Bertuzzo Enrico, Carrara Francesco, Mari Lorenzo, Altermatt Florian, Rodriguez-Iturbe Ignacio, Rinaldo Andrea
Laboratory of Ecohydrology, École Polytechnique Fédérale Lausanne, 1015 Lausanne, Switzerland;
Laboratory of Ecohydrology, École Polytechnique Fédérale Lausanne, 1015 Lausanne, Switzerland; Ralph M. Parsons Laboratory for Environmental Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139;
Proc Natl Acad Sci U S A. 2016 Feb 16;113(7):1737-42. doi: 10.1073/pnas.1518922113. Epub 2016 Feb 1.
Elevational gradients of biodiversity have been widely investigated, and yet a clear interpretation of the biotic and abiotic factors that determine how species richness varies with elevation is still elusive. In mountainous landscapes, habitats at different elevations are characterized by different areal extent and connectivity properties, key drivers of biodiversity, as predicted by metacommunity theory. However, most previous studies directly correlated species richness to elevational gradients of potential drivers, thus neglecting the interplay between such gradients and the environmental matrix. Here, we investigate the role of geomorphology in shaping patterns of species richness. We develop a spatially explicit zero-sum metacommunity model where species have an elevation-dependent fitness and otherwise neutral traits. Results show that ecological dynamics over complex terrains lead to the null expectation of a hump-shaped elevational gradient of species richness, a pattern widely observed empirically. Local species richness is found to be related to the landscape elevational connectivity, as quantified by a newly proposed metric that applies tools of complex network theory to measure the closeness of a site to others with similar habitat. Our theoretical results suggest clear geomorphic controls on elevational gradients of species richness and support the use of the landscape elevational connectivity as a null model for the analysis of the distribution of biodiversity.
生物多样性的海拔梯度已得到广泛研究，然而，对于决定物种丰富度如何随海拔变化的生物和非生物因素，仍缺乏清晰的解释。在山区景观中，不同海拔的栖息地具有不同的面积范围和连通性特征，而根据集合群落理论，这些是生物多样性的关键驱动因素。然而，大多数先前的研究直接将物种丰富度与潜在驱动因素的海拔梯度相关联，从而忽略了这些梯度与环境基质之间的相互作用。在此，我们研究地貌在塑造物种丰富度格局中的作用。我们开发了一个空间明确的零和集合群落模型，其中物种具有依赖海拔的适合度以及其他中性特征。结果表明，复杂地形上的生态动态导致物种丰富度呈驼峰状海拔梯度的零期望，这是一种在实证中广泛观察到的模式。通过一种新提出的指标发现，当地物种丰富度与景观海拔连通性相关，该指标应用复杂网络理论工具来衡量一个地点与具有相似栖息地的其他地点的接近程度。我们理论结果表明，地貌对物种丰富度的海拔梯度具有明确的控制作用，并支持将景观海拔连通性作为分析生物多样性分布的零模型。
