Spatial patterns of ferns in Evergreen Seasonal Forest in Amazonia-Cerrado transition

Abstract The climate and soil conditions are important predictors of spatial patterns and alpha diversity of plant populations. The spatial distribution of plant populations provides information about ecological processes that control the communities. In this study we investigated the richness and intra and interspecific spatial patterns of ferns in an Evergreen Seasonal Forest in the Amazonia-Cerrado transition. We described the spatial patterns by the univariate and bivariate O’ring function. We recorded four species of ferns samambaias (Trichomanes pinnatum, Lindsaea pallida, Adiantum incertum e Campyloneurum phyllitidis). All species exhibited the intraspecific spatial pattern aggregated. A positive interspecific pattern was observed between T. pinnatum and A. incertum, and L. pallida and A. incertum, however, we did not observe spatial relations between T. pinnatum and L. pallida. The strong climatic seasonality combined with a topographic homogeneity may be influencing the low species richness. The aggregation of these species is indicative that the dispersion limitation and the habitat structuration are determining their distribution. The species positive spatial associations may be reinforced by the environmental stress during the dry season. The absence of spatial relationships may be an indication that neutrality may partially explain the distribution of ferns in the studied forest.

摘要 气候与土壤条件是阐释植物种群空间格局与α多样性的关键预测因子。植物种群的空间分布可为解析调控群落构建的生态过程提供重要依据。本研究针对亚马逊-塞拉多（Amazonia-Cerrado）过渡带内的一处常绿季节性森林（Evergreen Seasonal Forest），探究了该区域蕨类植物的物种丰富度及种内、种间空间格局。我们采用单变量与双变量O环函数（O’ring function）对空间分布模式进行描述。本研究共记录到4种蕨类植物（samambaias），分别为膜蕨（Trichomanes pinnatum）、淡色陵齿蕨（Lindsaea pallida）、疑似铁线蕨（Adiantum incertum）以及带状书带蕨（Campyloneurum phyllitidis）。所有受试物种均表现出集群型的种内空间分布格局。在膜蕨与疑似铁线蕨、淡色陵齿蕨与疑似铁线蕨之间观测到正向种间空间关联；但膜蕨与淡色陵齿蕨之间未发现显著空间关联。强烈的气候季节性与地形均质化共同作用，可能是导致该区域物种丰富度偏低的原因。这些物种的集群分布表明，扩散限制与生境结构共同决定了其空间分布格局。旱季的环境胁迫可能进一步强化了物种间的正向空间关联。未观测到空间关联的现象，或许暗示中性过程可部分解释研究区域内蕨类植物的分布模式。