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Understanding of resource requirements of vulnerable species is key for conservation planning. Here, we used stable carbon (δ13 C) and nitrogen isotopes (δ15 N) of hair from giant armadillos (Priodontes maximus) to understand individual resource use. We collected hair from 19 giant armadillos analyzing 34 samples from the Brazilian Pantanal and compared the resource use between sexes and age classes. We also assessed the relationship of isotopic values with individuals' body mass and the habitat type used. We observed a wide variation in resource use by giant armadillos, showing that individuals consume prey that feeds on distinct resources and occupies different habitat types, indicating that there is individual variation in foraging behavior. Most giant armadillos presented a mixed diet (C3 /C4 resources, forests/open areas), but a quarter of individuals had strictly C4 diets (open areas). Males are more prone to forage on C4 resources, presenting an isotopic niche 2.6-times larger than that of females. Subadults presented diets more associated with habitats with high arboreal cover (C3 resources, forests), while adults foraged more in open areas (C4 resources). This result is mirrored by the positive relationship between δ13 C values and body mass, suggesting that larger giant armadillos tend to feed more in open areas. We observed that δ13 C values decreased as individuals increased the use of habitats with high arboreal cover. We stress the importance of conserving the natural mosaic in the Pantanal landscape for the species persistence, given that giant armadillos require all habitat types to fulfill their dietary, spatial, and developmental needs.

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RESUMO

Ontogenetic changes in herbivory are generally not consistent with ontogenetic changes in defensive traits of woody plants. This inconsistency suggests that other factors may affect ontogenetic trajectories in herbivory. We tested the hypothesis that top-down factors contribute to differences in foliar losses to insects between juvenile and mature trees in tropical and boreal forests. We used artificial caterpillars made of modelling clay to compare predation rates between saplings and mature trees of two common forest species, Siparuna guianensis in Brazil (tropical site) and Betula pubescens in Finland (boreal site). Leaf area losses to chewing insects in saplings were 2.5-fold higher than in mature trees in both species. Physical plant defences (measured as specific leaf area, SLA) did not differ between saplings and mature trees in the boreal forest, whereas in the tropical forest, SLA was greater in saplings than in mature trees. Attack rates on the model prey by birds were higher in the boreal forest, whereas attack rates by arthropod predators were higher in the tropical forest. Overall, predation rates on model prey were consistently higher on mature trees than on saplings at both sites, but in the boreal site, this pattern was primarily driven by birds, whereas in the tropical site, it was primarily driven by arthropod predators. We conclude that the effect of predation on herbivorous insects may considerably contribute to ontogenetic differences in herbivory, but the relative roles of different predatory groups and of top-down and bottom-up factors may vary between environments.

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RESUMO

Sexual dimorphism in snakes has been mainly evaluated for size and number of some morphological traits, but few studies address on sexual shape dimorphism. Here we evaluated the existence of sexual size and shape dimorphism in the semi-fossorial snake Atractus reticulatus. We use linear and geometric morphometrics to evaluate differences between sexes and among different ontogenetic stages (neonates, juveniles and adults). We have shown that A. reticulatus is sexually dimorphic for some traits such as body length and head shape, with females being larger and having more robust heads than males, but the sexes do not differ in head size. Males and females are sexually dimorphic in head shape even in neonates, suggesting that this differentiation is prenatal. Differences in head shape may be associated with trophic segregation, allowing females to feed on larger prey than males. Body size dimorphism progressively increases throughout the ontogenetic stages, which is possibly related to the late sexual maturation of females and/or different growth rates between the sexes. We also found that males and females shows some sex-specific patterns towards static and ontogenetic allometry, with males showing stronger predictive response on static allometry than females, whereas females have ontogenetic allometry, but males do not. Additionally, the allometric slopes in A. reticulatus between sexes converge by presenting similar shapes as head size increases, an expected result for sexes with similar lifestyles. Further investigation on some physiological and natural history aspects in Atractus will be particularly useful for a better understanding of the significance of the morphological differences found in this study.

RESUMO

Movement and exchange of individuals among habitats is critical for the dynamics and success of reef fish populations. Size segregation among habitats could be taken as evidence for habitat connectivity, and this would be a first step to formulate hypotheses about ontogenetic inter-habitat migrations. The primary goal of our research was to find evidence of inter-habitat differences in size distributions and density of reef fish species that can be classified a priori as habitat-shifters in an extensive (~600km²) Caribbean shelf area in NW Cuba. We sampled the fish assemblage of selected species using visual census (stationary and transect methods) in 20 stations (sites) located in mangrove roots, patch reefs, inner zone of the crest and fore reef (12-16m depth). In each site, we performed ten censuses for every habitat type in June and September 2009. A total of 11 507 individuals of 34 species were counted in a total of 400 censuses. We found significant differences in densities and size compositions among reef and mangrove habitats, supporting the species-specific use of coastal habitats. Adults were found in all habitats. Reef habitats, mainly patch reefs, seem to be most important for juvenile fish of most species. Mangroves were especially important for two species of snappers (Lutjanus apodus and L. griseus), providing habitat for juveniles. These species also displayed well defined gradients in length composition across the shelf. Rev. Biol. Trop. 62 (2): 589-602. Epub 2014 June 01.

El movimiento e intercambio de individuos entre hábitats son aspectos críticos para la dinámica y el éxito de las poblaciones de peces arrecifales. La segregación de tallas entre hábitats puede ser considerada como evidencia para la conectividad de hábitats y esta podría ser el primer paso para la formulación de hipótesis sobre migraciones ontogenéticas entre hábitats. El objetivo principal de nuestra investigación fue encontrar evidencia de diferencias entre hábitats en la distribución de tallas y densidad de especies de peces de arrecifes, las cuales pueden ser clasificadas, a priori, como especies con cambios ontogénicos en el hábitat, en una área extensa (~600 km²) de plataforma en el Caribe. Se realizaron censos visuales (métodos estacionario y de recorrido) de especies de peces seleccionadas en 20 sitios localizados en raíces de mangle, arrecifes de parche, la zona interna de la cresta arrecifal y el arrecife frontal (12-16m de profundidad). Se hicieron diez censos en cada sitio de los cuatro tipos de hábitat y se repitió este esquema en junio y septiembre 2009. Fueron contados un total de 11 507 individuos de 34 especies en un total de 400 censos. Se encontraron diferencias significativas en la densidad y composición por tallas entre los hábitats de arrecife y manglar. Estas diferencias, indicaron un uso variable de los hábitats costeros dependiendo de la especie. Los adultos fueron encontrados en todos los hábitats. Los hábitats de arrecifes, principalmente los arrecifes de parche, parecen ser muy importantes para los juveniles de peces de la mayoría de las especies en nuestra área de estudio. Los manglares fueron especialmente importantes para dos especies (L. apodus y L. griseus), que a lo largo de la plataforma fueron las únicas que mostraron gradientes bien definidos en las tallas.

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