Data from: Untangling human and environmental effects on geographical gradients of mammal species richness: a global and regional evaluation

Different hypotheses (geographic, ecological, evolutionary or a combination of them) have been suggested to account for the spatial variation in species richness. However, the relative importance of environment and human impacts in explaining these patterns, either globally or at the biogeographic region level, remains largely unexplored. Here we jointly evaluate how current environmental conditions and human impacts shape global and regional gradients of species richness in terrestrial mammals. We processed IUCN global distributional data for 3939 mammal species and a set of seven environmental and two human impact variables at a spatial resolution of 96.5x 96.5 km. We used simple, multiple and partial regression techniques to evaluate environmental and human effects on species richness. Actual evapotranspiration is the main driver of mammal species richness globally. Together with our results at the biogeographic realm level, this lends strong support for the Hawkins et al. (2003) conjecture (i.e. global diversity gradients are best explained by the interaction of water and energy, with a latitudinal shift in the relative importance of ambient energy vs. water as we move from the poles to the equator). While human effects on species richness are not easily detected at a global scale due to the large proportion of shared variance with the environment, these effects significantly emerge at the regional level. In the Nearctic, Palearctic and Oriental regions, the independent contribution of human impacts is almost as important as current environmental conditions in explaining richness patterns. The intersection of human impacts with climate drives the geographic variation in mammal species richness in the Palearctic, Nearctic and Oriental regions. Using a human accessibility variable we show, for the first time, that the zones most accessible to humans are often those where we find lower mammal species richness.

已有诸多假说被提出以解释物种丰富度的空间变异，涵盖地理、生态、演化假说或其组合。然而，无论是在全球尺度还是生物地理区域尺度上，环境与人类活动影响在解释这些分布格局中的相对重要性，在很大程度上仍未得到深入探索。本研究联合评估了当前环境条件与人类活动影响如何塑造陆生哺乳动物物种丰富度的全球及区域梯度。我们处理了3939种哺乳动物的国际自然保护联盟（International Union for Conservation of Nature, IUCN）全球分布数据，以及一套包含7个环境变量与2个人类影响变量的数据集，空间分辨率为96.5×96.5千米。我们采用简单回归、多元回归与偏回归分析方法，评估环境与人类活动对物种丰富度的影响。全球尺度下，实际蒸散量（Actual evapotranspiration）是哺乳动物物种丰富度的主要驱动因子。结合我们在生物地理界（biogeographic realm）尺度上的研究结果，这一发现为Hawkins等人2003年的猜想提供了强有力的支撑——即全球多样性梯度最佳可通过水与能量的相互作用解释，且从极地向赤道移动时，环境能量与水分的相对重要性会发生纬度梯度上的转变。尽管由于与环境变量存在大量共享方差，人类活动对物种丰富度的影响在全球尺度上难以被精准检测到，但在区域尺度上，这些影响会显著显现。在近北极界、古北界与东洋界区域，人类活动影响的独立贡献度几乎与当前环境条件同等重要，可用于解释物种丰富度格局。在古北界、近北极界与东洋界区域，人类活动影响与气候的共同作用驱动了哺乳动物物种丰富度的地理变异。本研究首次通过人类可达性变量证实，人类可达性最高的区域往往也是哺乳动物物种丰富度最低的区域。