Bayesian hierarchical modeling of amphibian communities and their pathogenic fungus (Batrachochytrium dendrobatidis) in Atlantic Forest streams

Author(s)

José Wagner Ribeiro Junior

• Document type: Doctoral Thesis
• Press: Rio Claro. 2018-08-23.
• Institution: Universidade Estadual Paulista (Unesp). Instituto de Biociências. Rio Claro
• Defense date: 2018-07-20
• Advisor: Tadeu de Siqueira Barros

Abstract

The Atlantic Forest is highly fragmented with less than 15% of its original cover remaining, however these fragmented forests harbour one of the most diverse amphibian communities with high proportion of endemic and rare species. The amphibians face many threats in this biome, such as habitat loss and infectious diseases. Thus, there is a high interested on understanding how the amphibians respond to the environmental gradients and how they are distributed on the landscape. Here, we used Bayesian hierarchical model to study the occurrence probability of amphibian species and communities and its pathogenic fungus (Batrachochytrium dendrobatidis, Bd) on Atlantic Forest streams. On the first chapter we assessed both species- and community-level responses of amphibians to important landscape-scale characteristics (i.e., forest cover, agriculture, catchment area, stream density, and slope). Our results showed that mean occupancy probability at the community level was positively related with the forest cover around the streams (buffer 200 m), while the agriculture had a negative effect. Furthermore, our results emphasized that many amphibian species have the highest occurrence probabilities in riparian zones with small catchment area within flat landscapes, although some species were associated with wider streams. On the second chapter, we evaluate the relative contribution of both stream and watershed-level characteristics, and the spatial component on the occurrence of stream-dwelling amphibians through Hierarchical Modelling of Species Communities (HMSC). We considered the hierarchical spatial structure of the studied system to test four models representing different dispersion ways (terrestrial, watercourse and both ways). Amphibians communities were related with both local and watershed-scale characteristics that were mediated by species traits. There was low support of relationship between the spatial component (i.e., dispersal limitation and mass effects) and species distribution in our study. On the last chapter, we evaluated how the occupancy and detection probabilities of the fungus B. dendrobatidis is related with biotic and abiotic variables. Our mains findings showed a high proportion of Atlantic Forest streams harbouring amphibians infected by Bd (mean = 75% of streams). Not accounting for imperfect detection underestimated the number of streams with infected animals. Occupancy probability of Bd was positively related with stream density and inversely related with amphibians diversity. Terrestrial-breeding species had a higher prevalence of Bd, thereafter. The forest cover is positively related with Bd prevalence; therefore, the detection probability of pathogen is higher in pristine areas. (AU)

• FAPESP's process: 14/07113-8 - Stream-dwelling anuran metacommunity structure and dynamics in the Atlantic Rainforest: a hierarchical approach that accounts for species imperfect detection
• Grantee: José Wagner Ribeiro Júnior
• Support Opportunities: Scholarships in Brazil - Doctorate