Data from: Elevational replacement of two Himalayan titmice: interspecific competition or habitat preference?

Elevational species replacement is a widely documented pattern in montane species. Although interspecific competition has been shown to be important in setting species elevational limits in tropical habitats, its effect in species of temperate regions is poorly studied. We tested the role of interspecific competition for space in the breeding season and for food in the non-breeding season in mediating the distribution of two resident titmice species in the Himalayas. We show that high elevation green-backed tits (Parus monticolus) are behaviourally dominant over low elevation cinereous tits (Parus cinereus) in both song playback and feeder trials. Despite being subordinate, at their elevational upper limit, cinereous tits occur in sympatry in human modified habitats. Our study suggests that the loss of natural habitats in the sympatric zone, not interspecific competition, might be limiting the distribution of the high-elevation green-backed tits and facilitating an upward range shift through human association in cinereous tits.物种沿海拔更替是山地类群中被广泛记录的分布格局。尽管已有研究证实种间竞争（interspecific competition）在确定热带生境中物种的海拔分布上限方面发挥着重要作用，但该因素在温带类群中的影响却鲜有探讨。本研究以喜马拉雅地区的两种留居山雀为研究对象，探讨了繁殖季节空间资源种间竞争与非繁殖季节食物资源种间竞争对二者分布格局的调控作用。研究结果显示，在鸣唱回放与投食器实验中，高海拔的绿背山雀（Parus monticolus）均对低海拔的灰山雀（Parus cinereus）表现出行为优势。尽管灰山雀处于行为劣势，但在其自身的海拔分布上限区域内，它们会在人为改造生境中与绿背山雀形成同域分布。本研究表明，并非种间竞争，而是同域分布区内自然生境的丧失，限制了高海拔绿背山雀的分布，并推动灰山雀通过与人伴生的方式实现分布区向上扩张。