Functional traits and metacommunity theory reveal that habitat filtering and competition maintain bird diversity in a human shared landscape

Human shared landscapes cover much of Earth, yet their conservation value is contested. This controversy may persist because previous studies have examined species diversity, rather than the processes through which such diversity is maintained. For example, a site exhibiting high diversity may not actually bolster populations if the diversity is only maintained through net immigration. Recent research has begun to isolate the processes that maintain metacommunities and develop functional trait methods to identify these processes. However, the processes underlying bird communities remain obscure. Here, we leverage metacommunity theory, functional trait partitioning, and a Bayesian multispecies abundance model to assess whether a shared landscape – woody perennial polyculture farms – bolsters bird diversity. Such farms grow multiple species of food-producing woody perennials together with vegetative groundcover. We surveyed birds and their in situ functional traits across the US Midwest in traditional agriculture, woody perennial polyculture, prairie, and woods. We found that woody perennial polycultures exhibited the highest bird diversity and were the most preferred by many species (including threatened ones). Moreover, our functional trait analysis suggests that this diversity is maintained through habitat filtering and competition, rather than merely immigration. Thus, shared landscapes can likely conserve birds by providing a distinct habitat. These results suggest that woody perennial polyculture farms offer substantial potential to support bird populations in the US Midwest. Our study demonstrates the utility of in situ functional trait partitioning within a Bayesian framework to unmask ecological processes and help assess the conservation value of landscapes.

Methods
This data was collected in the US Midwest in summer 2018, and processed using R and Stan.

人类共享景观覆盖地球大部分区域，但其保护价值尚存争议。此类争议或持续存在，因过往研究多仅关注物种多样性本身，而非维持此类多样性的生态过程。举例而言，若某样地的高物种多样性仅依赖净物种迁入得以维持，则其实际上未必能有效支撑当地物种种群。近期研究已开始分离维持集合群落（metacommunities）的生态过程，并开发出功能性状分析方法以识别此类过程。但目前鸟类群落背后的相关维持过程仍不明晰。
本研究借助集合群落理论、功能性状分区方法与贝叶斯多物种种丰度模型，旨在评估一类共享景观——多年生木本混作农场——能否有效提升鸟类多样性。此类农场将多种可食用多年生木本植物与植被性地被作物进行复合种植。我们于美国中西部地区的传统农田、多年生木本混作农田、草原与林地四类生境中，开展了鸟类调查及其原位（in situ）功能性状测定。
研究结果显示，多年生木本混作农田的鸟类多样性最高，且受到诸多物种（包括受威胁物种）的青睐。此外，功能性状分析表明，该生境下的鸟类多样性是通过生境过滤与种间竞争得以维持的，而非仅依赖物种迁入。由此可见，共享景观可通过提供独特生境实现鸟类保护。上述结果表明，多年生木本混作农场在美国中西部地区具备支撑鸟类种群的巨大应用潜力。本研究证实了在贝叶斯框架下开展原位功能性状分区的实用性，可用于揭示生态过程并辅助评估各类景观的保护价值。
研究方法
本数据集于2018年夏季在美国中西部地区采集，使用R与Stan软件完成数据处理。