There have been important advances in understanding the relative importance of environmental and spatial processes for the variation in species composition across a set of local communities linked by dispersal (i.e. metacommunities). However, community composition-environment relationships change over time, and the mechanisms shaping such temporal variation in metacommunities encompassing large environmental gradients remain poorly understood. If the ability of statistical models to predict community composition-environment relationships depends on the sampling year, snapshot metacommunity studies would have limited implications, both theoretical and applied. Here, we partitioned the variation in compositional data of frog communities and asked if the relative importance of environmental and spatial components change over years at broad spatial scales (hereafter, protected areas in coastal and inland regions) of southeastern Brazil. These regions have marked differences in environmental characteristics as well as the size and composition of their regional species pool. Our results showed that the factors explaining the temporal variability in community composition-environment relationships were congruent for the inland region, which is less productive and characterized by harsh environmental conditions. In contrast, the relative importance of environmental and spatial components changed over years in the coastal region, which has more productive environments and benign conditions. Although snapshot studies will continue to provide important information about metacommunity dynamics, researchers have to be better able to incorporate the temporal variation inherent in community composition-environment relationships, which may be especially important in productive environments.

在理解环境和空间过程对通过分散连接的一组当地社区（即元社区）物种组成变化的相对重要性方面取得了重要进展。然而，群落组成-环境关系随着时间的推移而发生变化，并且在包含大环境梯度的元群落中形成这种时间变化的机制仍然知之甚少。如果统计模型预测群落组成-环境关系的能力取决于采样年份，那么快照元群落研究的理论和应用意义将有限。这里，我们划分了青蛙群落组成数据的变化，并询问在巴西东南部的广泛空间尺度（以下称为沿海和内陆地区的保护区）中，环境和空间组成部分的相对重要性是否随时间变化。这些区域在环境特征以及区域物种库的大小和组成方面存在显着差异。我们的结果表明，解释群落组成-环境关系的时间变化的因素与内陆地区一致，内陆地区生产力较低，环境条件恶劣。相比之下，环境和空间成分的相对重要性在沿海地区多年来发生了变化，沿海地区拥有更多的生产环境和良性条件。