Snake Species Richness Research Articles

Snakebite epidemiology, outcomes and multi-cluster risk modelling in Eswatini.

Halving snakebite morbidity and mortality by 2030 requires countries to develop both prevention and treatment strategies. The paucity of data on the global incidence and severity of snakebite envenoming causes challenges in prioritizing and mobilising resources for snakebite prevention and treatment. In line with the World Health Organisation's 2019 Snakebite Strategy, this study sought to investigate Eswatini's snakebite epidemiology and outcomes, and identify the socio-geographical factors associated with snakebite risk. Programmatic data from the Ministry of Health, Government of Eswatini 2019-2021, was used to assess the epidemiology and outcomes of snakebite in Eswatini. We developed a snake species richness map from the occurrence data of all venomous snakes of medical importance in Eswatini that was subjected to niche modelling. We formulated four risk indices using snake species richness, various geospatial datasets and reported snakebites. A multivariate cluster modelling approach using these indices was developed to estimate risk of snakebite and the outcomes of snakebite in Eswatini. An average of 466 snakebites was recorded annually in Eswatini. Bites were recorded across the entire country and peaked in the evening during summer months. Two cluster risk maps indicated areas of the country with a high probability of snakebite and a high probability of poor snakebite outcomes. The areas with the highest rate of snakebite risk were primarily in the rural and agricultural regions of the country. These models can be used to inform better snakebite prevention and treatment measures to enable Eswatini to meet the global goal of reducing snakebite morbidity and mortality by 50% by 2030. The supply chain challenges of antivenom affecting southern Africa and the high rates of snakebite identified in our study highlight the need for improved snakebite prevention and treatment tools that can be employed by health care workers stationed at rural, community clinics.

Uneven species occurrence and richness of lowland snakes (Serpentes, Squamata) in Terengganu, Peninsular Malaysia, with new locality records.

This study documents information on the composition, diversity, richness, and temporal occurrence of snakes at Sekayu's lowland forest (SLF), Terengganu, Peninsular Malaysia for the first time. The snakes recorded within the SLF were sampled opportunistically from 2013 to 2019, employing the Visual Encounter Survey method (VES) and L-shape pitfall traps with drift fences. Forty-six snake species from 37 genera belonging to the nine families were recorded, of which 11 were new records to Terengganu. Individual-based rarefaction and extrapolation curves were not reaching asymptote, indicating that additional species can be recorded at the study area. Non-parametric species richness estimators estimated and produced a range between 51 and 57 species. ACE was the best estimator based on the quantitative evaluation. All species showed some variations of occurrence patterns across months. Fourteen species were only encountered once across the sampling years, and interestingly 11 of them were only detected during the rainy season (late October to January). In general, the number of species richness, abundance, and rare species were high during this season. Species richness of snakes is high at SLF but sampling effort should be intensified, especially during these rainy months, to obtain a robust estimated snake species richness in SLF. Terengganu harbor considerably high species richness of snakes with a total of 71 species to date (excluding marine snakes), but snake diversity is still underestimated as only a few localities were surveyed in the past years, primarily at the northern part. Future surveys should be commenced at the central and southern parts of Terengganu to complement the current investigation.

Latitudinal and environmental patterns of species richness in lizards and snakes across continental North America

AbstractAimLittle is known about the contributions of individual clades to the broader latitudinal diversity gradients of lizards and snakes in North America. Additionally, the environmental variables underpinning these patterns have not been extensively studied, nor have the relationships between squamate species richness and biome variety, a proxy for habitat heterogeneity. Here, we deconstruct the latitudinal diversity gradient of squamates and investigate lizard and snake species richness in relation to environmental gradients and biomes across continental North America.LocationNorth America, excluding islands.TaxonSquamata (lizards and snakes).MethodsWe collated a suite of environmental variables (n = 10) and squamate species ranges (n = 1,152) in an equal‐area grid system (100 × 100 km cells) spanning continental North America. We deconstructed the latitudinal diversity gradient of squamates and examined species richness patterns for all lizards, all snakes and several individual squamate clades. We used multiple linear regressions to determine which environmental factors are most important for each squamate clade. Finally, we documented species richness within biomes and tested for correlations between species richness and biome variety.ResultsSquamates exhibit a strong latitudinal diversity gradient across continental North America. Snakes are more widespread and have a stronger gradient than lizards. Our multiple linear regression results indicate strong associations between species richness and environmental variables for all individual squamate clades analysed; temperature variables are strongly positively correlated with species richness. Biome variety is more strongly correlated with lizard species richness than snake species richness. Squamates are most species‐rich in tropical/subtropical forests, deserts and mangroves.Main conclusionsMost snake clades in North America exhibit strong latitudinal diversity gradients, but only two lizard clades, Dactyloidae (anoles) and Gekkota (geckos), display strong gradients and thus drive the overall lizard pattern. Squamate clades differ in their responses to environmental gradients, as reflected by their species richness patterns, with warmer climates generally harboring more species. Lizards are more strongly associated with habitat heterogeneity than snakes are, consistent with results from previous studies. Squamates in more rapidly shifting biomes (e.g. deserts, mangroves) may face a greater risk of extinction from impending climate change.

Reptiles of the Serra das Torres Natural Monument: using the Rapid Assessment method to fill a knowledge gap in the Atlantic Forest of southeastern Brazil

Abstract: Data on the composition of local reptile assemblages in several Brazilian ecosystems can still be considered relatively restricted in scope in most cases. In this study, we conducted surveys in the Serra das Torres Natural Monument, located in the municipalities of Atílio Vivacqua, Muqui, and Mimoso do Sul, using the Rapid Assessments method (RAP) during 30 days in the rainy season of 2018. We sampled actively for approximately 1320 hours with a 6-10 person crew, supplemented by 720 hours of passive sampling (30 bucket-days) using pitfall traps with drift fences. We recorded 34 reptile species during our sampling method (2 amphisbaenid, 11 lizards, and 21 snakes) and an occasional encounter, after the end of sampling, that added a chelonian species to the list, Hydromedusa maximiliani, totaling 35 reptile species. The Dipsadidae was the family with the greatest snake species richness and, the Gymnophtalmidae had the greatest lizard species richness. The species richness recorded in the Serra das Torres Natural Monument (Ntotal = 35) represents ca. 27% of all reptile species found in the state of Espírito Santo (N = 130). The most abundant lizard species was Leposoma scincoides followed by Ecpleopus gaudichaudii and, the most abundant snake species was Bothrops jararaca being markedly higher than that recorded in similar studies. Twenty-seven percent of the reptile species recorded in our study are endemic to the Atlantic Forest and 30% (N = 10) have been recorded less than five times previously in the Brazilian state of Espírito Santo. Our study reinforces the need for the conservation of the Serra das Torres Natural Monument because of its importance as a reservoir of a considerable portion of the reptile biodiversity of Espírito Santo state, and of the Atlantic Forest biome as a whole.

Searching for rare and secretive snakes: are camera-trap and box-trap methods interchangeable?

Abstract ContextAdvancements in camera-trap technology have provided wildlife researchers with a new technique to better understand their study species. This improved method may be especially useful for many conservation-reliant snake species that can be difficult to detect because of rarity and life histories with secretive behaviours. AimsHere, we report the results of a 6-month camera-trapping study using time lapse-triggered camera traps to detect snakes, in particular the federally listed Louisiana pinesnake (Pituophis ruthveni) in eastern Texas upland forests in the USA. MethodsSo as to evaluate the efficacy of this method of snake detection, we compared camera-trap data with traditional box-trapping data collected over the same time period across a similar habitat type, and with the same goal of detecting P. ruthveni. Key resultsNo differences in focal snake species richness were detected across the trap methods, although the snake-detection rate was nearly three times higher with camera traps than with the box traps. Detection rates of individual snake species varied with the trapping method for all but two species, but temporal trends in detection rates were similar across the trap methods for all but two species. Neither trap method detected P. ruthveni in the present study, but the species has been detected with both trap methods at other sites. ConclusionsThe higher snake-detection rate of the camera-trap method suggests that pairing this method with traditional box traps could increase the detection of P. ruthveni where it occurs. For future monitoring and research on P. ruthveni, and other similarly rare and secretive species of conservation concern, we believe these methods could be used interchangeably by saturating potentially occupied habitats with camera traps initially and then replacing cameras with box traps when the target species is detected. ImplicationsThere are financial and logistical limits to monitoring and researching rare and secretive species with box traps, and those limits are far less restrictive with camera traps. The ability to use camera-trap technologies interchangeably with box-trap methods to collect similar data more efficiently and effectively will have a significant impact on snake conservation.

Snake species richness predicts breeding distribution of short-toed snake eagle in central Italy

Birds of prey, as top predators, play a key role in ecosystem functioning by regulating prey populations and, by means of cascade effects, promoting biodiversity. This makes them adequate sentinels of ecosystem health. Here we analyse the relationship between the occurrence of breeding short-toed snake eagle (Circaetus gallicus) and both the richness of potential prey species and landscape characteristics by taking into account two different spatial scales (i.e. nest-site scale and landscape scale). The short-toed snake eagle offers an interesting case study for investigating the relationships between top predators, prey diversity, and habitats, because it is an extremely specialised raptor that feeds on mesopredators, mostly snakes. Additionally, short-toed snake eagles are mainly threatened by changes in agriculture and land use in Europe, which have reduced the extent of suitable hunting habitats, and by the decrease in snake populations. Our study was conducted in the Latium Region (central Italy) in 2007, where most of the Italian breeding population is concentrated. By means of habitat selection analyses using generalised linear models, our results showed that the species selected breeding areas characterised by low elevations, rugged slopes, and high snake species richness at the nest-site scale (1 km2). At the landscape scale (25 km2), the best model showed that birds selected areas characterised by lower elevations for nesting, with a tendency towards intermediate values of wood cover and high snake species richness. Our study highlights the strong relationship between snake species richness and the occurrence of breeding eagles at both spatial scales, with optimal breeding sites located closer to hunting areas than expected by chance. This study provides further support for the role of short-toed snake eagles as sentinel species for Mediterranean habitats, and highlights the link between the location of nesting sites and the occurrence of human-modified landscapes characterised by high prey richness.

Geographic patterns and ecological factors correlates of snake species richness in China

Understanding large-scale geographic patterns of species richness as well its underlying mechanisms are among the most significant objectives of macroecology and biogeography. The ecological hypothesis is one of the most accepted explanations of this mechanism. Here, we studied the geographic patterns of snakes and investigated the relationships between species richness and ecological factors in China at a spatial resolution of 100 km×100 km. We obtained the eigenvector-based spatial filters by Principal Coordinates Neighbor Matrices, and then analyzed ecological factors by multiple regression analysis. The results indicated several things: (1) species richness of snakes showed multi-peak patterns along both the latitudinal and longitudinal gradient. The areas of highest richness of snake are tropics and subtropical areas of Oriental realm in China while the areas of lowest richness are Qinghai-Tibet Plateau, the grasslands and deserts in northern China, Yangtze-Huai Plain, Two-lake Plain, and the Poyang-lake Plain; (2) results of multiple regression analysis explained a total of 56.5% variance in snake richness. Among ecological factors used to explore the species richness patterns, we found the best factors were the normalized difference vegetation index, precipitation in the coldest quarter and temperature annual range ; (3) our results indicated that the model based on the significant variables that (P<0.05) uses a combination of precipitation of coldest quarter, normalized difference vegetation index and temperature annual range is the most parsimonious model for explaining the mechanism of snake richness in China. This finding demonstrates that different ecological factors work together to affect the geographic distribution of snakes in China. Studying the mechanisms that underlie these geographic patterns are complex, so we must carefully consider the choice of impact-factors and the influence of human activities.

Salinity influences the distribution of marine snakes: implications for evolutionary transitions to marine life

Secondary transitions from terrestrial to marine life provide remarkable examples of evolutionary change. Although the maintenance of osmotic balance poses a major challenge to secondarily marine vertebrates, its potential role during evolutionary transitions has not been assessed. In the current study, we investigate the role of oceanic salinity as a proximate physiological challenge for snakes during the phylogenetic transition from the land to the sea. Large‐scale biogeographical analyses using the four extant lineages of marine snakes suggest that salinity constrains their current distribution, especially in groups thought to resemble early transitional forms between the land and the sea. Analyses at the species‐level suggest that a more efficient salt‐secreting gland allows a species to exploit more saline, and hence larger, oceanic areas. Salinity also emerged as the strongest predictor of sea snake richness. Snake species richness was negatively correlated with mean annual salinity, but positively correlated with monthly variation in salinity. We infer that all four independent transitions from terrestrial to marine life in snakes may have occurred in the Indonesian Basin, where salinity is low and seasonally variable. More generally, osmoregulatory challenges may have influenced the evolutionary history and ecological traits of other secondarily marine vertebrates (turtles, birds and mammals) and may affect the impact of climate change on marine vertebrates.

Estimating the snake species richness of the Santubong Peninsula (Borneo): a computer-simulation

The snake species richness of the Santubong Peninsula, Sarawak, Borneo, has been estimated previously by fitting a Weibull model to the rarefied species accumulation curve. In the present study, the estimation procedure was simulated in order to shed more light on its validity, i.e. its accuracy and precision. First, the estimate was updated on the basis of an additional, small-scale, survey carried out in 2011. Subsequently, survey-data were used to construct a simulation database. Twenty samples were randomly drawn from this database. Each sample was transformed into a rarefied species accumulation curve to which a Weibull model was fitted. For comparison, various related models were fitted as well. All applied models resulted in a downwardly biased estimate. The Weibull model performed best, providing the estimate of species richness with the smallest bias and thus highest accuracy. As for the precision of the estimate, a rather wide confidence interval was established.

Estimating the snake species richness of the Santubong Peninsula (Borneo) in two different ways

The distribution of Borneo’s species across the island is far from well-known. This is particularly true for snakes which are hard to find. Given the current rate of habitat destruction and consequent need for conservation strategies, more information is required as to the species composition and richness of specific areas of potential conservation priority. An example is the Santubong Peninsula, Sarawak, Malaysia, part of which has recently been gazetted as a National Park. In this paper, the snake species richness of the Santubong Peninsula is estimated on the basis of data obtained during 450 survey-hours. Thirty-two species were recorded. Negative exponential and Weibull functions were fitted to the rarefaction curve. The Weibull function exhibited a high goodness-of-fit, as opposed to the negative exponential function. On the basis of the fitted Weibull function, the total number of snake species was estimated to be 42. A similar estimate of 40 was obtained by applying the nonparametric Chao I estimator. Thus, less than a third of Borneo’s known 139 land snakes inhabit the Santubong Peninsula. Extrapolation of the fitted Weibull function demonstrated that direct measuring of herpetofaunal species richness of species-rich tropical ecosystems is unfeasible given the required search time. I advocate that the use of estimates is unavoidable.

Secondary Rain Forests are not Havens for Reptile Species in Tropical Mexico

ABSTRACTA widely accepted biodiversity crisis in the tropics has been recently challenged by claims that secondary forests will gradually restore biodiversity losses. This prediction was examined for the herpetofauna in Quintana Roo, Mexico. Quantitative sampling (108 transects) of reptiles was undertaken monthly (January–September 2004) along a vegetation gradient covering induced grasslands, and regrowth and primary rain forests. A total of 35 species was found, 14 being present in and five showing dependence on mature forests. Lizards contributed &gt; 90 per cent of the individuals observed. Reptile abundance and snake species richness was highest in primary forests, even though the lower abundance and richness did not differ between regrowth forest and induced grasslands. Multivariate ordinations and ANOSIM tests displayed clear differences in assemblage structure among vegetation types, mainly caused by contrasting abundances of lizard species having distinctive arboreal or terrestrial habits. There was no evidence that snake assemblages differed between secondary forests and induced grasslands. Microhabitat availability had a key role in shaping species composition through the vegetation gradient. Our results dismiss the hypothesis that secondary forests can act as reservoirs of primary forest reptile diversity on the basis that many taxa depend largely on habitat quality and have specialized life‐history traits, and that biological succession does not guarantee the recovery of assemblage complexity.

Elevational gradients of diversity for lizards and snakes in the Hengduan Mountains, China

Comparing elevational gradients across a wide spectrum of climatic zones offers an ideal system for testing hypotheses explaining the altitudinal gradients of biodiversity. We document elevational patterns of lizard and snake species richness, and explore how land area and climatic factors may affect species distributions of lizards and snakes. Our synthesis found 42 lizard species and 94 snake species known from the Hengduan Mountains. The lizards are distributed between 500 and 3500 m, and the snakes are distributed between 500 and 4320 m. The relationship between species richness and elevation for lizards and snakes is unimodal. Land area explains a significant amount of the variation in lizard and snake species richness. The cluster analysis reveals pronounced distinct assemblages for lizards and snakes to better reflect the vertical profiles of climate in the mountains. Climatic variables are strongly associated with lizard and snake richness along the elevational gradient. The data strongly implicate water availability as a key constraint on lizard species richness, and annual potential evapotranspiration is the best predictor of snake species richness along the elevational gradient in the Hengduan Mountains.

ECOLOGICAL PATTERNS OF ANTHROPOGENIC MORTALITY OF SUBURBAN SNAKES IN AN AFRICAN TROPICAL REGION

The ecological patterns of anthropogenic mortality of snakes in the Niger Delta (southeastern Nigeria), as well as factors that attract or force snakes into human settlements, are investigated in this paper. The snake species richness in suburban environments of the Niger Delta is remarkable, and includes about 36% of the species presently known from the area as a whole. The proportion of dangerous species is low. Anthropogenic mortality rates stood at a conservative mean estimate of 0.110 snakes/effort hour, while the mortality frequency peak occurred in the rainy month of June (0.559 snakes/effort hour). This mortality peak coincided with the onset of the inundation period of the swamps. The flooding of their forest habitat, and the presence of abundant food supply and shelters seem to be the main factors favoring the establishment of snake populations in urban environments. About 50% of snakes were killed intentionally by people, but vehicles and trapping with snares (set for mammals) were also importa...