Spatial variability in plant predation determines the strength of stochastic community assembly

High diversity is often poorly explained by trait-based deterministic models, in part because stochastic processes also influence community assembly. Testing how deterministic and stochastic processes combine to regulate diversity, however, has been limited by the spatial complexity of these interactions. Here, we demonstrate how spatial variability in small-mammal predation on plants, mostly by granivory, results in fine-scale switching between deterministically and stochastically regulated plant community assembly in an otherwise environmentally homogeneous tallgrass prairie. We initiated assembly with the uniform application of a 24-species mixture of prairie grasses and forbs, thereby setting the maximum level of diversity (γ-diversity). In field edges with higher densities of small mammals, traits reducing seed palatability deterministically produced homogeneous subsets of less palatable plant species within the first few months after planting (low α and β diversity). As small-mamm...基于功能性状的确定性模型往往难以解释高多样性格局，其部分原因在于随机过程同样会参与群落构建过程。然而，探究确定性与随机过程如何协同调控群落多样性的研究，常受限于这类相互作用的空间复杂性。本研究表明，在环境整体均质的高草草原生态系统中，以食籽行为为主的小型哺乳动物对植物的捕食活动存在空间异质性，该异质性可驱动植物群落构建在精细尺度上于确定性调控与随机调控模式之间切换。我们通过均匀播撒24种草原禾草与非禾本科草本植物的混合群落来启动群落构建过程，由此设定了最高水平的γ多样性（γ-diversity）。在小型哺乳动物密度较高的样地边缘，播种后的最初数月内，具备降低种子适口性功能性状的植物类群会通过确定性过程形成适口性较低的植物物种同质化子集，此时α多样性(α-diversity)与β多样性(β-diversity)均处于较低水平。当小型哺乳动物