Influence of past and current factors on the beta diversity of coastal lagoon fish communities in South America

Aim: We aimed to assess the relative influence of past (Quaternary paleodrainage characteristics) and current factors on the beta diversity of freshwater fishes in coastal lagoons and explore the main processes involved.

Location: Atlantic coast of South America. Taxon: Fishes (173 species)

Methods: We built a dataset of species occurrence in 129 lagoons across eight freshwater ecoregions of the world (FEOWs) located between latitudes 0° and 36° and calculated beta diversity (βjac) and its turnover (βjtu) and nestedness (βjne) components. We used a partial Mantel test and multiple regressions on distance matrices to evaluate the importance of past and current factors, and of geographical distance in determining beta diversity. Past variables were those representing the historical freshwater habitat during the last glacial maximum (LGM), and contemporary variables were those related to current habitat.

Results: We found high values of βjac within the FEOWs, with βjtu prevailing over βjne. Both past (paleodrainage) and current (drainage area, salinity, and lagoon area) factors affected species dissimilarity (βjac = 46%) and its components (βjtu = 44% and βjne =20%), although explanation was, in part, shared with geographical distance. Individually, the influence of past factors was prevalent in beta diversity and its components.

Main Conclusions: The results suggest that major changes in the availability of freshwater habitats and connectivity since the Pleistocene must have affected the colonization, extinction and recolonization processes of fishes along the eastern coast of South America. We suggest that the high beta diversity values may result from limited dispersal after extinctions in the LGM and that the dissimilar freshwater fish communities currently seen were formed mainly by heterogeneous subsets of the regional species pool that persisted in landscape refuges during past sea level increases and then recolonized coastal lagoons.

Methods
We compiled fish species composition data for 129 lagoons along the Atlantic coast of South America between latitudes 0° and 36° S, which encompass eight freshwater ecoregions of the world (FEOW). The fish data consisted of a presence/absence matrix of species by lagoon. Most data were compiled by Petry et al. (2016), but we added new data by searching fish collection records in the SpeciesLink database (http://splink.cria.org.br/) and in primary research papers. A taxonomic and nomenclatural verification was performed across the dataset to validate all the species records. We included only lagoons that were subjected to specific community sampling protocols. Exclusively estuarine species or occasional marine species were not included, since we were interested in biogeographical processes related to freshwater species only.

研究目的：本研究旨在评估过去（第四纪古水系特征）与当前因子对沿海潟湖淡水鱼类β多样性的相对影响，并探讨其背后的核心驱动过程。

研究区域：南美洲大西洋沿岸。
研究类群：鱼类（共计173种）

研究方法：本研究构建了全球8个世界淡水生态区（Freshwater Ecoregions of the World, FEOW）内、纬度介于0°至36°之间的129个潟湖的物种出现数据集，并计算了雅卡尔型β多样性（βjac）及其周转组分（βjtu）与嵌套组分（βjne）。我们采用偏曼特尔检验（partial Mantel test）与距离矩阵多元回归分析，评估过去因子、当前因子及地理距离在决定鱼类β多样性中的重要性。其中，过去变量代表末次盛冰期（Last Glacial Maximum, LGM）的历史淡水生境，当代变量则与当前生境相关。

研究结果：我们在各世界淡水生态区内观测到较高的βjac值，且βjtu占比高于βjne。过去（古水系）与当前因子（水系面积、盐度及潟湖面积）均对物种相异度（βjac，解释度达46%）及其组分（βjtu解释度44%，βjne解释度20%）产生显著影响，不过部分解释度与地理距离存在重叠。单独分析时，过去因子对β多样性及其组分的影响占据主导地位。

主要结论：研究结果表明，更新世以来淡水生境的可用性与连通性发生重大变化，势必影响了南美洲东海岸鱼类的定殖、灭绝与再定殖过程。我们认为，较高的β多样性值可能源于末次盛冰期灭绝事件后物种扩散受限，而当前观测到的异质淡水鱼类群落，主要由区域物种库中的异质子集构成——这些子集在过去海平面上升期间存续于景观避难所，随后再度定殖沿海潟湖。

补充研究方法：我们整理了南美洲大西洋沿岸纬度0°至36°S之间的129个潟湖的鱼类物种组成数据，该区域涵盖全球8个世界淡水生态区（FEOW）。鱼类数据以“物种-潟湖”存在/缺失矩阵形式呈现。大部分数据源自Petry等人2016年的研究，我们通过检索SpeciesLink数据库（http://splink.cria.org.br/）及原始研究论文补充了新的数据。本研究对数据集开展了分类学与命名学验证，以确保所有物种记录的准确性。本研究仅纳入遵循标准化群落采样方案的潟湖，且排除专性河口物种或偶见海洋物种，因本研究仅关注与淡水物种相关的生物地理过程。