Effects of exotic pastures on tadpole assemblages in Pantanal floodplains: assessing changes in species composition

Land use change has been identified as a major
driver of amphibian decline around the world. Yet we generally lack an
understanding of how conversion to exotic pastures affects freshwater
communities. This study examined tadpole assemblages in areas converted to exotic
pastures and native wooded grasslands in northern Pantanal wetland, Midwestern Brazil.
We tested the differences in site occupancy probability and assemblage
composition during a flood season. We registered thirteen tadpole species, but
only five were detected at levels suitable for occupancy modelling. For most
species, tadpole occupancy was higher at the beginning of the flood season.
Only Scinax fuscomarginatus occupancy was related with vegetation cover.
Occupancy probability for three species (Dendropsophus nanus, Physalaemus
centralis, and Physalaemus cuvieri) was associated positively with
species richness of fish. Multivariate analyses demonstrated that exotic
pastures hosted a different tadpole assemblage than native areas. The
assemblage composition gradient was associated with species richness of fish,
vegetation cover and volume of herbaceous vegetation and leaf litter. These
differences likely relate to specific traits of individual anuran species
(dietary plasticity, reproductive mode, and habitat preference). The study
showed that some generalist species were able to cope with replacement of
native vegetation by exotic species. However, management practices have
maintained many areas in the Pantanal at a stage of a near-pristine wetland ecosystem
and replacement of native vegetation by exotic pastures should be done with
caution.

土地利用变化已被识别为全球范围内两栖动物数量下降的主要驱动力。然而，我们对转变为异域牧场的转化如何影响淡水群落普遍缺乏理解。本研究调查了位于巴西中西部潘塔纳尔湿地北部，异域牧场和原生林地草原上的蝌蚪群落。我们测试了在洪水季节中，不同地点的占用概率和群落组成的差异。我们记录了十三种蝌蚪，但只有五种在适宜进行占用模型构建的水平上被检测到。对于大多数物种而言，蝌蚪的占用概率在洪水季节开始时较高。只有Scinax fuscomarginatus的占用概率与植被覆盖相关。三种物种（Dendropsophus nanus、Physalaemus centralis和Physalaemus cuvieri）的占用概率与鱼类物种多样性呈正相关。多元分析表明，异域牧场与原生地区拥有不同的蝌蚪群落。群落组成的梯度与鱼类物种多样性、植被覆盖和草本植物及落叶的体积相关。这些差异很可能与个别蛙类物种的特定性状（如饮食塑性、繁殖方式和栖息地偏好）有关。研究显示，一些泛食性物种能够适应原生植被被异域物种取代的情况。然而，管理实践使得潘塔纳尔地区的许多区域仍处于近乎原生湿地的生态系统阶段，因此应谨慎地替换原生植被以异域牧场。