Evenness and diversity in Upper Cambrian – Lower Ordovician trilobite communities from the Central Andean Basin (Cordillera Oriental, Argentina)

Community evenness has recently received much attention, either because it is related to ecosystem functioning or because it may affect estimation of diversity. Temporal and environmental trends in diversity and evenness of trilobite communities during the Late Cambrian – Early Ordovician of the Cordillera Oriental (north-western Argentina) are here analysed. Richness and evenness increase through time in both deep subtidal (between fair-weather and storm wave base) and offshore (below storm wave base) communities. Two significant patterns are superimposed on this general trend: (1) the magnitude of the increase in evenness is much more pronounced in deep than in shallower settings, and (2) richness and evenness trajectories are decoupled (while a significant rise in evenness is recorded in the middle Tremadocian (Tr2), an increase in richness is delayed until the late Tremadocian (Tr3)). In contrast to expectations, a single family (Olenidae) is dominant in samples associated with this...群落均匀度（Community evenness）近期受到广泛关注，这既因其与生态系统功能息息相关，也因其可能会影响多样性估算结果。本文针对阿根廷西北部科迪勒拉东部（Cordillera Oriental）晚寒武世至早奥陶世时期三叶虫群落的多样性与均匀度的时间及环境变化趋势展开分析。无论是潮下深水环境（正常天气浪基面与风暴浪基面之间）还是远海环境（风暴浪基面以下）的群落，其物种丰富度与均匀度均随时间推移而提升。该整体趋势之上叠加了两项显著特征：其一，均匀度的提升幅度在深水环境中远比浅水环境更为显著；其二，物种丰富度与均匀度的变化轨迹发生解耦——特马豆克期（Tremadocian）中期（Tr2）记录到均匀度的显著上升，但物种丰富度的提升却延迟至特马豆克晚期（Tr3）才出现。与预期相悖的是，与本次研究相关的样本中，油栉虫科（Olenidae）为单一优势类群。