Martello Alcemar R, Hepp Luiz U, Kotzian Carla B
Rev Biol Trop. 2014 Mar;62(1):33-44.
Additive partitioning of species diversity is a promising approach for analyzing patterns of diversity in mollusk communities, especially their spatial distribution. Our aims were to assess the distribution of mollusk communities in Southern Brazilian streams, and to evaluate the partitioning of community diversity at different spatial scales. The study was carried out in the lower course of the Toropi River, one of the main tributaries of the Ibicui River Basin, in Southern Brazil. Four microbasins were considered: Sertão da Mata, Ribeirão, Tororaipi and Chiniquá, and sampling were undertaken in autumn, April and May 2009. Six sites were sampled in each stream: two in 1st-order segments, two in 2nd-order segments, and two in 3rd-order segments. All species found and the community as a whole, exhibited a clumped distribution. However, the variance-to-mean ratios for the Drepanotrema kermatoides and Heleobia bertoniana were higher than those of other species, suggesting a higher degree of aggregation. The additive partitioning of the species richness showed that the observed richness at smallest scale (alpha=within streams) represented 20.7%, and among-streams (beta1) represented 10.5% of the total richness. The richness and Shannon diversity index observed at the alpha scale, were higher than those observed at the first level of beta diversity scale (beta1=among-streams). The interaction between passive dispersal, tolerance to changes in some environmental variables, abiotic factors, and clumped distribution might have determined the spatial distribution of the communities studied. The greatest variation at the larger scales of analysis, involving among-orders and among-microbasins (beta2 and beta3, respectively) components, was expected, considering that the increase in distance leads to greater differences in richness (higher beta diversity). In conclusion, our results showed that the clumped distribution influenced the partition of the diversity of the mollusk communities in the streams studied. Dispersal methods and tolerance to variations in abiotic factors also have important roles in determining high alpha diversity. The partitioning of diversity showed that to preserve limnetic mollusks, it is important to preserve local areas, i.e., streams. Accordingly, conservation of streams on a local scale will contribute to conservation of the entire basin and maintenance of regional diversity (gamma).
物种多样性的加法划分是分析软体动物群落多样性模式，尤其是其空间分布模式的一种很有前景的方法。我们的目的是评估巴西南部溪流中软体动物群落的分布，并评估不同空间尺度下群落多样性的划分。该研究在巴西南部伊比奎河流域的主要支流之一托罗皮河下游进行。研究考虑了四个小流域：塞尔唐达马塔、里贝朗、托罗拉皮和奇尼夸，并于2009年4月和5月秋季进行了采样。每条溪流选取六个采样点：两个在一级河段，两个在二级河段，两个在三级河段。所有发现的物种以及整个群落都呈现出聚集分布。然而，克氏盘螺和伯氏黑螺的方差均值比高于其他物种，表明聚集程度更高。物种丰富度的加法划分表明，在最小尺度（α = 溪流内部）观察到的丰富度占总丰富度的20.7%，溪流间（β1）占10.5%。在α尺度观察到的丰富度和香农多样性指数高于在β多样性尺度的第一级（β1 = 溪流间）观察到的。被动扩散、对某些环境变量变化的耐受性、非生物因素和聚集分布之间的相互作用可能决定了所研究群落的空间分布。考虑到距离增加会导致丰富度差异更大（更高的β多样性），在更大尺度分析中，涉及阶间和小流域间（分别为β2和β3）成分的最大变异是预期的。总之，我们的结果表明，聚集分布影响了所研究溪流中软体动物群落多样性的划分。扩散方式和对非生物因素变化的耐受性在决定高α多样性方面也起着重要作用。多样性划分表明，为了保护淡水软体动物，保护局部区域即溪流很重要。因此，在地方尺度上保护溪流将有助于整个流域的保护和区域多样性（γ）的维持。
