Patterns of Species Richness and Turnover for the South American Rodent Fauna

Understanding the spatial distribution of species sheds light on the group’s biogeographical history, offers clues to the drivers of diversity, and helps to guide conservation strategies. Here, we compile geographic range information for South America’s diverse rodents, whose 14 families comprise ~50% of the continent’s mammalian species. The South American rodent fauna is dominated by independent and temporally staggered radiations of caviomorph and sigmodontine groups. We mapped species richness and turnover of all rodents and the principal clades to identify the main predictors of diversity patterns. Species richness was highest in the Andes, with a secondary hotspot in Atlantic Forest and some regions of considerable richness in Amazonia. Differences in richness were evident between the caviomorphs and sigmodontines, the former showing the greatest richness in tropical forests whereas the latter show—and largely determine—the all-rodent pattern. Elevation was the main predictor of sigmodontine richness, whereas temperature was the principal variable correlated with richness of caviomorphs. Across clades, species turnover was highest along the Andes and was best explained by elevational relief. In South America, the effects of the familiar latitudinal gradient in species richness are mixed with a strong longitudinal effect, triggered by the importance of elevation and the position of the Andes. Both latitudinal and elevational effects help explain the complicated distribution of rodent diversity across the continent. The continent’s restricted-range species—those seemingly most vulnerable to localized disturbance—are mostly distributed along the Andes and in Atlantic Forest, with the greatest concentration in Ecuador. Both the Andes and Atlantic Forest are known hotspots for other faunal and floral components. Contrasting patterns of the older caviomorph and younger sigmodontine radiations underscore the interplay of both historical and ecological factors in determining present-day diversity patterns.探明物种的空间分布格局，可为解析类群的生物地理历史提供依据，为多样性驱动因子研究提供线索，并助力保护策略的科学制定。本研究整合了南美洲多样啮齿类的地理分布范围数据，该类群涵盖14个科，约占该大陆哺乳动物物种总数的50%。南美洲啮齿动物区系以豚鼠类（caviomorph）与棉鼠类（sigmodontine）两大演化支独立且时序错开的辐射演化为主导。我们通过绘制全体啮齿类及主要演化支的物种丰富度与物种更替格局，以识别多样性分布格局的核心驱动因子。物种丰富度最高的区域为安第斯山脉，其次为大西洋森林，亚马孙地区部分区域同样拥有可观的物种丰富度。豚鼠类与棉鼠类的物种丰富度格局存在显著差异：豚鼠类在热带森林中物种丰富度最高，而棉鼠类的分布格局不仅自身呈现特定特征，还在很大程度上决定了全体啮齿类的整体多样性格局。海拔是影响棉鼠类物种丰富度的核心预测因子，而温度则是与豚鼠类物种丰富度相关性最高的环境变量。跨演化支分析显示，物种更替率最高的区域位于安第斯山脉沿线，其格局最佳的解释变量为海拔起伏。在南美洲，广为人知的物种丰富度纬度梯度效应，与由安第斯山脉的重要性及其地理位置所引发的强烈经度效应相互交织。纬度与海拔的双重效应，共同助力解析啮齿类多样性在该大陆的复杂分布格局。该大陆的狭域分布物种——这类物种对局域干扰的脆弱性通常更高——大多集中分布于安第斯山脉与大西洋森林，其中以厄瓜多尔的分布密度最高。安第斯山脉与大西洋森林均为其他动植物类群公认的生物多样性热点区域。豚鼠类作为更古老的演化支与棉鼠类作为较年轻的演化支，二者截然不同的辐射演化格局，凸显了历史与生态因子的相互作用在塑造当代多样性格局中的核心地位。