The Herpetological Journal

DOI: https://doi.org/10.33256/32.4.176182

pp.176-182

Authors: Daniel Kane & Christopher J. Michaels

Abstract: Captivity can provide a resource-rich environment for snakes which may lead to over-conditioning of individuals. We compared captive and wild populations of Bitis arietans to see if a difference in scaled mass index (SMI) existed between the samples. Male B. arietans had significantly higher SMI in captivity than in the wild; there was no difference between wild and captive females. A sex-related difference in SMI between wild male and female B. arietans, evident in the wild, was not found in captivity. These results suggest that the captive management of B.arietans may require review to prevent over-conditioning of male snakes, and that this may be informed by further comparative research on wild and captive populations of this species.

Keywords: Body condition, captivity, scaled mass index, Viperinae

Authors: Daniel Kane & Christopher J. Michaels

DOI: https://doi.org/10.33256/32.4.183189

pp. 183-189

Authors: Mikaella M.G. Lock & Richard A. Griffiths

Abstract: The ability to detect snakes in the field may be influenced by phenotypic and morphological variables attributable to the target species. These variables include body size, colouration, and body posture. To test what effect these variables had on detectability by surveyors, plasticine model grass snakes were distributed along a predetermined transect in reptile habitat. Detections of different types of snake models along the transect were compared between two groups of inexperienced students and those of a single experienced observer. The experienced surveyor detected 72 % of all the snake models, compared to 53 % and 58 % by the inexperienced groups. All groups detected more larger snakes than smaller snakes, and more uncoiled snakes than coiled snakes. The presence of a yellow/black collar did not influence the detection of the snakes. The results demonstrate the observer bias that may be inherent in surveys of snakes due to variation in size and posture of the target animals. Accounting for such biases in the design of reptile surveys and providing appropriate training and experience for volunteers may improve the validity and interpretation of data collected within citizen science programmes.

Keywords: population assessment, imperfect detection, citizen science, survey protocol

Authors: Mikaella M.G. Lock & Richard A. Griffiths

DOI: https://doi.org/10.33256/32.4.190197

pp. 190-197

Authors: Patricia Marques do A. Oliveira, Carlos A. Navas and Pedro M. Sales Nunes

Abstract: Lizard diets can be influenced by several factors, such as age, physiological aspects, food availability, behaviour and foraging mode. The latter can be an important predictor of the type of prey consumed. This study analysed Ameivula ocellifera and Tropidurus cocorobensis diets, both of which are psammophiles and coexist in an area of Caatinga in north-eastern Brazil, but use different foraging modes. Lizard stomachs were examined, and prey categories were quantified by frequency of occurrence, number, volume and relative importance index. We used PERMANOVA and SIMPER analyses to understand the dissimilarities among diets. Additionally, we estimated the degree of trophic niche overlap between species using the Pianka index. The most frequently consumed food item by A. ocellifera was Isoptera and Formicidae (Hymenoptera) for T. cocorobensis. The trophic niche overlap between the species was approximately 0.24 and, although there were many consumed prey categories in common, the proportion at which these prey categories were consumed was quite divergent. For example, the consumption of plant material, which was present in the diet of both species, was much more important for T. cocorobensis compared to the active forager A. ocellifera. Our results indicate that despite sharing the same space and consuming the same prey types, these species have significant differences in their diets. Furthermore, these divergences can be explained by several factors in the environment and even by the evolutionary history of each species, which are included in different families and are not evolutionarily close to each other. 

Keywords: diet, niche overlap, foraging mode, plant consumption, competition