Data from: Effects of hummingbird morphology on specialization in pollination networks vary with resource availability

Specialization of species in interaction networks influences network stability and ecosystem functioning. Spatial and temporal variation in resource availability may provide insight into how ecological factors, such as resource abundance, and evolutionary factors, such as phylogenetically conserved morphological traits, influence specialization within mutualistic networks. We used independent measures of hummingbird abundance and resources (nectar), information on hummingbird traits and plant-hummingbird interactions to examine how resource availability and species' morphology influence the specialization of hummingbirds in three habitat types (forest, shrubs, cattle ranch) sampled over 10 sessions across two years in the southern Andes of Ecuador. Specialization of hummingbird species in the networks was measured by three indices: d’ (related to niche partitioning), generality (related to niche width) and PSI (related to pollination services). Specialization indices d’, generality and PSI of hummingbird species were influenced by resource availability. All indices indicated that specialization of hummingbirds increased when the availability of resources decreased. Variation in d’ was also explained by an interaction between resource availability and bill length; hummingbirds with a long bill switched from being more specialized than other species when resource availability was low to being similarly specialized when availability was high. Overall, our results highlight the importance of ecological and evolutionary factors determining the specialization of species in interaction networks. We demonstrate in particular that ecological gradients in resource availability cause substantial changes in consumers' foraging behavior contingent on their morphology. Changes in pollinator specialization along resource gradients can have impacts on ecosystem functions, such as pollination by animals.

物种在互作网络（interaction networks）中的特化程度，会对网络稳定性与生态系统功能产生影响。资源可利用性的空间与时间变异，可为解析生态因子（如资源丰度）与演化因子（如系统发育保守的形态特征）如何调控互利共生网络（mutualistic networks）内的物种特化提供思路。本研究依托蜂鸟丰度与资源（花蜜nectar）的独立测定数据、蜂鸟性状信息以及蜂鸟-植物互作数据，在厄瓜多尔南部安第斯山脉的三种生境（森林、灌丛、牧场）中开展了为期两年、共10次的采样调查，以此探究资源可利用性与物种形态如何影响蜂鸟的特化程度。蜂鸟物种在互作网络中的特化程度通过三项指标量化：d’（与生态位分化相关）、泛化指数（generality，与生态位宽度相关）以及PSI（与传粉服务功能相关）。研究发现，蜂鸟物种的三项特化指数d’、泛化指数与PSI均受资源可利用性的调控：所有指数均显示，当资源可利用性降低时，蜂鸟的特化程度显著升高。此外，d’的变异还可由资源可利用性与喙长的交互作用解释：在资源可利用性较低的情境下，长喙蜂鸟的特化程度高于其他物种；而当资源可利用性升高时，长喙蜂鸟与其他物种的特化程度并无显著差异。总体而言，本研究结果凸显了生态与演化因子在决定物种互作网络特化程度中的关键作用。我们特别证实，资源可利用性的生态梯度会依据消费者的形态特征，显著改变其觅食行为。传粉者沿资源梯度的特化变化，可对动物传粉等生态系统功能产生重要影响。