Hertz et al. (1993) designed what is now the most widely used protocol to analyse the thermal strategies and efficiency of small squamates. Preferred temperature range (Tp) is one of the most important variables required for determining the thermal efficiency index, and is calculated by monitoring the body temperature of the individuals in an enclosure containing a thermal gradient. Although thermoregulation studies of lizards have traditionally employed thermal gradients under laboratory conditions, this approach is not suitable for snakes given that such thermal gradients do not accurately represent their natural thermal environment and thus may result in snakes selecting suboptimal temperatures. Here, we compare the results of this thermal efficiency protocol using a laboratory thermal gradient (LG) and a semi-captivity thermal gradient (SCG) in the rattlesnake Crotalus polystictus. We found traces of seasonal variation in the SCG Tp, but this could not be assessed in the LG. Tp from the LG was much higher (29 – 34.3 °C) than from the SCG (22.5-30.9 °C). Values for the accuracy of thermoregulation (db) and thermal quality of the environment (de) indices from the LG were consistently higher than from the SCG. However, the efficiency of thermoregulation (E) was higher when calculated from the SCG. Tp estimates were wider than most that have been obtained from other snake species, suggesting that C. polystictus is eurythermic. The Blowin Demers and Weatherhead index was nearly identical in both gradients. Results from the LG indicated that C. polystictus is an inaccurate and inefficient thermoregulator, due to the higher temperatures chosen in this environment. In contrast, results from the SCG suggested that it is a highly accurate and active thermoregulator. We suggest that the LG could represent a stressful environment for snakes, and, as a consequence, they might select higher temperatures to increase anti-predatory performance at the expense of less efficient thermoregulation. Generally, a thermal gradient that more accurately replicates the natural habitat of snake species should reduce stress and result in more robust estimates of thermoregulatory variables.

Anuran vocalizations transmit relevant information that aids in individual recognition and sexual selection by females. When studied over time, vocalizations can help us to understand reproductive phenology. Here, we used an automated recording system to obtain calls of 4 anurans in southeastern Mexico, described the calling phenology of the species and tested its relationship with environmental variables. We performed Generalized Linear Mixed Effects Models (GLMM's) to explore possible relationships between calling and environmental variables. The hylid species (Agalychnis callidryas, A. moreletii and Dendropsophus ebraccatus) showed a clear calling pattern; they began calling in April/May and increased in their intensity during the rainy season, from June to September. Craugastor loki showed, contrarily, no clear patterns of calling, preferring to call almost continuously throughout the year. Among the environmental factors tested, only minimum temperature and the amount of days without rain had an effect (positive and negative, respectively) on calling activity of the hylids, but we found that calling from other species had greater positive effects within the group. There was a strong phenological overlap in the calling behavior of these species, which may suggest that competition for site of calling or acoustic niche partitioning can be present in the community.

Las especies que forman parte de una comunidad pueden estar restringidas por los recursos disponibles. Uno de ellos es el espacio acústico, donde en caso de existir solapamiento puede verse afectada la comunicación entre conespecíficos y, potencialmente, la reproducción. Por esta razón, cabe esperar que las comunidades de anuros que presentan una marcada estacionalidad tengan una segregación de nicho en el espacio acústico, debido a su solapamiento en el tiempo. Mediante sistemas de grabación automática (SGA) y grabaciones manuales (370 horas de grabación), registramos la actividad acústica y las vocalizaciones de una comunidad de anuros en Nahá, Chiapas, México durante el periodo octubre 2013 a junio 2014. A partir de 216 cortes de audio pertenecientes a 7 especies, analizamos las grabaciones y registramos 15 características acústicas para cada especie a fin de evaluar el solapamiento espacial, temporal y estructural del nicho acústico, además de estimar la amplitud del nicho mediante el cálculo del hipervolumen. Encontramos que el solapamiento espacial fue muy bajo, mientras que el temporal fue muy alto y se puede observar una marcada fenología (junio, agosto y septiembre en promedio > 0.58). El solapamiento estructural de nicho acústico también fue alto y significativo de acuerdo al índice de Czekanowski. Sin embargo, a pesar de que los hipervolúmenes fueron similares, la segregación del uso de la frecuencia dominante fue muy notoria. A pesar de que no observamos partición de nicho acústico en la comunidad, es muy probable que exista una compensación evolutiva entre el solapamiento acústico relacionada con las redes de comunicación que, aunque significa competencia, representa al mismo tiempo protección contra depredadores.