O endemismo em escala reduzida no espaço geográfico, na altitude e no habitat: estudo de caso do anuro de riacho Hylodes fredi Canedo Pombal-Jr. 2007 na Ilha Grande, Rio de Janeiro

Abstract

Information about the species geographic distribution and habitat use are important for management plans at population level. The anuran Hylodes fredi is endemic from Ilha Grande Island, coast of state of Rio de Janeiro, where it inhabits only the local streams. The knowledge around the effective distribution of H. fredi in the island is restricted, since the information about its occurrence refer only to the eastern region. The goal of this master dissertation was to expand the knowledge about H. fredi s distribution in geographic space and altitude, besides determining which habitat s characteristics have an influence on the species occupation between streams. We used encounter surveys between trails that connect locations and RAPELD plots, over the species activity time (diurnal), in rainy season months of 2014 and 2015. We evaluated the anuran frequency of occurrence between streams from continental and oceanic slopes and along altitudinal gradient. We evaluated the density of adult individuals per meter of stream edge, with encounter surveys on a 100 meters section in the streams found. During the encounter surveys inside streams, we also collected physical-chemical and habitat data. We tested how the abiotic data could influence occupancy and abundancy of H. fredi with occupancy modeling followed by model selection, using Akaike Information Criterium. We tested if H. fredi has preferences in habitat use, comparing the available habitat with what in fact was used. Our results demonstrate that H. fredi was found in both island slopes, being found in three out of 10 streams. The species showed more frequency of occurrence in streams of the oceanic slope (42.6% of the streams were occupied) in comparison to the continental slope (23.1%), suggesting that rainfall and human occupation may have influenced the species distribution. Hylodes fredi was recorded at altitudes between 60 and 420 meters, with a higher frequency of occurrence in streams between 200 and 350 meters, possibly related with the streams availability in this altitudinal range. The density of individuals inside the streams was similar to other Hylodidae anurans, with close to one individual every 20 meters of the stream edge where it inhabits. The model selection appointed a set of six variables that were the main influences in H. fredi occupancy and abundance between streams in Ilha Grande. It is suggestive that water conductivity, light intensity and air relative humidity had influence in the H. fredi reproductive activity. Streams with a high availability of vegetation and branches/trunks offer resting sites for the species, while sandy streams affect negatively the abundance because of the absence of shelters from predators. Hylodes fredi used mostly the rock habitat (80.6% of the records), possibly because the availability of shelters and the similar coloration with the rock surface, offering a safer place from predators