Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, Michigan, 48019, USA.
Department of Biology, University of Maryland, College Park, Maryland, 20742, USA.
Ecology. 2019 Aug;100(8):e02745. doi: 10.1002/ecy.2745. Epub 2019 Jun 12.
Although populations are phenotypically diverse, the majority of trait-based studies have focused on examining differences among species. The justification for this broadly applied approach is based on the assumption that differences among species are always greater than within species. This is likely true for local communities, but species are often broadly distributed across a wide range of environments and patterns of intraspecific variation might surpass differences among species. Therefore, an appropriate interpretation of the functional diversity requires an assessment of patterns of trait variation across different ecological scales. In this study, we examine and characterize patterns of leaf trait variation for species that are broadly distributed along an elevational gradient. We focus on seven leaf traits that represent a main axis of functional differentiation in plants reflecting the balance between photosynthetic efficiency, display, and stomatal conductance. We evaluated patterns of trait variance across ecological scales (elevation, species, populations, and individuals) and examined trait covariance at both within species and across species levels, along the elevation gradient. Our results show three key patterns: (1) intraspecific leaf trait variation for broadly distributed species is comparable to the interspecific trait variation, (2) the trait variance structure is highly variable across species, and (3) trait coordination between pairs of leaf traits is evident across species along the gradient, but not always within species. Combined, our results show that trait coordination and covariance are highly idiosyncratic across broadly distributed and co-occurring species, indicating that species may achieve similar functional roles even when exhibiting different phenotypes. This result challenges the traditional paradigm of functional ecology that assumes single trait values as optimal solutions for environments. In conclusion, patterns of trait variation both across and within species should be considered in future studies that assess trade-offs among traits over environmental gradients.
尽管种群在表型上具有多样性，但大多数基于特征的研究都集中在研究物种之间的差异上。这种广泛应用的方法的依据是，物种之间的差异总是大于物种内的差异。对于局部群落来说，这可能是正确的，但物种通常广泛分布在广泛的环境中，种内变异的模式可能超过物种间的差异。因此，对功能多样性的适当解释需要评估不同生态尺度上的特征变化模式。在这项研究中，我们研究并描述了沿海拔梯度广泛分布的物种的叶片特征变化模式。我们关注的是七个代表植物功能分化主轴的叶片特征，反映了光合作用效率、展示和气孔导度之间的平衡。我们评估了生态尺度（海拔、物种、种群和个体）上的特征方差模式，并在物种内和物种间水平上检查了特征协方差，沿着海拔梯度。我们的结果表明了三个关键模式：（1）广泛分布的物种的种内叶片特征变化与种间特征变化相当；（2）特征方差结构在物种间高度可变；（3）沿着梯度，物种间的叶片特征对之间存在明显的特征协调，但在物种内并非总是如此。综合来看，我们的结果表明，特征协调和协方差在广泛分布和共存的物种中具有高度的独特性，表明即使表现出不同的表型，物种也可能实现类似的功能角色。这一结果挑战了功能生态学的传统范式，即认为单一特征值是环境的最优解决方案。总之，在未来评估环境梯度中特征之间权衡的研究中，应该考虑跨物种和种内的特征变化模式。
