Adding Biotic Interactions into Paleodistribution Models: A Host-Cleptoparasite Complex of Neotropical Orchid Bees

Orchid bees compose an exclusive Neotropical pollinators group, with bright body coloration. Several of those species build their own nests, while others are reported as nest cleptoparasites. Here, the objective was to evaluate whether the inclusion of a strong biotic interaction, such as the presence of a host species, improved the ability of species distribution models (SDMs) to predict the geographic range of the cleptoparasite species. The target species were Aglae caerulea and its host species Eulaema nigrita. Additionally, since A. caerulea is more frequently found in the Amazon rather than the Cerrado areas, a secondary objective was to evaluate whether this species is increasing or decreasing its distribution given South American past and current climatic conditions. SDMs methods (Maxent and Bioclim), in addition with current and past South American climatic conditions, as well as the occurrences for A. caerulea and E. nigrita were used to generate the distribution models. The distribution of A. caerulea was generated with and without the inclusion of the distribution of E. nigrita as a predictor variable. The results indicate A. caerulea was barely affected by past climatic conditions and the populations from the Cerrado savanna could be at least 21,000 years old (the last glacial maximum), as well as the Amazonian ones. On the other hand, in this study, the inclusion of the host-cleptoparasite interaction complex did not statistically improve the quality of the produced models, which means that the geographic range of this cleptoparasite species is mainly constrained by climate and not by the presence of the host species. Nonetheless, this could also be caused by unknown complexes of other Euglossini hosts with A. caerulea, which still are still needed to be described by science.

兰花蜂（Orchid bees）是一类独特的新热带传粉昆虫类群，躯体色彩艳丽鲜亮。其中多个物种会自行构筑巢穴，另有部分物种被记录为营巢盗寄生者。本研究旨在评估：纳入宿主物种存在这类强生物互作因子，是否能够提升物种分布模型（Species Distribution Models, SDMs）对盗寄生物种地理分布范围的预测能力。本研究的目标物种为蓝胸兰花蜂（Aglae caerulea）及其宿主黑尾兰花蜂（Eulaema nigrita）。此外，鉴于蓝胸兰花蜂在亚马逊地区的分布频次高于塞拉多（Cerrado）稀树草原区域，本研究的次要目标为：结合南美过去与当前的气候条件，评估该物种的分布范围呈扩张还是缩减趋势。本研究采用物种分布模型方法（Maxent与Bioclim），结合南美当前与历史气候数据，以及蓝胸兰花蜂和黑尾兰花蜂的物种出现点位数据，构建分布预测模型。实验分别设置纳入与不纳入黑尾兰花蜂分布作为预测变量的两组方案，以构建蓝胸兰花蜂的分布模型。研究结果显示，蓝胸兰花蜂的分布几乎不受历史气候条件的影响；塞拉多稀树草原种群与亚马逊种群的存续时间至少可追溯至2.1万年前，即末次冰盛期（Last Glacial Maximum）。另一方面，本研究中纳入宿主-盗寄生互作复合体并未对模型的预测精度产生统计学上的显著提升，这表明该盗寄生物种的地理分布范围主要受气候因子限制，而非宿主物种的存在。尽管如此，这一结果也可能是由于目前学界尚未明确蓝胸兰花蜂的其他兰蜂族（Euglossini）宿主类群，相关类群仍有待科学描述与记录。