Crystian Sadiel Venegas-Barrera

ECOLOGY OF THE MEXICAN ALPINE BLOTCHED GARTER SNAKE (THAMNOPHIS SCALARIS)

Abstract We report the first information on seasonal abundance, sex ratio, body size, reproduction, and diet for a population of Thamnophis scalaris from the State of Mexico. Data were collected during 1992 and from 1998 to 2000 at Toluca. Thamnophis scalaris showed a bimodal peak of activity in spring-early summer and in autumn. The sex ratio of adults was significantly different from 1:1, but can be misleading because of the unknown natural history of T. scalaris. Sexual size dimorphism was only apparent in relative tail length of adults. Four litters were born from July 1 to 17. Mean litter size was 7.0 ± 1.4 snakes per litter. Male and female neonates were of similar snout-vent length (SVL) and mass at birth. The sex ratio of neonates was 1:1. Of the stomachs examined, 81% contained earthworms and 19% contained vertebrates. Vertebrates (lizards and viperine snakes) were ingested only by T. scalaris >40.0 cm SVL. This suggests an ontogenetic shift in the diet of T. scalaris. The mean vertebrate prey mass was 21.4 ± 10.0% of snake mass. No differences were found in prey type between the sexes.

Temporal stability of an endemic Mexican treefrog

The demographic characteristics of an amphibian population fluctuate independently over time, mainly in response to the temporal variation of environmental factors, especially precipitation and temperature. These temporal fluctuations may contribute to the size of an amphibian population and could be used to determine the current conservation status of a species. During a five year (2004–2008) period, we studied the relative abundance, sex ratio, and age-sex structure of a population of metamorphosed individuals of the endemic treefrog Hyla eximia in Central Mexico. We also studied the species’ relationship with climatic variables such as temperature and precipitation. We found an interannual constant abundance during the study period. However, interannual differences were observed in the population structure by age-sex category (males, females, or juveniles), with decreased abundance of males and juveniles during the rainy months (August–November). The annual abundance of H. eximia was positively correlated with rainfall, but negatively with monthly temperature. We found the sex ratio was male-biased (2:1), except for year 2008. Also, differences in snout-vent length (SVL) were found between years, suggesting changes in recruitment of new individuals. We conclude that variations in abundance, and frequencies by age-sex category, of H. eximia are related to seasonal variations in temperature and precipitation characteristics of temperate zones. However, this temporal stability may suggest that anurans have an unusual capacity to persist even in the face of human-induced habitat change.

Influence of Habitat Heterogeneity on Structure and Composition of a Chrysomelidae (Coleoptera) Assemblage in a Temperate Forest in Northeast Mexico

Abstract. Disturbance in natural areas occurs as a result of various processes on various spatio-temporal scales, generating a heterogeneous mosaic of environmental characteristics. The effect of such change on diversity patterns has been explained by the hypothesis of habitat heterogeneity. Modifications in abiotic and biotic factors such as plant density influence the composition and structure of assemblages of phytophagous insects. Response of the leaf beetle (Coleoptera: Chrysomelidae) assemblage to such changes was evaluated in an oak (Quercus spp.) forest in the Altas Cumbres Natural Protected Area, Victoria, Tamaulipas, Mexico. The delimited mosaic was classified into four categories according to the length of time since the last disturbance: 1 year, 10 years, 30 years, and 40 years. Disturbance time categories were delimited using remote sensing techniques from LANDSAT satellite scenes. Leaf beetles were sampled each month from February to April 2016 in 10 plots per category. The numbers of herbaceous and shrubby plants in each plot were counted with the aim of estimating the plant density of each category and relating values with differences among communities of Chrysomelidae. In total, 1,056 individuals of six subfamilies and 37 species were obtained, with Centralaphthona sp. 1 the most abundant. Thirteen species were specialists, while Helocassis crucipennis (Boheman, 1855) occurred in the most niches. Leaf beetles preferred high plant densities and were most abundant and had most species richness in the category of 10 years since the last disturbance. The community had aggregate spatial distribution that might reflect significant biological patterns. Alpha diversity indices indicated the 10-year category was most even, with Hypolampsis sp. 1 the dominant species. In contrast, least evenness was in the 1-year category where Centralaphthona sp. 1 was dominant; the species might indicate permanent disturbance. The community had low species turnover among the categories of disturbance and is therefore expected to have high gamma diversity. Inventory of the study area had 82.4% completeness; however, categories of 10 and 30 years required more sampling effort. Results supported the hypothesis of habitat heterogeneity, because observed community patterns did not occur by chance. This suggested that environmental heterogeneity because of disturbance positively influenced composition and community structure of Chrysomelidae, and observed patterns responded to intra- and interspecific interactions.

Community Structure of Ichneumonidae (Hymenoptera) in a Mangrove Area in the Coastal Zone of Tamaulipas, Mexico.

espanolSe describe la estructura de las comunidades de Ichneumonidae en un area de manglar y 2 localidades cercanas con diferentes tipos de vegetacion. El area de estudio esta ubicada en los limites de las regiones Neartica y Neotropical en sur del estado de Tamaulipas, Mexico. Las muestras se recolectaron con una trampa Malaise en cada sitio durante 1 ano. La riqueza potencial de especies se determino con el modelo de Clench, los indices de diversidad de Simpson y Shannon-Wiener, asi como las posibles diferencias entre las comunidades con el analisis multivariado de Permanova. Los grados relativos de influencia de las variables espaciales, de tiempo y de distribucion biogeografica en las estructuras comunitarias se determinaron mediante analisis de correspondencia multiple. Los datos mostraron que el area de manglar tiene la mayor riqueza potencial de especies y que hubo diferencias significativas entre las 3 comunidades de ichneumonidos. Las estructuras comunitarias dependen de la distribucion biogeografica de las especies y del mes de recolecta, mientras que las estructuras poco dependientes, del tipo de vegetacion. Tres especies obtenidas en este estudio representan nuevos registros para Mexico y 5 para el estado de Tamaulipas. EnglishThe structure of Ichneumonidae communities in a mangrove area and 2 nearby locations with different vegetation types are described. The study area is located within the limits of the Nearctic and Neotropical regions in the southern part of the state of Tamaulipas, Mexico. Samples were collected with a Malaise trap at each site over a one-year period. We estimated the potential species richness with the Clench model, the Simpson and Shannon-Wiener diversity indexes and the possible differences among communities at different sites using Permanova multivariate analysis. The relative degrees of influence of space, time, and biogeographical distribution on the community structures of ichneumonid wasps were determined using multiple correspondence analyses. Our results showed that the mangrove area had the highest potential species richness, and that there were significant differences among the 3 ichneumonid communities. The community structures depend primarily on the biogeographical distribution of species and secondarily on the month of collection, whereas the type of vegetation contributed with lower variation. Three species obtained in this study are new records for Mexico, and 5 for Tamaulipas.

Intraspecific variation in the diet of the Mexican garter snake Thamnophis eques

The Mexican Garter Snake (Thamnophis eques) is a terrestrial-aquatic generalist that feeds on both aquatic and terrestrial prey. We describe size-related variation and sexual variation in the diet of T. eques through analysis of 262 samples of identifiable stomach contents in snakes from 23 locations on the Mexican Plateau. The snake T. eques we studied consumed mostly fish, followed in lesser amounts by leeches, earthworms, frogs, and tadpoles. Correspondence analysis suggested that the frequency of consumption of various prey items differed between the categories of age but not between sex of snakes, and the general pattern was a reduction of prey item diversity with size of snake. Snake length was correlated positively with mass of ingested prey. Large snakes consumed large prey and continued to consume smaller prey. In general, no differences were found between the prey taxa of male and female snakes, although males ate two times more tadpoles than females. Males and females did not differ in the mass of leeches, earthworms, fishes, frogs and tadpoles that they ate, and males and females that ate each prey taxon were similar in length. We discuss proximate and functional determinants of diet and suggest that the observed intraspecific variation in T. eques could be explored by temporal variation in prey availability, proportions of snake size classes and possible sexual dimorphism in head traits and prey dimensions to assess the role of intersexual resource competition.

Diversidad y zoogeografía de los moluscos terrestres de la sierra de Tamaulipas, México

Diversity and biogeography of Mexican terrestrial gastropods is poorly known. The terrestrial mollusks of the Sierra of Tamaulipas were surveyed from October 1988 to November 2005. A total of 482 samples were obtained from 30 localities, characterized with different vegetation types. Thirty-one genera and 46 species belonging to 18 families are recorded. The primary zoogeographical relationships are characterized by the presence of neotropical and neartic affinities (17 species: 37%) and the endemic taxa (11 species: 24%). The family Spiraxidae has the largest number of endemic species (6). The biogeographical value in this area is 3.78.

Visual Detection of Speckles in the Fish Xenotoca variata by the Predatory Snake Thamnophis melanogaster in Water of Different Turbidity.

Semi-aquatic snakes integrate visual and chemical stimuli, and prey detection and capture success are therefore linked to the display of visual predatory behavior. The snake Thamnophis melanogaster responds preferentially to individuals of the fish Xenotoca variata with a greater number of bright, colorful spots (lateral speckles) compared with those with a smaller number; however, water turbidity can reduce underwater visibility and effect the vulnerability of fish. In this study, we tested whether the presence of iridescent speckles on the flanks of male X. variata interacted with water turbidity to modify the predatory behavior displayed by the snake T. melanogaster. We predicted that in an experimental laboratory test, the snakes would increase the frequency of their predatory behavior to the extent that the water turbidity decreases. The snakes were tested at six different levels of water turbidity, in combination with three categories of male fish (with few, a median number of, or many speckles). The results showed that in a pool with high or zero turbidity, the number of speckles is not a determining factor in the deployment of the predatory behavior of the snake T. melanogaster toward X. variata. Our findings suggest that snakes can view the fish at intermediate percentages of turbidity, but the number of speckles in male X. variata is irrelevant as an interspecific visual signal in environments with insufficient luminosity. The successful capture of aquatic prey is influenced by integration between chemical and visual signals, according to environmental factors that may influence the recognition of individual traits.