Seed dispersal by birds is a pivotal ecosystem function worldwide; yet, the rapid and ongoing global biodiversity loss poses a major threat to this essential ecosystem service. Seed dispersal effectiveness (SDE) is a key outcome of the interaction, represented by the product of seed dispersal quantity (number of seed dispersed) and quality (probability of recruitment of dispersed seeds). Therefore, identifying functional equivalent species in terms of SDE should become a key issue for bird conservation, since the effects of local extinctions on seed dispersal services may be weakened by remaining equivalent species. However, a method to quantitatively identify functional equivalent species in frugivorous bird assemblages is still lacking. To estimate SDE overlap between seed dispersers and assess whether two species may be functionally equivalent, I apply a novel nonparametric niche overlap index based on kernel functions and null models to test its statistical significance. For each bird species, I account for intraspecific variation in seed dispersal effectiveness to obtain a distribution of seed dispersal effectiveness values, an often neglected source of variation in seed dispersal assemblages. Non-significant differences in seed dispersal effectiveness overlap support the hypothesis that two species are functional equivalent, thus playing similar functional roles. The model proposed is applicable to any other quantity or quality component and is independent from the method or sampling design used to quantify SDE. The identification of functional equivalent species in seed dispersal assemblages adds to the theoretical framework of seed dispersal effectiveness and offers new insights into the ecology of the seed dispersal service provided by birds.

中文翻译：

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食果鸟类的种子传播有效性：识别鸟类组合中的功能等效物种

鸟类传播种子是世界范围内一个关键的生态系统功能；然而，迅速和持续的全球生物多样性丧失对这一重要的生态系统服务构成了重大威胁。种子传播效率 (SDE) 是相互作用的关键结果，由种子传播数量（传播的种子数量）和质量（传播种子的补充概率）的乘积表示。因此，根据 SDE 确定功能等效物种应该成为鸟类保护的关键问题，因为当地灭绝对种子传播服务的影响可能会被剩余的等效物种削弱。然而，仍然缺乏一种定量识别食果鸟类组合中功能等效物种的方法。为了估计种子传播者之间的 SDE 重叠并评估两个物种是否可能在功能上等效，我应用基于核函数和空模型的新型非参数利基重叠指数来测试其统计显着性。对于每种鸟类，我考虑了种子传播有效性的种内变异，以获得种子传播有效性值的分布，这是种子传播组合变异的一个经常被忽视的来源。种子传播有效性重叠的非显着差异支持两个物种功能等效的假设，因此发挥相似的功能作用。所提出的模型适用于任何其他数量或质量分量，并且独立于用于量化 SDE 的方法或抽样设计。