Taxonomic and phylogenetic beta diversity in headwater stream fish communities of the Paraná and Paraguai River basins

ABSTRACT Patterns of species replacement and richness differences along environmental gradients or ecoregions shed light on different ecological and evolutionary mechanisms acting on community structure. Communities of aquatic ecosystems of different watersheds are supposed to host distinct species and lineages. Quantifying and understanding the degree to which these differences are affected by environmental and biogeographical factors remains an open question for these environments, particularly in the Neotropical region. We investigated patterns of taxonomic and phylogenetic composition of headwater streams of the Paraná and Paraguai River basins to understand how local and biogeographical factors affect the assembly of fish communities. We also quantified taxonomic and phylogenetic beta diversity by decomposing them into nestedness and turnover components. We found that local environmental factors are the main factors influencing the composition of stream fish communities. Whereas pH affected both taxonomic and phylogenetic turnover, water velocity was responsible for phylogenetic turnover and pH was the main driver of phylogenetic nestedness. Our results indicate an effect of local environmental factors in determining the structure of headwater stream fish communities through a combination of a species sorting mechanism (water velocity and pH) and phylogenetic habitat filtering (pH).

摘要 沿环境梯度或生态区的物种替代模式与物种丰富度差异，可揭示作用于群落结构的不同生态与进化机制。不同流域的水生生态系统群落，理应孕育独特的物种与演化支（lineages）。针对这类水生环境，尤其是新热带区，量化并明晰这些差异受环境与生物地理因子影响的程度，仍是一个悬而未决的问题。本研究针对巴拉那河与巴拉圭河流域的源头溪流（headwater streams），探究其分类组成（taxonomic composition）与系统发育组成（phylogenetic composition）模式，以明晰局地与生物地理因子如何影响鱼类群落的组装过程。本研究还通过将分类β多样性与系统发育β多样性（beta diversity）拆解为嵌套性（nestedness）与周转（turnover）组分，对其进行了量化。研究结果表明，局地环境因子是影响溪流鱼类群落组成的主要因素。尽管pH值同时影响分类与系统发育周转，但水流速度仅对系统发育周转产生作用，而pH值则是系统发育嵌套性的主要驱动因子。本研究结果显示，局地环境因子通过物种分选机制（species sorting mechanism）与系统发育生境过滤（phylogenetic habitat filtering）的共同作用，决定了源头溪流鱼类群落的结构。