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显示，腐叶栖蚂蚁（leaf-litter ants）的物种多样性存在海拔中峰模式。该多样性分布模式已在其他类群与区域中被观测到，但目前对于该模式的普遍性及其成因仍存在诸多未知。本研究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——展开调查，以验证蚂蚁多样性海拔中峰模式的稳健性。我们在整个中美洲范围内布设了56个采样位点。所有采样位点均处于冠层闭合的常绿湿润森林中，覆盖纬度跨度11°，海拔范围从近海平面至2600米。从每个采样位点的100份腐叶样本中提取蚂蚁，并将其鉴定至属或种水平。基于物种丰富度与多样性指标开展模型选择，以检验蚂蚁多样性最适配线性模型，还是支持海拔中峰模式的模型。同时通过线性模型分析多样性测度指标与温度、降水量及降水季节性之间的关联。物种丰富度测度指标与考虑相对丰度的多样性指数，在整个研究区域内均呈现与海拔相似的关联模式：即峰值位于约400米处的截尾钟形曲线。统计分析显示，三次方关系相较于二次方或线性关系更适配本研究数据。温度与多样性存在显著相关性，但无法解释钟形分布模式的成因。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预测钟形分布模式的出现。截尾钟形曲线的潜在成因包括低地生物群落衰减、中点吸引效应以及低地至山地群落的生态过渡带转换。对蚂蚁17个亚支系的分析大多呈现相同的截尾曲线模式，但其中6个支系表现出异常格局。这些异常支系的格局或许可通过其独特的行为或演化历史特征加以解释。