Understanding variation in abundance within species' ranges is fundamental for ecological and evolutionary theory and applied conservation science. The abundant-center model provides a general hypothesis based on basic ecological principles and macroscale biogeographic patterns: abundance should peak near the center of a species' range, where environmental conditions are most favorable, and decline towards the periphery. Despite longstanding influence in ecological thinking, consistent support for the ubiquity of abundant-center distributions remains elusive, and recent assessments have questioned the value of this paradigm altogether. We suggest that revisiting the simplifying assumptions that underly the model provides a productive path forward by clarifying predictions and revealing expectations for alternative distribution patterns. Towards this end, we use standardized abundance surveys of North American birds to reassess the prevalence of abundant-center distributions in geographic and climate space, test whether deviations are associated with predictable violations of assumptions, and provide more robust expectations. After accounting for common methodological pitfalls, we find that geographic centrality is generally indicative of centrality in climate space (confirming a key model assumption) and that abundant-center distributions occurred in 71% of passerines. To better understand exceptions, we introduce the concept of abundant-core distributions, of which the abundant-center is a special case. We find that 87% of species fit abundant-core expectations, with abundances peaked and generally declining from a core region within the range. Abundance cores tended to deviate from geographic center where topographic features complicate correspondence between geography and environmental conditions (e.g. the climatically heterogenous west). Such deviations were often associated with truncated climatic availability, with core regions offset towards the continental edge or climate extremes. Overall, our analyses suggest that abundant-center thinking provides a useful generalization for understanding spatial variation in abundance for many species. However, as with any model, its assumptions must be assessed within the context of given applications.

中文翻译：

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丰富的核心思想阐明了丰富的中心分布模式的例外情况

了解物种范围内丰度的变化是生态和进化理论以及应用保护科学的基础。丰富中心模型提供了一个基于基本生态学原理和宏观生物地理模式的一般假设：丰度应该在物种范围的中心附近达到峰值，那里的环境条件最有利，并向外围下降。尽管对生态思想有着长期的影响，但对普遍存在的丰富中心分布的一致支持仍然难以捉摸，最近的评估完全质疑了这种范式的价值。我们建议重新审视模型背后的简化假设，通过澄清预测和揭示对替代分布模式的期望，提供一条富有成效的前进道路。为此，我们使用北美鸟类的标准化丰度调查来重新评估地理和气候空间中丰度中心分布的普遍性，测试偏差是否与可预测的假设违背相关，并提供更稳健的预期。在考虑到常见的方法缺陷后，我们发现地理中心性通常表示气候空间的中心性（证实了一个关键的模型假设），并且 71% 的雀形目出现了丰富的中心分布。为了更好地理解异常，我们引入了 abundant-core 分布的概念，其中 abundant-center 是一个特例。我们发现 87% 的物种符合丰富的核心预期，丰度从该范围内的核心区域达到峰值并普遍下降。丰度核心往往偏离地理中心，地理中心的地形特征使地理和环境条件之间的对应关系变得复杂（例如气候异质的西部）。这种偏差通​​常与气候可用性的缩短有关，核心区域向大陆边缘或极端气候偏移。总的来说，我们的分析表明，丰度中心思维为理解许多物种丰度的空间变化提供了有用的概括。然而，与任何模型一样，其假设必须在给定应用程序的上下文中进行评估。核心区域向大陆边缘或极端气候偏移。总的来说，我们的分析表明，丰度中心思维为理解许多物种丰度的空间变化提供了有用的概括。然而，与任何模型一样，其假设必须在给定应用程序的上下文中进行评估。核心区域向大陆边缘或极端气候偏移。总的来说，我们的分析表明，丰度中心思维为理解许多物种丰度的空间变化提供了有用的概括。然而，与任何模型一样，其假设必须在给定应用程序的上下文中进行评估。