Abstract

Functional diversity (FD) approaches have been increasingly used to understand ecosystem functioning in bird communities. These approaches typically rely on the assumption that species are perfectly detected in the field, despite the fact that imperfect detection represents a ubiquitous source of bias in biodiversity studies. This may be notably important in FD studies, because detection may depend on the functional traits used to compute FD metrics. However, little effort has been devoted to account for imperfect detection in FD studies, and therefore the degree to which species traits and detectability affects FD remains poorly understood. We predict that observed FD metrics may either underestimate or overestimate detection-corrected FD, because FD has multiple independent dimensions with different data properties. We assessed whether detection was related to bird traits (body mass, diet, and foraging stratum), accounting for habitat type, season, and phylogeny. We then used a multi-species occupancy model to obtain detection-corrected FD metrics (functional richness [FRic], functional evenness [FEve], and functional divergence [FDiv]), and compared observed and detection-corrected FD estimates in bird communities from east-central Argentina. Some functional types of birds (raptors and insectivores) were more easily overlooked, whereas others (seed and leaf eaters) were more easily detected. Some observed FD metrics underestimated detection-corrected FD (FRic and FDiv), whereas some others (FEve) overestimated detection-corrected FD. Both observed and detection-corrected FRic revealed differences between seasons, but not between habitat types. However, detection-corrected FEve and FDiv showed differences between seasons, contrary to observed estimates. Our results indicate that failure to account for unequal ease of detecting species can lead to erroneous estimates of FD because some functional types of birds are more easily overlooked. We outline some guidelines to help ornithologists identifying under which circumstances detection may be a concern and warn against the indiscriminate use of FD metrics without accounting for species detection.

中文翻译：

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在功能多样性估计中忽略物种可检测性的成本

摘要

功能多样性（FD）方法已越来越多地用于了解鸟类群落中的生态系统功能。尽管不完善的检测代表了生物多样性研究中普遍存在的偏见，但这些方法通常依赖于在田间完美检测物种的假设。这在FD研究中可能尤为重要，因为检测可能取决于用于计算FD指标的功能特征。然而，很少有努力致力于解决FD研究中的不完善检测，因此，对物种特征和可检测性影响FD的程度仍知之甚少。我们预测观察到的FD度量可能会低估或高估经检测校正的FD，因为FD具有具有不同数据属性的多个独立维度。我们评估了检测是否与鸟类特征（体重，饮食和觅食层）有关，并说明了栖息地类型，季节和系统发育。然后，我们使用多物种占用模型来获取经过检测校正的FD指标（功能丰富度[FRic]，功能均匀度[FEve]和功能差异[FDiv]），并比较了观察到的和经过检测校正的FD估计值。阿根廷中东部。某些功能类型的鸟类（猛禽和食虫类）更容易被忽视，而其他类型（种子和食叶动物）则更容易被发现。一些观察到的FD度量低估了检测校正的FD（FRic和FDiv），而其他一些（FEve）则高估了检测校正的FD。观察到的FRic和经检测校正的FRic都显示了季节之间的差异，但生境类型之间没有差异。然而，经检测校正的FEve和FDiv显示季节之间的差异，与观察到的估计相反。我们的结果表明，由于某些功能类型的鸟类更容易被忽视，因此无法解释不平等地发现物种可能导致FD的错误估计。我们概述了一些指南，以帮助鸟类学家确定在何种情况下可能需要进行检测，并警告不要在不考虑物种检测的情况下随意使用FD度量。