Macrophyte functional composition is stable across a strong environmental gradient of a Neotropical floodplain

ABSTRACT Ecological communities are compared by the similarity or distinctness of their species. Taking into account community composition at a determined site, one could expect a similar reasoning to explain differences in both taxonomic and functional composition due to environmental gradients. We aim to evaluate spatial variation in functional composition of aquatic macrophyte assemblages in a Neotropical floodplain. The studied floodplain is characterized by encompassing different ecoregions considering both differences in environmental features and macrophyte taxonomic composition. Therefore, we hypothesized that macrophyte functional composition would differ among ecoregions but instead found limited differences in functional composition. There was only a little evidence that some life forms are more or less observed in certain ecoregions. Thus, the considerable environmental heterogeneity found at the ecoregion scale is reflected only in taxonomic, and not in functional composition. This result can be explained by different species having high functional redundancy: different functional traits could be recorded in all ecoregions. Therefore, we suggest that the functioning of the entire ecosystem is probably insured by species functional redundancy in this Neotropical floodplain. Nonetheless, we cannot rule out the fact that trait choice could affect interpretations, and so trait selection should be better explored, particularly for aquatic macrophytes.

摘要
生态群落的比较通常以其物种种群的相似性或分化程度为依据。结合特定样地的群落组成来看，我们可通过类似逻辑解释由环境梯度导致的分类学组成与功能组成差异。本研究旨在评估新热带洪泛平原（Neotropical floodplain）中水生大型植物（aquatic macrophyte）组合的功能组成空间变异。
本次研究的洪泛平原涵盖多个生态区，这些生态区在环境特征与大型植物分类学组成上均存在差异。据此我们提出假说：不同生态区间的大型植物功能组成会存在差异，但实际仅观测到有限的功能组成差异。仅有少量证据表明，某些生活型在特定生态区中的出现频率存在高低差异。
由此可见，在生态区尺度下观测到的显著环境异质性，仅体现在分类学组成上，而非功能组成。该结果可通过物种间较高的功能冗余性解释：所有生态区中均可观测到不同的功能性状。因此，我们认为在该新热带洪泛平原中，整个生态系统的功能稳定性可能由物种功能冗余性所保障。尽管如此，我们仍无法排除性状选择会影响研究解读这一可能性，因此应进一步探索性状筛选方法，尤其针对水生大型植物。