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.

物种沿海拔梯度的替代格局是山地类群中被广泛记录的分布模式。尽管已有研究证实种间竞争（interspecific competition）在热带生境中对确定物种海拔分布边界发挥着关键作用，但温带类群中该效应的相关研究仍较为匮乏。本研究以喜马拉雅山脉的两种留居山雀为研究对象，探究了繁殖季空间资源竞争与非繁殖季食物资源竞争在调控二者分布格局中的作用。研究结果表明，在鸣回放（song playback）实验与投食器试验中，高海拔分布的绿背山雀（Parus monticolus）在行为上均优于低海拔的灰山雀（Parus cinereus）。尽管灰山雀处于行为劣势，但在其海拔分布上限处，它们仍可与绿背山雀在人为改造生境中形成同域分布（sympatry）。本研究表明，限制高海拔绿背山雀分布、并促使灰山雀通过依附人类活动生境实现分布范围向上扩张的关键因素，并非种间竞争，而是同域分布区内自然生境的丧失。