulnerability to global warming. In addition, we emphasize the need to conserve as much intact and connected habitat as possible in the region. RESuMEN.-La rana arboricola de madriguera de tierras altas, Smilisca dentata, clasificada como amenazada por la Union Internacional para la Conservacion de la Naturaleza, esta principalmente amenazada por el cambio de uso de suelo. Este estudio presenta los resultados del primer analisis sistematico y cuantitativo de una de sus poblaciones, realizado en 2005 en un area de 1.3 km2 en el sur de Aguascalientes, Mexico. Analizamos la influencia de las condiciones ambientales y del habitat sobre la poblacion. Estimamos un tama & ntilde;o poblacional de 595.1 +/- 197.8 individuos, con mas del 50% adultos y una razon sexual sesgada hacia hembras; alrededor del 25% de las hembras presentaron ovocitos ovaricos, aunque no se observo actividad reproductiva. La actividad superficial ocurrio de julio a septiembre, disminuyendo gradualmente, y la mayoria de los individuos se encontraron lejos de areas perturbadas. No se detecto segregacion espacial entre categorias de edad o sexo. La actividad se restringio a temperaturas moderadas, no mayores a 26 degrees C, y alta humedad. Los machos estuvieron activos en un rango mas amplio de temperaturas, mientras que las hembras no gravidas usaron un rango mas amplio de humedad; las hembras gravidas mostraron la preferencia mas estrecha en cuanto a humedad. La presencia de lluvia, vientos fuertes y la falta de nubosidad limitaron la actividad. Los principales elementos en la dieta fueron de los ordenes Coleoptera e Himenoptera. La caracterizacion del habitat revelo signos de disturbio, particularmente cambios en la dominancia de especies de plantas y en la composicion superficial del suelo. Este estudio aporta un nuevo contexto ecologico para futuros trabajos de campo, monitoreo y actualizaciones en las evaluaciones de riesgo para la conservacion. Recomendamos estudios sobre resiliencia climatica de los individuos para evaluar su vulnerabilidad al calentamiento global. Ademas, enfatizamos en la necesidad de conservar la mayor cantidad posible de habitat intacto y conectado en la region.
.-Mamushis (Gloydius blomhoffii) are widespread and common venomous snakes in Japan. Generally, G. blomhoffii are considered a nocturnal species, but some literature suggests that these snakes may be active also during daytime. We conducted radiotelemetric surveys in a mountainous forest in Kyoto to clarify the seasonal and diurnal activities of G. blomhoffii. We defined snake body exposure (visible or hiding) as an index of snake activity. We recorded a total of 295 fixes (187 during daytime and 108 at night) for nine snakes from 2020 to 2021. Time of day did not affect snake body exposure. Environment, season, and air temperature influenced body exposure tendency. Monitored snakes were usually visible when in forest habitats, whereas they were frequently hiding under shelters in riverside habitats. Mean home range size of G. blomhoffii was 1.03 ha and was relatively small compared to other snake species. Mean daily displacement was higher in August and September and lower in other months. We conclude that G. blomhoffii are a cathemeral species, active both during daytime and at night, and vary their activity and movement depending on season, temperature, and environment. The different tendencies of body exposure between forest and riverside habitats likely reflect a strategy to avoid predators and/or overheating. Unlike previous visual-based anecdotal information, use of radiotelemetry enabled us to reveal the true activity patterns of G. blomhoffii without biases related to searching ability.
