Explaining spatiotemporal variability in metacommunities is challenging because conducting empirical studies that link mechanisms across scales is difficult. We developed a stochastic model of epilithic algal succession in streams to better understand the underlying interactions that drive patch dynamics at three levels of spatial hierarchy: patch, channel habitat, and reach. The state of an algal patch is specified by one of nine community types, which are defined by growth form. Ninety-two empirical data sets of epilithic succession were used to estimate Markov transition probabilities among patch types as functions of inputs for light, nutrients, and current. Two additional probability matrices determine the effects of herbivory and disturbance based on user inputs. Testing model predictions of patch composition against independent empirical data indicated good correspondence based on resemblance metrics. Early in succession, most patches were occupied by prostrate and erect diatoms. These persisted under low light and nutrient conditions. Motile and stalked diatom patches characterized later stages when resources were moderate. Succession proceeded to mostly filamentous green algal patches under high resource levels. Sensitivity simulations indicated light most affected succession. Herbivory and disturbance increased the probability of prostrate diatom patches. We then used the model to examine how changes in abiotic and biotic parameters affect patch dynamics at different scales. Changes in nutrients or light affected patch diversity differently at the habitat vs. reach scale. Interactions with local resource levels within a channel habitat determined its alpha diversity. The proportion of channel habitat types within a reach, and their collective response to changes, determined beta diversity. Patch diversity within channel habitats generated by herbivory followed the predation hypothesis only when nutrients were low. At the reach scale, herbivory always increased patch similarity among channel habitats, lowering beta diversity. Diversity within channel habitats followed the intermediate disturbance hypothesis for a variety of habitats. Effects of disturbance on beta diversity at the reach scale depended on channel habitat heterogeneity. The stability of patches at the reach scale was highest when disturbance created high patch diversity, supporting the insurance hypothesis. The ideas generated can improve stream bioassessment methods and provide insight into mechanisms underlying patch dynamics in other ecosystems.

中文翻译：

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河流中附生藻类演替和斑块动态的随机模型

解释元社区的时空变异性具有挑战性，因为进行跨尺度关联机制的实证研究很困难。我们开发了溪流中附生藻类演替的随机模型，以更好地了解在空间层次的三个层次上驱动斑块动态的潜在相互作用：斑块、河道栖息地和范围。藻类斑块的状态由九种群落类型之一指定，这些群落类型由生长形式定义。使用 92 个上石演替经验数据集来估计斑块类型之间的马尔可夫转移概率，作为光、营养和电流输入的函数。两个额外的概率矩阵根据用户输入确定食草和干扰的影响。根据独立经验数据对补丁组成的测试模型预测表明基于相似性度量的良好对应。随后，大多数斑块被匍匐和直立的硅藻占据。这些在低光照和营养条件下持续存在。当资源适中时，活动的和有茎的硅藻斑块是后期阶段的特征。在高资源水平下，演替主要是丝状绿藻斑块。敏感性模拟表明光对演替的影响最大。食草和干扰增加了匍匐硅藻斑块的可能性。然后，我们使用该模型来检查非生物和生物参数的变化如何影响不同尺度的斑块动态。养分或光照的变化对栖息地和到达尺度的斑块多样性的影响不同。与渠道栖息地内当地资源水平的相互作用决定了其阿尔法多样性。河道内河道栖息地类型的比例，以及它们对变化的集体反应，决定了贝塔多样性。食草动物产生的通道栖息地内的斑块多样性仅在营养物质低时才遵循捕食假说。在河段尺度上，食草动物总是增加通道栖息地之间的斑块相似性，降低β多样性。河道栖息地内的多样性遵循各种栖息地的中间干扰假设。干扰对河段范围内贝塔多样性的影响取决于河道栖息地的异质性。当干扰产生高斑块多样性时，到达尺度的斑块稳定性最高，支持保险假设。