Density, occupancy and detectability of tortoise species (Chelonoidis spp.) in the Atlantic Forest: implications for conservation and management

Abstract

ABSTRACT Understanding the distribution, abundance and detectability of species is pivotal for effective conservation and management strategies. This study investigated the populations of Chelonoidis denticulatus and Chelonoidis carbonarius within one of the largest remnants of the Atlantic Forest in Brazil (Vale Natural Reserve). The aim was to evaluate species abundance, factors influencing occupancy and detectability, and implications for conservation. Sampling occurred from 2015 to 2018 across 24 line transects. We measured climate and landscape variables potentially associated with species occurrence in each transect. We used the Royle–Nichols model to estimate abundance, while occupancy modelling assessed occupancy, detectability, and the effects of variables. The estimated population size of both species (C. denticulatus: 153 individuals, C. carbonarius: 105 individuals) was notably lower than in Amazonian areas. Detectability surged after rainfall, exceeding 70% with at least 55 mm of rain on the prior day. Occupancy of C. denticulatus correlated positively with forest cover, while both species were negatively affected by distance from water. The study’s findings signal potential critical conditions for Chelonoidis species in the Atlantic Forest. The small estimated populations, coupled with their reliance on water availability and forest cover for occupancy and detectability, pose significant conservation challenges. As climate change threatens the planet, these factors assume heightened significance. Given the alarming scenario of potentially critical population status within the Atlantic Forest, urgent attention is needed for robust conservation strategies. Strengthening ecological knowledge specific to this biome is essential to developing effective measures that counter the impacts of habitat loss, climate change and other threats. This study underscores the importance of preserving water resources and forest cover within the Atlantic Forest to secure the future of Chelonoidis species and highlights the need for comprehensive, targeted conservation efforts.