Data from: Commonness, rarity and oligarchies of woody plants in the tropical dry forests of Mexico

We assessed woody plant communities in two widely separated forests in the tropical dry forest (TDF) biome of Mexico for evidence of similar patterns of species commonness and rarity. We used belt transects laid out along contour lines (i.e., constant elevation) and stratified across elevation gradients at sites in Jalisco and Oaxaca to sample woody plant species diversity, abundance, relative frequency and basal area. We assembled a combined species list and compared species found in both sites (shared) to species found in only one site, assessing whether the most and least common species at a site tended to be shared or unshared. Of the 8242 individuals sampled, 370 species or morpho-species were identified, with 222 species recorded at the Jalisco site and 270 at the Oaxaca site—122 (33%) species were shared across sites. Abundance, frequency and basal area of shared species were greater on average than for unshared species, and were positively correlated across sites. A subset of 68 shared species (18%) accounted for over half of all individuals encountered at the two sites. Species in the most common quartile were more likely to be shared than expected by chance, while species in the least common quartile were less likely. A genus-level analysis found similar patterns. Our findings suggest that the TDF of Pacific coast Mexico shows evidence of widespread dominance by a small subset of species. These findings have potentially important implications for predicting species composition, understanding the role of oligarchic species in ecological processes, and conserving rare species.

本研究针对墨西哥热带干燥林（Tropical Dry Forest, TDF）生物群区中两处相距甚远的森林开展木本植物群落调查，旨在探究两地物种常见度与稀有度的相似分布模式。本研究沿等高线（即恒定海拔）布设带状样带，并在哈利斯科州（Jalisco）与瓦哈卡州（Oaxaca）的样地中沿海拔梯度分层取样，以调查木本植物的物种多样性、多度、相对频度及基面积。研究人员整合得到联合物种名录，将两地共有的物种（共享物种）与仅在单一样地出现的物种进行对比，以此评估单样地中最常见与最稀有的物种更倾向于共享还是独有的分布特征。本次调查共取样8242株个体，共鉴定出370个物种或形态种；其中哈利斯科样地记录222种，瓦哈卡样地记录270种，两地共享物种共122种，占比33%。共享物种的多度、频度与基面积平均值均高于独有物种，且两地间的上述指标呈正相关关系。仅68种共享物种（占共享物种总数的18%）即占据了两地调查总个体数的一半以上。按常见度划分的四分位组中，位于最高常见度四分位的物种共享概率显著高于随机预期，而位于最低常见度四分位的物种共享概率则显著低于随机预期。属水平的群落分析也得到了相似的分布模式。本研究结果表明，墨西哥太平洋沿岸的热带干燥林群落呈现出由少数物种广泛占据优势的特征。上述研究结果对预测物种组成、理解寡头物种在生态过程中的作用以及珍稀物种保护均具有重要的潜在指导意义。