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Paramesotriton hongkongensis has a highly restricted distribution in southern China, and a comprehensive study of the species' basic ecology in aquatic and terrestrial habitats has not been previously undertaken. Using mark-recapture methods, we assessed seasonal patterns of breeding populations in four streams in Hong Kong every 3 wk over 18 mo (2007–2009). We examined diet and body condition of newts in the four focal and six additional streams. We surveyed transects radiating outward from breeding pools to determine the extent of terrestrial habitats used. In the four focal streams, we made 3436 captures of adult newts, comprising 1312 unique individuals. Breeding occurred primarily during the dry, cool season and extended over 8 mo. Individuals remained in breeding pools for an average of 45 days, suggesting that populations in pools were changing throughout the breeding season and that most individuals had a 10-mo terrestrial phase. Sex ratio changed across the breeding season, with males making up larger proportions of populations earlier in the season. Breeding site fidelity averaged 24% and was density-dependent. Among the 47 identified prey types identified in the diet of 406 newts, the most important prey were Brotia snails, Caridina shrimp, newt eggs, baetid mayflies, and calamoceratid caddisflies, in composite making up 63% of total prey volume and 82% of total prey abundance. Cannibalism of eggs and larvae, primarily by females, largely explained differences in diet between sexes. We documented no systematic difference in adult body condition (size-weight relationship) among streams. Fifteen individuals were found in forested habitats within 100 m of the nearest stream, except a single individual located 228 m away. Our work demonstrates that P. hongkongensis occurs at relatively high densities in stream pools during a protracted breeding season, in which individuals show site fidelity but probably do not breed every year. The species appears to be a generalist predator in most aquatic habitats. Although individuals spend most of the year on land, we still have little understanding of the spatial extent of terrestrial habitat use by the species. Future investigations should focus on the species' ecology in terrestrial habitats and on determining the amount of forest cover around breeding sites necessary to protect P. hongkongensis populations in Hong Kong.
Although adult crocodilians have few predators (mostly humans and other crocodilians), hatchlings and eggs are killed and consumed by a diverse array of invertebrates, fishes, anurans, reptiles, birds, and mammals. We review published literature to evaluate the incidence of predation in crocodilian populations, and the implications of that mortality for crocodilian life-history evolution. Presumably because predation is size-dependent, small-bodied crocodilian taxa appear to be more vulnerable to predation (across a range of life stages) than are larger-bodied species. Several features of crocodilian biology likely reflect adaptations to reducing vulnerability to predation. For example, the threat of predation may have influenced the evolution of traits such as nest-site selection, maternal care of eggs and hatchlings, crèche behavior in hatchlings, and cryptic coloration and patterning. Even for such large and superficially invulnerable taxa such as crocodilians, the avoidance of predation appears to have been a significant selective force on behavior, morphology, and ecology.
We review the taxonomic status of the snakes belonging to the genus Atractus from the Pantepui region on the basis of morphological characters (meristic, morphometric, color pattern, and hemipenis). We redescribe and illustrate the holotype of A. insipidus, correcting the elevation of the type locality and providing its exact coordinates. We report the third known specimen of A. riveroi on the basis of an individual collected in the Sierra Parima close to the Venezuela/Brazil border. We report the geographical variation of A. steyermarki, expanding its known distribution on the basis of specimens collected in Guyanese tepuis, and consider the species a senior synonym of A. guerreroi. We also report the geographical variation in meristic, morphometric, color pattern, and hemipenial characters of A. tamessari on the basis of the discovery of new specimens. Finally, we provide a key to the Atractus of the Guiana Shield and discuss on the evolution of some particular features of hemipenial morphology in the genus.
Se revisó el estado taxonómico de las serpientes pertenecientes al género Atractus del Pantepui, a través de caracteres morfológicos (merísticos, morfométricos, patrón de coloración y hemipene). Se redescribe e ilustra el holotipo de A. insipidus y se detalla la ubicación y altitud de la localidad tipo. Se registra el tercer ejemplar conocido de Atractus riveroi a través de un individuo proveniente de la Sierra de Parima, cerca a la frontera Venezuela/Brasil. Atractus steyermarki se considera un sinónimo senior de A. guerreroi. Se amplía la distribución y variación geográfica de esta especie, a través de ejemplares capturados en tepuis de Guyana. Se describe también la variación geográfica en los caractéres merísticos, morfometricos, patrón de coloración y hemipene de A. tamessari, basado en el hallazgo de nuevos individuos. Por último, se presenta una clave para los Atractus del Escudo de Guayana y se discute la evolución de algunas características particulares de la morfología del hemipene en el género.
Numerous factors have contributed to declines in populations of the federally threatened Agassiz's Desert Tortoise (Gopherus agassizii) and continue to limit recovery. In 2010, we surveyed a low-density population on a military test facility in the northwestern Mojave Desert of California, USA, to evaluate population status and identify potential factors contributing to distribution and low densities. Estimated densities of live tortoises ranged spatially from 1.2/km2 to 15.1/km2. Although only one death of a breeding-age tortoise was recorded for the 4-yr period prior to the survey, remains of 16 juvenile and immature tortoises were found, and most showed signs of predation by Common Ravens (Corvus corax) and mammals. Predation may have limited recruitment of young tortoises into the adult size classes. To evaluate the relative importance of different types of impacts to tortoises, we developed predictive models for spatially explicit densities of tortoise sign and live tortoises using topography (i.e., slope), predators (Common Raven, signs of mammalian predators), and anthropogenic impacts (distances from paved road and denuded areas, density of ordnance fragments) as covariates. Models suggest that densities of tortoise sign increased with slope and signs of mammalian predators and decreased with Common Ravens, while also varying based on interaction effects involving these predictors as well as distances from paved roads, denuded areas, and ordnance. Similarly, densities of live tortoises varied by interaction effects among distances to denuded areas and paved roads, density of ordnance fragments, and slope. Thus multiple factors predict the densities and distribution of this population.