Morphological variation in the common lancehead populations: sexual dimorphism and ontogenetic patterns

The common lanceheadBothrops jararacais widespread in the Atlantic Forest inBrazil. The species is known to show a marked sexual dimorphism pattern, with thefemale being larger than the male. However, most efforts in clarifying morphologicalvariation between the sexes are often focused on a single population. In this paper,we investigate how sexual dimorphism and ontogenetic trajectories vary among pop-ulations as well as the ontogenetic trajectories ofB. jararaca. We analyzed 211 spec-imens from a coastal and a highland population and measured 17 morphologicaltraits, including linear and meristic characteristics, and the analysis revealed a clearbut variable effect of sex and population. Females were larger than males in all eval-uated populations. Furthermore, females in the coastal population were generallysmaller than in the highland population but had significantly more scales. Widespreadspecies often experience differential environmental pressures even in terms of bioticand abiotic factors. We attribute the results found herein to specificities in prey avail-ability and climatic conditions which affect the ontogenetic pattern between the sexesand the populations, resulting in specific sexual dimorphism patterns.

Body shape and diet reflect arboreality degree of five congeneric snakes sympatric in the Atlantic forest

The substrate use by animals may influence both their morphology and diet. Species of the genus Chironius are among the most conspicuous frog-eating, arboreal snakes in South America. The aim of the present study was to investigate whether diet and morphology relate to substrate use in five sympatric Chironius species from the Atlantic Forest. Our hypothesis is that habitat pressure is strong enough so that even closely related species will present differences. We collected morphological and diet data from specimens of C. bicarinatus, C. exoletus, C. foveatus, C. fuscus, and C. laevicollis housed in scientific collections. Information on habitat use were obtained by monitoring free-ranging animals using thread-bobbins and also from the literature. Our results demonstrate that C. foveatus is the most arboreal species, and C. laevicollis is the most terrestrial among the five studied species. Chironius foveatus is the slenderest, with one of the longest relative tail lengths, the narrowest ventral scales, the highest vertebral density, the largest eye diameter, green body color, and diet based on tree frogs (Hylidae). These traits indicate a higher arboreality for this species. On the other extreme, C. laevicollis is the stoutest species, and has the shortest tail, the largest head, the lowest vertebral density, and diet based on ground-living frogs (Leptodactylidae). These traits indicate pronounced terrestriality for this species. The other three species have traits intermediate between the extremes showed by C. foveatus and C. laevicollis. We found evidence for a close relationship between arboreality or terrestriality, morphology, and diet.

Seasonal activity of Bothrops jararaca (Serpentes, Viperidae): optimizing foraging while avoiding predators

The peak of activity of Bothrops jararaca is in the rainy season. This pitviper feeds mainly on small mammals and is preyed upon by several avian and mammal predators. However, the association between jararaca's seasonal activity with that of their prey and predators remains unknown. The present study tested the hypothesis that the peak activity of B. jararaca coincides with that of their prey and predators, mainly due to favorable climatic conditions during this period. Snake activity was inferred from standardized searches and animals deposited in herpetological collections. Seasonal activity of prey was inferred from monthly sampling carried out over one year using pitfall and Sherman traps. Plasticine models were used to infer predation risk. Analyses of predator and prey abundance were performed, taking into account climatic variables, and models explaining this relationship were proposed. Activity of both B. jararaca and its prey was higher in the rainy season. Activity of the latter was positively correlated with temperature and rainfall. Predator activity, however, was higher in the dry season and negatively correlated with temperature and rainfall but positively correlated with humidity. The peak activity of B. jararaca in the rainy season might favor foraging activities, since this period coincides with greater prey abundance and decreased predation risk. During the dry season when resource availability is low, predators feed opportunistically, encountering dangerous prey such as B. jararaca. In summary, the activity pattern showed by the snake clearly increases its survival.

Effects of urbanization on Bothrops jararaca populations in São Paulo municipality, Southeastern Brazil

Quantitative and qualitative alterations in the environment may have serious ecological consequences for populations of native species. Isolated forest fragments, such as those surrounded by highly urbanized areas, may function similarly to oceanic islands with differences in species diversity compared to mainland areas. These differences may include changes in prey availability and predator pressure, with consequent effects on growth and size of species that interact with those prey and predators. Here, we investigate body size, prey availability, and predation pressure in populations of Bothrops jararaca in two forest fragments within an urban environment in southeastern Brazil (a completely isolated, small forest fragment and a large, well-connected forest fragment). While we found no differences in mean body size or stoutness between the two populations, we did find larger specimens in the small isolated fragment. Prey availability and predator pressure also were significantly lower in the small isolated fragment. The urban environment significantly changes the population ecology between the two locations. These results suggest that lower food availability in the isolated fragment did not decrease the growth rate of B. jararaca, but the low predator pressure increased longevity, resulting in a higher proportion of large snakes in this population.

Effects of urbanization on Bothrops jararaca populations in São Paulo municipality, Southeastern Brazil

Quantitative and qualitative alterations in the environment may have serious ecological consequences for populations of native species. Isolated forest fragments, such as those surrounded by highly urbanized areas, may function similarly to oceanic islands with differences in species diversity compared to mainland areas. These differences may include changes in prey availability and predator pressure, with consequent effects on growth and size of species that interact with those prey and predators. Here, we investigate body size, prey availability, and predation pressure in populations of Bothrops jararaca in two forest fragments within an urban environment in southeastern Brazil (a completely isolated, small forest fragment and a large, well-connected forest fragment). While we found no differences in mean body size or stoutness between the two populations, we did find larger specimens in the small isolated fragment. Prey availability and predator pressure also were significantly lower in the small isolated fragment. The urban environment significantly changes the population ecology between the two locations. These results suggest that lower food availability in the isolated fragment did not decrease the growth rate of B. jararaca, but the low predator pressure increased longevity, resulting in a higher proportion of large snakes in this population.