The dwarf caiman, Paleosuchus palpebrosus, is considered one of the smallest crocodilians. However, our surveys indicate that the species regularly reaches larger sizes than usually reported in the literature. Most individuals lose tail tips, and we did not encounter any individual with snout-vent length (SVL) > 70 cm that had an intact tail. P. palpebrosus attains SVL > 112.5 cm (equivalent to a total length with intact tail estimated from SVL of 210 cm) in streams around the Pantanal, 106 cm (198 cm) in flooded forest in central Amazonia, and 100 cm (187 cm) in flooded forest and around the Madeira-Guaporé River.
Rates of growth and survival in wild populations are affected by the physical environment, biotic interactions, and density-dependent processes, such as growth and fecundity. However, the relative importance of these factors in long-lived reptiles is poorly understood. We analyzed growth rates of Melanosuchus niger and Caiman crocodilus coexisting in two areas of the Brazilian Amazon with very different environmental characteristics. Growth rates of Caiman crocodilus at the two sites were similar, but M.niger grew more slowly in the area with higher productivity and higher density of caimans. Growth rates of the same species from other sites and of the temperate-zone Alligator mississippiensis indicate large differences among sites, but little evidence that these differences are primarily due to differences in productivity or temperature. Demographic models used to estimate sustained yields from caiman harvests should take into account the likely importance of density-dependent growth.
We studied the distribution of anurans in savanna, regrowth and mature forest at the mouth of the Tapajós river in Brazilian Amazonia. We sampled 31 sites on the right bank of the Tapajós river and on the shores of lakes nearby, and recorded all acoustic and visual observations of frogs. We found 18 anuran species: Leptodactylidae (8), Hylidae (7), Bufonidae (2) and Pseudidae (1). The distribution of species indicated that some species are generalists and others are restricted to certain habitats. The species at Alter do Chão are a subset of those found in forested sites in Amazonia. Lakes and forested areas had the greatest anuran diversity, but are also the areas most disturbed by tourist development and agriculture. Reduction of anuran diversity in the area could be minimized by concentrating development along the main beaches of the Tapajós river.
The formation of dominance hierarchies in which the female mates with a large dominant male is common among crocodilians. However, there is the possibility of polyandry, in which females mate with multiple partners during a single breeding season and generate offspring with multiple paternity. In the present study, eight pairs of heterologous primers developed for Alligator mississippiensis and Caiman latirostris were used to determine whether multiple paternity exists in the Black Caiman, Melanosuchus niger. For such, we analyzed 34 Black Caiman offspring from the Anavilhanas Archipelago in the Negro River (state of Amazonas, Brazil). The specimens came from six groups, each containing five or six hatchlings. Paternity exclusion and genetic identity indices were calculated to test the robustness of the microsatellite loci. Simple allele counts and maximum likelihood estimation of family clusters were used to determine the likelihood of occurrence of multiple paternity. Among the eight loci tested, five were effective at determining paternity, with paternity exclusion values close to 1.0 (QC = 0.92) and genetic identity values close to zero (IC < 0.01). Using the simple allele count, six cases of multiple paternity were detected and confirmed in three hatchling groups by four different microsatellite loci. However, maximum likelihood analysis indicated multiple paternity in all the groups analyzed, with five family clusters identified in one hatchling group alone. Considering that this species is listed according to IUCN as Lower Risk/Conservation Dependent, our results have direct conservation implications. Multiple paternity increases effective population size by maintaining genetic variation, and thus could be an important mechanism to maintain genetic diversity in isolated local populations.