Science2013-10-18 8:42 PM

Hyperdominance in the Amazonian Tree Flora亚马逊河区树木的"超级统治"现象

Introduction Recent decades have seen a major international effort to inventory tree communities in the Amazon Basin and Guiana Shield (Amazonia), but the vast extent and record diversity of these forests have hampered an understanding of basinwide patterns. To overcome this obstacle, we compiled and standardized species-level data on more than half a million trees in 1170 plots sampling all major lowland forest types to explore patterns of commonness, rarity, and richness. 简介 近几十年来全世界都在努力为亚马逊盆地和圭亚那地盾(亚马逊古陆)的树群编制目录,但是这些森林如此广袤而且已有的记录又天差地别,这就限制了我们对盆地模式的进一步了解。为了跨越这些障碍,我们收集了物种层级的数据并整理出了标准,数据来自1170个试点的五十万棵树,这些树包括了所有低地森林的主要树种,我们想借此研究这些树群的共同点、常见度以及丰富性。 A map of Amazonia showing the location of the 1430 Amazon Tree Diversity Network (ATDN) plots that contributed data to this paper. The white polygon marks our delimitation of the study area and consists of 567 1° grid cells (area = 6.29 million km2). Orange circles indicate plots on terra firme; blue squares, plots on seasonally or permanently flooded terrain (várzea, igapó, swamps); yellow triangles, plots on white-sand podzols; gray circles, plots only used for tree density calculations. Background is from Visible Earth. CA, central Amazonia; EA, eastern Amazonia; GS, Guyana Shield; SA, southern Amazonia; WAN, northern part of western Amazonia; WAS, southern part of western Amazonia. More details are shown in figs. S1 to S3. 一张亚马逊古陆的地图显示了1430个亚马逊树种差异网络(ATDN)的试点位置,这些试点是本文的数据来源。白色多边形标示着我们队研究区域的定界,由5671个网格单元组成(地区面积为629万平方千米)。橘色圈表示陆地上的试点;蓝色方格表示常年或季节性洪涝地区(洪泛平原、湿地、沼泽);黄色三角形表示在白沙灰壤地区的试点;灰色圈表示只用于计算树木密度的试点;背景来自“可视地球”;CA表示中央亚马逊;EA表示东部亚马逊;GS表示圭亚那地盾;SA表示南部亚马逊;WAN表示西部亚马逊的北部地区;WAS表示西部亚马逊的南部地区。更多标示请见数字S1到S3。 Methods The ~6-million-km2 Amazonian lowlands were divided into 1° cells, and mean tree density was estimated for each cell by using a loess regression model that included no environmental data but had its basis exclusively in the geographic location of tree plots. A similar model, allied with a bootstrapping exercise to quantify sampling error, was used to generate estimated Amazon-wide abundances of the 4962 valid species in the data set. We estimated the total number of tree species in the Amazon by fitting the mean rank-abundance data to Fisher’s log-series distribution. 方法 六百万平方千米的亚马逊低地被分为一个单位,根据黄土回归模型计算出每个单位的树木密度,这个模型并不包括环境因素,只是按照试点树木的地理位置来计算。另一个运用自举法确定了取样错误数量的相似模型被用于计算除了数据组确定的4962个物种之外的大亚马逊地区的物种。我们把平均等级丰度数据用Fisher的对数级数分布表示出来,以此估算出亚马逊地区的树种数量。 Results Our analyses suggest that lowland Amazonia harbors 3.9 × 1011 trees and ~16,000 tree species. We found 227 “hyperdominant” species (1.4% of the total) to be so common that together they account for half of all trees in Amazonia, whereas the rarest 11,000 species account for just 0.12% of trees. Most hyperdominants are habitat specialists that have large geographic ranges but are only dominant in one or two regions of the basin, and a median of 41% of trees in individual plots belong to hyperdominants. A disproportionate number of hyperdominants are palms, Myristicaceae, and Lecythidaceae. 结果 经过分析我们认为低地亚马逊拥有3.9×1011种树并且有约16000种品种。我们找到227种“超级统治”品种(占总数的1.4%)其实非常常见,它们全体基本代表了亚马逊地区一半的树木。而那些最罕见的11000种品种却只占全部树木的0.12%。大部分超显性树种都是数量庞大而且地理范围宽广,但是只在碰地的一两个区域比较重要,各个试点都有41%的树木属于“超级统治”树种。棕榈科、肉豆蔻科及玉蕊科的超显性树种特别多。 Discussion The finding that Amazonia is dominated by just 227 tree species implies that most biogeochemical cycling in the world’s largest tropical forest is performed by a tiny sliver of its diversity. The causes underlying hyperdominance in these species remain unknown. Both competitive superiority and widespread pre-1492 cultivation by humans are compelling hypotheses that deserve testing. Although the data suggest that spatial models can effectively forecast tree community composition and structure of unstudied sites in Amazonia, incorporating environmental data may yield substantial improvements. An appreciation of how thoroughly common species dominate the basin has the potential to simplify research in Amazonian biogeochemistry, ecology, and vegetation mapping. Such advances are urgently needed in light of the >10,000 rare, poorly known, and potentially threatened tree species in the Amazon. 讨论 亚马逊所覆盖的树种不过区区227种,这个发现说明地球上最大的热带丛林的生物地理化学循环中,生物多样性只不过起了很小的作用。这些物种的超显性成因还是未知。无论是本身极具竞争力的优等属性还是1492年前就广泛存在的人类培植行为,从这两者得出的假说都还亟待验证。虽然有数据显示,空间分析能够有效预测亚马逊地区树群构成以及未研究地区的结构,但如果加入环境数据,就一定会有更好的成果。弄清楚常见物种如何在盆地中占据了主导地位这个问题,有助于简化亚马逊地区生物地球化学、生态及草本绘制等研究和工作。这样的优势对亚马逊一万多种我们知之甚少的,既罕见又很可能遭受威胁的树种是刻不容缓的。

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