Avian Communities in the Amazonian Cangas Vegetation: Biogeographic Affinities, Components of Beta-Diversity and Conservation

ABSTRACT The Amazonian cangas is a vegetation type distributed as patches of open vegetation embedded in a matrix of tropical forest and that grows over iron-rich soils in the Serra dos Carajás region. To characterize cangas avifauna, we surveyed birds in eight patches varying from 43 to 1,366 hectares. Cangas avifauna has compositional affinities with savannas widespread throughout the Amazon and other biomes, and we estimate that more than 200 bird species occurs in this habitat. Species composition was relatively homogeneous, and the similarity among cangas patches was the dominant component of the beta-diversity. Bird communities in cangas patches exhibited statistically significant nested structure in respect to species richness and patch size. In contrast, the nested site arrangement was not affected by the isolation of patches. Number of species and composition are moderately affected by the area of cangas patches but not by its degree of isolation. To conserve this unique habitat are necessary a strict protection of carefully chosen patches of cangas and an investigation of the conservation value of secondary vegetation recovered by the mining companies.摘要 亚马逊坎加斯（cangas）是一类以斑块形式分布的开阔植被类型，镶嵌于热带森林基质之中，生长于卡拉加斯山脉（Serra dos Carajás）区域的富铁土壤之上。为表征坎加斯鸟类区系，我们对8块面积介于43至1366公顷的坎加斯斑块开展了鸟类调查。坎加斯鸟类区系与广泛分布于亚马逊及其他生物群系的稀树草原具有群落组成相似性，经估算该生境中栖息的鸟类物种数量超过200种。群落组成相对均质，坎加斯斑块间的物种相似性是β多样性（beta-diversity）的主导构成组分。坎加斯斑块的鸟类群落在物种丰富度（species richness）与斑块面积维度上呈现出统计学意义显著的嵌套结构（nested structure）。与之相反，斑块的隔离程度并未对嵌套式的站点分布格局产生影响。物种数量与群落组成受坎加斯斑块面积的影响中等，但不受其隔离程度的影响。为保护这一独特生境，需严格保护精心遴选的坎加斯斑块，并开展针对矿业公司恢复的次生植被保护价值的研究。