Data from: The truncated bell: an enigmatic but pervasive elevational diversity pattern in Middle American ants

Studies on elevation gradients in Panama and Costa Rica have shown that leaf-litter ants exhibit a mid-elevation peak in diversity. This diversity pattern has been observed in other groups and regions, but uncertainty remains as to just how pervasive it is and what might explain it. Here we examine the robustness of the mid-elevation peak in ant diversity across the entire Middle American corridor, from Veracruz, Mexico, to Costa Rica. We sampled 56 sites distributed throughout Middle America. All were in closed-canopy evergreen wet forest, spanning 11° latitude, from near sea level to 2600 m elevation. Ants were extracted from 100 litter samples from each site and identified to genus or species. Model selection was performed on richness and diversity variables to test if ant diversity best fits a linear model or one allowing for a mid-elevation peak. Linear models were also used to examine the relationships among diversity measures and temperature, precipitation, and seasonality. Species richness measures and diversity indices that incorporate relative abundance show a similar relationship to elevation throughout the region: a truncated bell curve with a mode near 400 m. A cubic relationship is statistically favored over quadratic or linear. Temperature is a significant correlate with diversity, but does not predict a bell-curve. Precipitation and precipitation seasonality fail to explain much of the variability, and no combination of environmental variables predicts a bell curve. Potential causes of the truncated bell curve include lowland biotic attrition, mid-point attractors, and ecotonal transitions from lowland to montane communities. Analysis of 17 subclades within ants mostly showed the same truncated curve but six clades were anomalous. Distinctive behavioral or historical features potentially explain their patterns.

针对巴拿马与哥斯达黎加开展的海拔梯度研究表明，枯落物蚂蚁（leaf-litter ants）的多样性呈现海拔中峰模式（mid-elevation peak）。该多样性模式已在其他类群与区域中被观测到，但目前学界仍不清楚其普遍性究竟如何，亦未明确其背后的成因。在此研究中，我们针对中美洲走廊全域——从墨西哥韦拉克鲁斯州至哥斯达黎加——检验了蚂蚁多样性海拔中峰模式的稳健性。我们在中美洲全境布设了56个采样点，所有采样点均处于郁闭常绿湿润林生境中，纬度跨度达11°，海拔覆盖从近海平面至2600米的区间。我们从每个采样点的100份枯落物样本中分离提取蚂蚁，并将其鉴定至属或种级水平。针对物种丰富度与多样性变量开展模型选择分析，以检验蚂蚁多样性最适配线性模型，还是能够呈现海拔中峰特征的模型。同时通过线性模型分析多样性指标与温度、降水量及降水季节性之间的关联。物种丰富度指标与纳入相对丰度的多样性指数在整个研究区域内均呈现出与海拔一致的关联模式：即众数位于约400米处的截尾钟形曲线。统计结果显示，三次方关系相较于二次方或线性关系更适配该数据集。温度与多样性存在显著相关性，但无法解释钟形曲线模式的成因。降水量与降水季节性对多样性变异的解释力有限，且无任何环境变量组合能够复刻该钟形曲线模式。截尾钟形曲线的潜在成因包括低地生物群落损耗、中点吸引效应，以及低地与山地群落间的生态交错带过渡。对蚂蚁17个亚演化支的分析大多呈现出相同的截尾曲线模式，但其中6个支系呈现异常特征，这些异常支系的分布模式或可通过其独特的行为特征或演化历史特征加以解释。