Effects of environmental factors on the ecology and survival of a widespread, endemic Cerrado frog

Understanding the mechanisms that affect habitat use by vertebrates is critical for understanding how species are distributed across landscapes and how they cope with habitat change. The Brazilian Savanna (the Cerrado) has vegetation ranging from grassland to woodland savannas and harbors a rich and diverse amphibian fauna impacted by accelerated habitat loss. Here, we test the influence of vegetation type (from grassy scrubland to woodland) and distance from breeding sites (ephemeral water bodies) on body size, abundance, and survival of the frog Physalaemus nattereri in a natural metapopulation system of south-central Brazil. We also test whether body size is a significant predictor of population abundance. We found that the abundance of P. nattereri varies according to the mean snout-vent length of each metapopulation (sampling unit), as well as a higher estimated mortality rate in woodlands compared to typical Cerrado. Furthermore, we found no difference in estimated mortality among..., Sampling was performed monthly for 10 days, from August 2016 to July 2018, for a total of 24 field trips and 240 days of fieldwork. At each sampled vegetation type (campo cerrado, campo sujo, cerrado sensu stricto, and cerradão), three units of pitfall traps with drift fences were installed. Each unit corresponded to two 40-m trap lines, 60 m apart. Each trap line had four 100-L plastic buckets every 10 m, connected by a plastic drift fence 60 cm tall. Dorsal marks of individual frogs were recorded using digital cameras. Then, we performed a computer-assisted matching method, using the Wild-ID program. This software detects recaptures based on an algorithm of Scale Invariant Feature Transform, which extracts and combines the distinctive features in the image, regardless of size and orientation., Microsoft Excel
R

阐明影响脊椎动物栖息地利用的机制，对于理解物种在景观中的分布模式及其应对栖息地变化的策略至关重要。巴西稀树草原（Cerrado）的植被类型涵盖从草原到稀树林地的多个梯度，孕育了丰富多样的两栖动物区系，而该类群正受到栖息地加速丧失的威胁。本研究基于巴西南部中部的自然集合种群系统，探讨植被类型（从草本灌丛到林地）与繁殖位点（临时水体）的距离对纳特氏薄趾蟾（Physalaemus nattereri）的体型、种群丰度及存活率的影响，同时验证了体型是否可作为种群丰度的有效预测因子。研究结果显示，纳特氏薄趾蟾的种群丰度随各集合种群（采样单元）的平均吻肛长发生变化，且林地生境中的估算死亡率显著高于典型塞拉多生境。此外，本研究未发现[...]间的估算死亡率存在差异。本研究于2016年8月至2018年7月期间，每月开展为期10天的采样工作，累计完成24次野外考察，总野外工作日达240天。在各采样植被类型（塞拉多草原campo cerrado、灌丛草原campo sujo、狭义塞拉多cerrado sensu stricto及密灌稀树草原cerradão）中，均布设了3组带漂移围栏的陷阱装置。每组单元包含两条间距60米的40米长诱捕样线；每条样线每隔10米设置1个100升塑料桶，整条样线共设4个桶，样线之间由高度60厘米的塑料漂移围栏连接。研究人员使用数码相机记录每只青蛙的背部斑纹，随后采用Wild-ID软件开展计算机辅助匹配识别。该软件基于尺度不变特征变换（Scale Invariant Feature Transform, SIFT）算法，可提取并组合图像中的独特特征，不受图像尺寸与朝向的影响，从而识别重捕个体。数据分析采用Microsoft Excel及R软件。