Data from: Environmental constraints on the compositional and phylogenetic beta-diversity of tropical forest snake assemblages

The ongoing biodiversity crisis increases the importance and urgency of studies addressing the role of environmental variation on the composition and evolutionary history of species assemblages, but especially the tropics and ectotherms remain understudied.
In regions with rainy summers, coexistence of ectothermic species may be determined by the partitioning of the climatic niche, since ectotherms can rely on water availability and thermoregulatory behaviour to buffer constraints along their climatic niche. Conversely, ectotherms facing dry summers would have fewer opportunities to climatic niche partitioning and other processes rather than environmental filtering would mediate species coexistence.
We used 218 snake assemblages to quantify the compositional (CBD) and phylogenetic (PBD) beta-diversity of snakes in the Atlantic Forest (AF) hotspot. We identify two AF regions with distinct climatological regimes: dry summers in the northern-AF and rainy summers in the southern-AF. While accounting for the influence of multiscale spatial processes, we disentangle the relative contribution of thermal, water-related, and topographic conditions in structuring the CBD and PBD of snake assemblages, and determine the extent in which snake assemblages under distinct climatological regimes are affected by environmental filtering.
Thermal conditions best explain CBD and PBD of snakes for the whole AF, whereas water-related factors best explain the structure of snake assemblages within a same climatological regime. CBD and PBD patterns are similarly explained by spatial factors but snake assemblages facing dry summers are more affected by spatial processes operating at fine to intermediate spatial scale whereas those assemblages in regions with rainy summers have a stronger signature of coarser-scale processes. As expected, environmental filtering plays a stronger role in southern-AF than northern-AF, and the synergism between thermal and water-related conditions is the key cause behind this difference.
Differences in climatological regimes within the tropics may affect processes mediating species coexistence. The role of broad-scale gradients (e.g. temperature, precipitation) in structuring tropical ectothermic assemblages is greater in regions with rainy summers where climatic niche partitioning is more likely. Our findings highlight the potential stronger role of biotic interactions and neutral processes in structuring ectothermic assemblages facing changes towards warmer and dryer climates.

当前持续的生物多样性危机使得探究环境变异对物种组合的组成与演化历史的影响的研究愈发重要且紧迫，但针对热带地区与变温动物（ectotherms）的相关研究仍较为匮乏。
在夏季多雨的区域，变温动物物种的共存可能由气候生态位（climatic niche）分化所决定——因为变温动物可借助水资源可利用性与体温调节行为，来缓冲其在气候生态位上所受的限制。与之相反，在夏季干旱的区域，变温动物进行气候生态位分化的机会更少，此时介导物种共存的将是环境过滤（environmental filtering）之外的其他过程。
本研究依托218个蛇类物种组合，对大西洋森林（Atlantic Forest, AF）生物多样性热点区内蛇类的组成β多样性（compositional beta-diversity, CBD）与系统发育β多样性（phylogenetic beta-diversity, PBD）进行量化。我们识别出大西洋森林内两个具有截然不同气候格局的区域：北部大西洋森林夏季干旱，南部大西洋森林夏季多雨。在考量多尺度空间过程影响的前提下，我们厘清了温度、水文与地形条件对蛇类物种组合的组成β多样性与系统发育β多样性的相对贡献，并明确了不同气候格局下的蛇类物种组合受环境过滤影响的程度。
就整个大西洋森林而言，温度条件最能解释蛇类的组成β多样性与系统发育β多样性；而在同一气候格局的区域内，水文相关因子则最能解释蛇类物种组合的结构。空间因子对组成β多样性与系统发育β多样性模式的解释力相近，但夏季干旱区域的蛇类物种组合受中低空间尺度的空间过程影响更为显著，而夏季多雨区域的蛇类物种组合则更多表现出大空间尺度过程的特征。正如预期，环境过滤在南部大西洋森林的作用强于北部大西洋森林，而温度与水文条件的协同作用正是这一差异的核心成因。
热带地区内部的气候格局差异可能会改变介导物种共存的过程。在夏季多雨、更易发生气候生态位分化的区域，大尺度梯度（如温度、降水）对热带变温动物物种组合结构的塑造作用更强。本研究结果表明，在面临气候向暖干化转变的背景下，生物相互作用与中性过程对变温动物物种组合的塑造可能发挥更为关键的作用。