Despite the historical knowledge on amphibians of the Purus River basin, basic information on assemblages is fragmented, with gaps in knowledge existing at various scales, which limits conservation strategies. This study provides information on the composition, richness and abundance of the amphibian fauna in varzea environments and floating meadows of the oxbow lakes of the Middle Purus River between the Boca do Acre and Pauiní municipalities, Amazonas, Brazil. We sampled six oxbow lakes using forty-seven 200-meter transects, distributed among the ''floating meadows,'' ''high varzea'' and ''low varzea,'' from April to January 2014. We recorded 59 species, with the family Hylidae being predominant. This amphibian fauna represents approximately 19% of the species known for the Amazon, 28% for Amazonas State and 45% of the species recorded so far in the Purus River, increasing the richness of the basin to 132 species. Eight species were considered rare, and 29 are endemic to the Amazon. This study adds to the knowledge on the amphibian species of the Amazonian lowlands, including the expansion of known distributions, as well as increases the knowledge of several species that are locally rare, endemic and/or that are data deficient regarding distribution and ecology. Keywords: Amazon, floodplain, flood pulse, diversity, conservation. Resumo: Apesar do histó rico conhecimento sobre anfíbios ao longo da bacia do rio Purus, informac¸õ es bá sicas sobre as taxocenoses encontram-se fragmentadas, formando lacunas no conhecimento do grupo em diversas escalas e restringindo estratégias de conservac¸ã o. Este estudo apresenta a composic¸ão, a riqueza e a abundâ ncia da fauna de anfíbios em ambientes de vá rzea e bancos de macró fitas de lagos de meandro do médio Rio Purus, entre os municípios de Boca do Acre e Pauiní, Amazonas, Brasil. Conduzimos amostragens em seis lagos de meandro, através de 47 transectos de 200 metros, distribuídos entre os ambientes ''banco de macró fitas'', ''vá rzea alta'' e ''vá rzea baixa'', entre abril de 2013 e janeiro de 2014. Registramos 59 espécies, com predomínio de espécies da família Hylidae. Essa fauna de anfíbios representa aproximadamente 19% das espécies conhecidas para a Amazô nia, 28% para o estado do Amazonas e 45% do registrado até o momento para o rio Purus, elevando a riqueza da bacia para 132 espécies. Oito espécies foram consideradas raras e 29 sã o endêmicas da Amazô nia. Este estudo contribui para o conhecimento das espécies de anfíbios das terras baixas na Amazô nia, incluindo a ampliac¸ão da distribuic¸ã o e aumento do conhecimento sobre diversas espécies localmente raras, endêmicas e/ou com deficiência de dados sobre distribuic¸ã o e ecologia. Palavras-chave: Amazônia, planície de inundac¸ão, pulso de inundac¸ão, diversidade, conservac¸ão.

The genus Osteocephalus (Fitzinger, 1843) is represented by 23 species, of which nine occur in Brazil. Here we exntend the distribution of Osteocephalus castaneicola Moravec, Aparicio, Guerrero-Reinhard, Calderón, Jungfer & Gvoždík, 2009 and provide the first record for Acre state. We include an updated distribution map for the species.

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Despite the increasing amount of knowledge available regarding the ecological interactions between species, the dynamics of anurans in aquatic environments are little explored and understood. In this way, our work aims to assess which factors influence the composition and the ecological interactions of hylid anurans in oxbow lakes in the middle Purus River, Amazonas. We sampled three lakes with high, medium and low levels of connectivity twice, once during the flood and then in drought hydrological regimes. Variations in the hylid anuran assemblages and ecological interactions were tested as function of environmental niche, food resources, level of connectivity and hydrological regime. The availability of environmental resources and the availability of food resources were the best factors that explain the distribution of hylid anurans, which were also highly dependent on the variations between the hydrological regimes. The interactions between anurans, macroinvertebrates and macrophytes showed a modular and specialized structure, which varied according to the connectivity and hydrological regime of the lakes. Connectance showed an increasing trend from high to low connectivity lakes, suggesting that anurans had low trophic and environmental specialization in lakes with low connectivity. Hylids found in the lake of medium connectivity had higher values of trophic specialization and modularity. Our results illustrate the role of river-lake connectivity and annual hydrological cycle to maintain the aquatic biota and their interactions, and highlight the importance of floating meadows for the maintenance of biodiversity in floodplains.