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Results for “Herpetological Journal”

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At least 37 records · Page 2Linked to original sources
USGS2018

Time-to-detection occupancy modeling: An efficient method for analyzing the occurrence of amphibians and reptiles

Occupancy models provide a reliable method of estimating species distributions while accounting for imperfect detectability. The cost of accounting for false absences is that detection and nondetection surveys typically require repeated visits to a site or multiple-observer techniques. More efficient methods of collecting data to estimate detection probabilities would allow additional sites to be surveyed for the same amount of effort, which would support more precise estimation of covariate effects to improve inference about underlying ecological processes. Time-to-detection surveys allow the estimation of detection probability based on a single site visit by one observer, and therefore might be an efficient technique for herpetological occupancy studies. We evaluated the use of time-to-detection surveys to estimate the occupancy of pond-breeding amphibians at Point Reyes National Seashore, California, USA, including variables that affected detection rates and the probability of occurrence. We found that detection times were short enough, and occupancy was high enough, to estimate reliably the probability of occurrence of three pond-breeding amphibians at Point Reyes National Seashore, and that survey and site conditions had species-specific effects on detection rates. In particular, pond characteristics affected detection times of all commonly detected species. Probability of occurrence of Sierran Treefrogs ( Hyliola sierra ) and Rough-Skinned Newts ( Taricha granulosa ) was negatively related to the detection of fish and pond area. Time-to-detection surveys can provide an efficient method for estimating detection probabilities and accounting for false absences in occupancy studies of reptiles and amphibians.

California↗
USGS2001

Morphometrics, sexual dimorphism, and growth in the Angonoka tortoise ( Geochelone yniphora ) of western Madagascar

The most recent description of the morphology of the rare endemic Madagascar tortoise, Geochelone yniphora was based on fewer than 20 specimens. We collected morphological data for 200 free‐ranging tortoises from five populations over a four‐year period. Tortoises ranged in size from 43.5 mm carapace length at hatching to a maximum of 481 mm in an adult male. We were able to develop a logistic regression model to predict the sex of adult tortoises in one of the five populations using principal component analysis; the model correctly predicted the sex of 25 of 26 adult tortoises. Growth of 40 tortoises was monitored and as in other chelonians, the annual relative growth rate decreased with age. The relative growth rate in adults was approximately 5% per year as compared to approximately 16% in juveniles. Juvenile tortoises accrued one scute growth layer per year.

African Journal of Herpetology↗
USGS2005

Population structure of the African Clawed Frog (Xenopus laevis) in maize-growing areas with atrazine application versus non-maize-growing areas in South Africa

The herbicide atrazine has been suggested to cause gonadal deformities in frogs and could possibly impact on reproduction. Since the early 1960s, atrazine has been used in large amounts in maize production areas of South Africa. These areas overlap with populations of the African Clawed Frog (Xenopus laevis) that has a wide distribution in southern Africa and is found in most water-bodies including those where atrazine residues are detected. The aim of this study was to compare various attributes of individual- and population-level responses of X. laevis from maize-growing and non-maize-growing areas. Xenopus laevis were studied in three reference and five maize-growing sites. Sex ratio, snout-vent length, body-mass and age profiles were found to be similar for populations in maize-growing and non-maize-growing areas. Our mark-recapture data indicated that all sites had robust populations. There were no significant relationships between exposure to atrazine and any of the parameters investigated in populations of X. laevis.

African Journal of Herpetology↗
USGS2005

Assessment of laryngeal muscle and testicular cell types in Xenopus laevis (Anura Pipidae) inhabiting maize and non-maize growing areas of South Africa

We tested the hypothesis that adult African clawed frogs (Xenopus laevis) inhabiting water bodies in maize-growing areas (MGA) of South Africa would exhibit differences in testicular structure compared to frogs from water bodies in non-maize-growing areas (NMGA) in the same locale. Adults of both sexes were collected during the autumn of 2002 in South Africa, and stereological analytical techniques were used to quantify the distribution of testicular cell types. In addition, total laryngeal mass was used as a gauge of secondary sex differences in animals from MGA and NMGA study sites. Evaluation of the total laryngeal mass revealed that there were no statistically significant differences between X. laevis of the same sex from the NMGA and MGA sites. Mean percent fractional-volume values for seminiferous tubule distribution of testicular cell types of mature X. laevis, ranged from 3-4% for spermatogonia, 26-28% for spermatocytes, 54-57% for spermatozoa, and 14-15% for other cells types. The mean percent volume for blood vessels ranged from 0.3-0.4%. These values did not differ significantly between frogs from NMGA and MGA areas. Collectively, these data demonstrated no differences in gonadal and laryngeal development in X. laevis collected in South Africa from MGA and NMGA areas and that there is little evidence for an effect of agricultural chemicals used in maize production functioning as endocrine disrupters in this species. Screening of X. laevis testes revealed a small incidence of Stage 1 testicular oocytes in adult male frogs collected from the NMGA (3%) and MGA (2%).

African Journal of Herpetology↗
USGS2002

Population dynamics of Eleutherodactylus coqui in cordillera forest reserves of Puerto Rico

Various aspects of population structure and dynamics of Eleutherodactylus coqui in two forest reserves (Maricao and Guilarte) of the central mountain range of Puerto Rico were determined between July 1997 and June 1998. Adult density ranged from 8–25 animals/100 m 2 for the wet season and 3–19 animals/100 m 2 for the dry season. Abundance of froglets and juveniles was also greater in the wet season compared to the dry season. By contrast, egg mass counts were greater in the dry season compared to the wet season. Adult body size increased from wet to dry season as population density declined and was found to differ significantly between forests. Adult E. coqui trapped at similar elevations were larger in Guilarte compared to those in Maricao. Average body size for Maricao and Guilarte populations were smaller than those reported for populations in eastern Puerto Rico. Comparing average snout–vent length among frogs from the Luquillo Mountains, Guilarte Forest, and Maricao Forest, a gradient of decreasing body size was observed from east to west across the island.

Puerto Rico↗
USGS2002

A new species of Echinosaura (Gymnophthalmidae) from Ecuador and Colombia with comments on other members of the genus and Teuchocercus keyi

A new species of the genus Echinosaura is described from the Pacific drainages of northern Ecuador and adjacent Colombia. Evaluation of variation among congeners justifies their recognition as distinct species instead of subspecies as previously proposed. The new lizard occurs in close proximity to Echinosaura horrida and Teuchocercus keyi .

Journal of Herpetology↗
USGS2002

Evaluation of canoe surveys for anurans along the Rio Grande in Big Bend National Park, Texas

Surveys for amphibians along large rivers pose monitoring and sampling problems. We used canoes at night to spotlight and listen for anurans along four stretches of the Rio Grande in Big Bend National Park, Texas, in 1998 and 1999. We explored temporal and spatial variation in amphibian counts and species richness and assessed relationships between amphibian counts and environmental variables, as well as amphibian-habitat associations along the banks of the Rio Grande. We documented seven anuran species, but Rio Grande leopard frogs ( Rana berlandieri ) accounted for 96% of the visual counts. Chorus surveys along the river detected similar or fewer numbers of species, but orders of magnitude fewer individuals compared to visual surveys. The number of species varied on average by 37% across monthly and nightly surveys. We found similar average coefficients of variation in counts of Rio Grande leopard frogs on monthly and nightly bases (CVs = 42–44%), suggesting that canoe surveys are a fairly precise technique for counts of this species. Numbers of Rio Grande leopard frogs observed were influenced by river gage levels and air and water temperatures, suggesting that surveys should be conducted under certain environmental conditions to maximize counts and maintain consistency. We found significant differences in species richness and bullfrog ( Rana catesbeiana ) counts among the four river stretches. Four rare anuran species were found along certain stretches but not others, which could represent either sampling error or unmeasured environmental or habitat differences among the river stretches. We found a greater association of Rio Grande leopard frogs with mud banks compared to rock or cliff (canyon) areas and with seepwillow and open areas compared to giant reed and other vegetation types. Canoe surveys appear to be a useful survey technique for anurans along the Rio Grande and may work for other large river systems as well.

Texas↗
USGS2002

An evaluation of population index and estimation techniques for tadpoles in desert pools

Using visual (VI) and dip net indices (DI) and double-observer (DOE), removal (RE), and neutral red dye capture-recapture (CRE) estimates, we counted, estimated, and censused Couch's spadefoot ( Scaphiopus couchii ) and canyon treefrog ( Hyla arenicolor ) tadpole populations in Big Bend National Park, Texas. Initial dye experiments helped us determine appropriate dye concentrations and exposure times to use in mesocosm and field trials. The mesocosm study revealed higher tadpole detection rates, more accurate population estimates, and lower coefficients of variation among pools compared to those from the field study. In both mesocosm and field studies, CRE was the best method for estimating tadpole populations, followed by DOE and RE. In the field, RE, DI, and VI often underestimated populations in pools with higher tadpole numbers. DI improved with increased sampling. Larger pools supported larger tadpole populations, and tadpole detection rates in general decreased with increasing pool volume and surface area. Hence, pool size influenced bias in tadpole sampling. Across all techniques, tadpole detection rates differed among pools, indicating that sampling bias was inherent and techniques did not consistently sample the same proportion of tadpoles in each pool. Estimating bias (i.e., calculating detection rates) therefore was essential in assessing tadpole abundance. Unlike VI and DOE, DI, RE, and CRE could be used in turbid waters in which tadpoles are not visible. The tadpole population estimates we used accommodated differences in detection probabilities in simple desert pool environments but may not work in more complex habitats.

Journal of Herpetology↗
USGS2002

Diet of Crotalus lepidus klauberi (Banded Rock Rattlesnake)

We describe the diet of Crotalus lepidus klauberi (Banded Rock Rattlesnake) using samples collected in the field and from museum specimens, as well as several records from unpublished reports. Most records (approximately 91%) were from the northern Sierra Madrean Archipelago. Diet consisted of 55.4% lizards, 28.3% scolopendromorph centipedes, 13.8% mammals, 1.9% birds, and 0.6% snakes. Sceloporus spp. comprised 92.4% of lizards. Extrapolation suggests that Sceloporus jarrovii represents 82.3% of lizard records. Diet was independent of geographic distribution (mountain range), sex, source of sample (stomach vs. intestine/feces), and age class. However, predator snout–vent length differed significantly among prey types; snakes that ate birds were longest, followed in turn by those that ate mammals, lizards, and centipedes. Collection date also differed significantly among prey classes; the mean date for centipede records was later than the mean date for squamate, bird, or mammal records. We found no difference in the elevation of collection sites among prey classes.

Journal of Herpetology↗
USGS2002

Natural history of a northern population of twin-spotted rattlesnakes, Crotalus pricei

The twin-spotted rattlesnake ( Crotalus pricei ) is a small-bodied pitviper that has received little attention in the literature to date. The species reaches the northern limit of its range in southeastern Arizona, where it inhabits higher elevations than any of the state's 10 other rattlesnake species. During 1997–2000, we captured, measured, and marked 127 C. pricei in Arizona's Chiricahua Mountains between 2530 and 2900 m elevation. We also used radiotelemetry to track the movements of 16 C. pricei in the study area during 1997–1998. Mean (± SE) snout–vent length of C. pricei was 387.8 ± 8.3 mm (range = 168–572), and mean mass was 53.5 ± 3.3 g (range = 3.6–188.5). Based on fecal analyses, lizards constituted the bulk of prey (74%), but the diet of C. pricei also included mammals, birds, and a conspecific. Mating was concentrated in August and early September and parturition took place during late July and August. Mean number of embryos was 3.94 ± 0.34 (range = 1–6) and female reproduction appeared biennial or less frequent. Based on shed and growth rates, female C. pricei develop embryos at 4–5 years of age. Gravid females maintained warmer body temperatures relative to substrate temperature than nongravid females or males, presumably by spending more time basking than other snakes. Radiotelemetry revealed that movement patterns varied from year to year, as males moved over six times farther per week during the 1998 monsoon season (July to September) than during the 1997 monsoon season. Additionally, use of talus slopes by males decreased during 1998. During dry years, such as 1998, males may be forced off talus into cooler microclimates where resources are less concentrated than on talus.

Journal of Herpetology↗
USGS2002

Tadpoles balance foraging and predator avoidance: Effects of predation, pond drying, and hunger

Organisms are predicted to make trade-offs when foraging and predator avoidance behaviors present conflicting demands. Balancing conflicting demands is important to larval amphibians because adult fitness can be strongly influenced by size at metamorphosis and duration of the larval period. Larvae in temporary ponds must maximize growth within a short time period to achieve metamorphosis before ponds dry, while simultaneously avoiding predators. To determine whether tadpoles trade off between conflicting demands, I examined tadpole ( Pseudacris triseriata ) activity and microhabitat use in the presence of red-spotted newts ( Notopthalmus viridescens ) under varying conditions of pond drying and hunger. Tadpoles significantly decreased activity and increased refuge use when predators were present. The proportion of active time tadpoles spent feeding was significantly greater in predator treatments, suggesting tadpoles adaptively balance the conflicting demands of foraging and predator avoidance without making apparent trade-offs. Tadpoles responded to simulated drying conditions by accelerating development. Pond drying did not modify microhabitat use or activity in the presence of predators, suggesting tadpoles perceived predation and hunger as greater immediate threats than desiccation, and did not take more risks.

Journal of Herpetology↗
USGS2003

Habitat segregation of Ambystoma gracile and Ambystoma macrodactylum in mountain ponds, Mount Rainer National Park, Washington, USA

Ambystoma gracile (Baird) and Ambystoma macrodactylum Baird are common salamander species occupying key trophic positions in mountain ponds and lakes of Mount Rainier National Park (MORA). Based on amphibian surveys conducted in ponds and lakes in the northeast quadrant of MORA during the summers of 1993a??1995, 20 sites were resampled in 1996 to document and evaluate distributions of the two species relative to site habitat characteristics. Distributions of larvae were assessed either by nearshore snorkel or visual encounter surveys of each study site. Twelve environmental variables representing pond and lake physical characteristics, water quality, and nutrient concentrations were measured. The occurrences at each site of three major habitat components (i.e., pond bottom firmness, coarse woody debris, and emergent/aquatic vegetation) were qualitatively estimated. Allotopic distributions of larval populations of both species were related to site elevation, maximum depth, organic content of bottom substrates, and surface area. Ambystoma gracile sites were larger, deeper, lower in elevation, had flocculent sediment higher in organic content, abundant coarse woody debris, and limited emergent/aquatic vegetation relative to A. macrodactylum sites. Ambystoma macrodactylum sites were smaller, shallower, higher in elevation, had firm sediments low in organic content, and had a greater occurrence of emergent/aquatic vegetation than did A. gracile sites. Two sites supported syntopic populations and exhibited many of the habitat characteristics observed at sites inhabited by each species. The distribution of each species in MORA was related to the interconnection between habitat characteristics of ponds and lakes and species life-history patterns and possibly interspecific interactions.

Washington↗
USGS2003

Desert tortoise ( Gopherus agassizii ) survival at two eastern Mojave Desert sites: Death by short-term drought?

Survival of adult Desert Tortoises ( Gopherus agassizii ) appears related to site-specific variation in precipitation and productivity of annual plants. We studied adult tortoise survival rates at two closely situated, but physiographically different, sites in the eastern Mojave Desert over a nine-year period (spring 1992 to spring 2001). Survival rates were initially derived from population surveys conducted over a three-year period and by radio-telemetry monitoring over a seven-year period beginning in 1994. After a period of initial stability, survival rates on the two sites diverged over the study period, and seven-year survival rates estimated from radio-telemetry monitoring were 0.900 and 0.269, respectively. A die-off in 1996 on the latter site appears to have been triggered by a period of drought, which began in the summer of 1995, coupled with a failure of annual vegetation production in 1996. Depressed survival rates on this site were associated with drought conditions during three of four years. Although the decline had the appearance of an epizootic, there were no clinical signs of disease. Relatively short-term drought, combined with little or no annual biomass, appears to have caused severe reductions in tortoise survival. If periods of drought-induced low survival are common over relatively small areas, then source-sink population dynamics may be an important factor determining tortoise population densities.

Journal of Herpetology↗
USGS2003

Chytridiomycosis in wild frogs from southern Costa Rica

In 1993, the amphibian fauna of Las Tablas, Costa Rica , began to decline, and by 1998 approximately 50% of the species formerly present could no longer be found. Three years later, at the Reserva Forestal Fortuna, in western Panama, a site approximately 75 km east southeast of Las Tablas, KRL encountered a mass die-off of amphibians and a subsequent decline in abundance and species richness. The epidemiological features of the anuran population declines and die-offs at both sites were similar, suggesting a similar cause. Herein we document the presence of the fungus, Batrachochytrium dendrobatidis, in dead and dying wild frogs collected at Las Tablas just prior to population declines of several anuran species.

Journal of Herpetology↗
USGS2003

Predicted sex ratio of juvenile Hawksbill Seaturtles inhabiting Buck Island Reef national monument, U.S. Virgin Islands

Hawksbill Seaturtles have temperature-dependent sex determination. As such, the resulting sex ratios are of conservational and ecological significance. Buck Island Reef is an interesting location for sex ratio studies since it represents a natural and unexploited foraging ground for hawksbills in the Caribbean. To examine sex ratios, blood samples were obtained from juvenile Hawksbill Seaturtles captured on Buck Island Reef over a four-year period. We used a radioimmunoassay to determine testosterone levels in those samples and compared those values to testosterone levels of juvenile hawksbills from the Caribbean whose sex has been verified by laparoscopy. The results of this study reveal a significantly female-biased sex ratio (approximately 80% female) occurs in this juvenile aggregation inhabiting Buck Island Reef .

U.S. Virgin Islands↗
USGS2005

Male Texas Horned Lizards increase daily movements and area covered in spring: A mate searching strategy?

Texas Horned Lizards, Phrynosoma cornutum , were tracked using fluorescent powder to determine exact daily movements. Daily linear movements and daily space use were compared between adult males and females. Lizards that traveled the greatest linear distances also covered the largest areas. In Oklahoma, adults emerge from hibernation in late April and early May and mate soon afterward. Males traveled significantly greater distances (and covered significantly larger areas in a day) than females in May but not after May. We propose that males move more and cover more area than females early in the mating season to intercept receptive females.

Oklahoma↗
USGS2005

Modeling anuran detection and site occupancy on North American Amphibian Monitoring Program (NAAMP) routes in Maryland

One of the most fundamental problems in monitoring animal populations is that of imperfect detection. Although imperfect detection can be modeled, studies examining patterns in occurrence often ignore detection and thus fail to properly partition variation in detection from that of occurrence. In this study, we used anuran calling survey data collected on North American Amphibian Monitoring Program routes in eastern Maryland to investigate factors that influence detection probability and site occupancy for 10 anuran species. In 2002, 17 calling survey routes in eastern Maryland were surveyed to collect environmental and species data nine or more times. To analyze these data, we developed models incorporating detection probability and site occupancy. The results suggest that, for more than half of the 10 species, detection probabilities vary most with season (i.e., day-of-year), air temperature, time, and moon illumination, whereas site occupancy may vary by the amount of palustrine forested wetland habitat. Our results suggest anuran calling surveys should document air temperature, time of night, moon illumination, observer skill, and habitat change over time, as these factors can be important to model-adjusted estimates of site occupancy. Our study represents the first formal modeling effort aimed at developing an analytic assessment framework for NAAMP calling survey data.

Maryland↗