observer_reliability_statistics_no_id_for_reviewers_only.xlsm from Neotropical mixed-species bird flocks in a community context

Mixed-species flocks are an important component of bird communities, particularly in the Neotropics, where flocks reach their highest diversity. The extent to which mixed-species flocks represent unique functional or ecological roles within communities, and how these attributes change over environmental gradients, however, is not well understood. We use a trait-based approach to examine functional aspects of flocking assemblages as they relate to those observed in the larger avian community across a 3000 m elevational gradient. Our results reveal similar ecological strategies among flocking species and the communities in which they occur, at the scale of the regional pool and across elevations. Trait variation in flocking and non-flocking assemblages is structured along two major axes defined by size- and resource-related traits. The trait space occupied by flocking species, however, represents only half (51%) that of the larger community. Similarly, the trait space of flocks across elevations is restricted compared to non-flocking species. The shared trait space across flock types represents small-bodied invertivores foraging in lower forest strata, traits associated with increased vulnerability to predation. The concentration of flocking species in functional trait space suggests high niche packing and either more overlap in ecological strategies or more finely divided niches relative to non-flocking species.This article is part of the theme issue ‘Mixed-species groups and aggregations: shaping ecological and behavioural patterns and processes’.

混合物种种群（mixed-species flocks）是鸟类群落的重要组成部分，尤其在新热带区（Neotropics），这类集群的物种多样性达到峰值。然而，关于混合物种种群在群落中所承载的独特功能或生态角色的覆盖范围，以及这些属性如何随环境梯度发生变化，目前尚缺乏充分的研究认知。我们采用基于功能性状的研究方法，在跨度达3000米的海拔梯度上，分析混合种群集群的功能特征，并将其与更大尺度的鸟类群落进行对比。研究结果显示，无论在区域种群尺度还是不同海拔区间，集群鸟类与其所在群落的生态策略均具有相似性。集群与非集群鸟类组合的性状变异，主要沿两大维度分布，分别由体型和资源相关的性状所主导。但集群物种所占据的功能性状空间仅为整个鸟类群落的一半（51%）。类似地，不同海拔下的混合种群集群的性状空间，相较于非集群物种也更为受限。各类混合种群共有的性状空间，对应着在森林下层觅食的小型食虫鸟类，这类性状与更高的被捕食风险相关。集群物种在功能性状空间中的集中分布，意味着相较于非集群物种，其生态位填充度更高，要么生态策略重叠程度更高，要么生态位划分更为精细。本文隶属于主题专刊“混合物种种群与集群：塑造生态与行为模式及过程”（Mixed-species groups and aggregations: shaping ecological and behavioural patterns and processes）。