Environmental Predictors of Diversity in Recent Planktonic Foraminifera as Recorded in Marine Sediments

Global diversity patterns are thought to result from a combination of environmental and historical factors. This study tests the set of ecological and evolutionary hypotheses proposed to explain the global variation in present-day coretop diversity in the macroperforate planktonic foraminifera, a clade with an exceptional fossil record. Within this group, marine surface sediment assemblages are thought to represent an accurate, although centennial to millennial time-averaged, representation of recent diversity patterns. Environmental variables chosen to capture ocean temperature, structure, productivity and seasonality were used to model a range of diversity measures across the world’s oceans. Spatial autoregressive models showed that the same broad suite of environmental variables were important in shaping each of the four largely independent diversity measures (rarefied species richness, Simpson’s evenness, functional richness and mean evolutionary age). Sea-surface temperature explains the largest portion of diversity in all four diversity measures, but not in the way predicted by the metabolic theory of ecology. Vertical structure could be linked to increased diversity through the strength of stratification, but not through the depth of the mixed layer. There is limited evidence that seasonal turnover explains diversity patterns. There is evidence for functional redundancy in the low-latitude sites. The evolutionary mechanism of deep-time stability finds mixed support whilst there is relatively little evidence for an out-of-the-tropics model. These results suggest the diversity patterns of planktonic foraminifera cannot be explained by any one environmental variable or proposed mechanism, but instead reflect multiple processes acting in concert.学界普遍认为，全球多样性格局是环境因子与历史因子共同塑造的结果。本研究针对一系列已提出的生态学与进化学假说开展检验，这些假说旨在解释现代大型穿孔浮游有孔虫（macroperforate planktonic foraminifera）的岩芯顶多样性全球变异规律——该类群是一个拥有极其完整化石记录的演化支。在该类群中，海洋表层沉积物组合被认为能够精准反映近期多样性格局，尽管其记录是百年至千年尺度的时间平均结果。研究选取了能够表征海洋温度、水体结构、生产力与季节波动的环境变量，用于构建全球各大洋各类多样性指标的预测模型。空间自回归模型（spatial autoregressive models）结果显示，同一套宽泛的环境变量对四类基本独立的多样性指标均具有关键塑造作用，这四类指标分别为稀疏化物种丰富度（rarefied species richness）、辛普森均匀度（Simpson’s evenness）、功能丰富度（functional richness）以及平均进化年龄（mean evolutionary age）。海表温度对四类多样性指标的变异解释占比均为最高，但并未符合生态学代谢理论（metabolic theory of ecology）的预测逻辑。水体垂直结构可通过层化强度的提升与多样性增加产生关联，但与混合层深度无关。季节更替对多样性格局的解释力相对有限。现有证据表明，低纬度区域存在功能冗余现象。‘深时稳定性’进化机制（deep-time stability）得到了混合支持，而‘走出热带’模型（out-of-the-tropics model）的相关实证证据则相对匮乏。本研究结果表明，浮游有孔虫的多样性格局无法通过单一环境变量或已提出的任一机制加以解释，而是多种过程协同作用的综合体现。