Abstract
Niche differentiation is a key concept in the field of ecology and refers to the process by which competing species within an ecological community partition utilization of environmental resources to achieve coexistence. The existence of niche differentiation is uniquely difficult to prove on account of the fact that historical interaction among species, which plays a key role in elucidating the current state of coexistence among species, is not well known. We created continuous niche gradients in nest‐site resources between two sympatric secondary cavity‐nesting birds, the green‐backed tit (Parus monticolus) and the russet sparrow (Passer cinnamomeus), and investigated whether nesting site is a factor contributing to limiting breeding overlap by regular inspection and 388,160 min of film recording. Our results indicate that although we manipulated nest site availability to be uniformly high along the habitat gradient, the two bird species have little overlap in nest sites and rarely compete for them. Furthermore, the green‐backed tit possessed a wide range of fundamental niche that covered that of the russet sparrow, while their reproductive time was largely segregated. The sparrow was more aggressive and outcompeted the tit in their overlapped range. These results suggest that even though nesting sites are crucial to the reproduction of cavity‐nesting birds, some other factor plays a more important role in limiting niche overlap between sparrows and tits in space and time. Given that these two cavity‐nesting birds continued to use different habitats and breed in segregated time after our manipulation, their relationship is better explained by the ghost of competition past theory.
Highlights
Diversity, competition, and coexistence are among ecology's clas‐ sical subjects
This study allows us to investigate whether nesting site was a factor contributing to limiting breeding overlap and may provide referential information to better understand the theories of niche differentiation
Our results suggest that the russet sparrow is a bet‐ ter competitor that has specialized in human settlement, while the green‐backed tit is inferior to the sparrow in competition but is gen‐ eralized to use a wide range of nesting sites
Summary
Competition, and coexistence are among ecology's clas‐ sical subjects. In an ecological community, various species live together as the end product of an assembly process by which or‐ ganisms interact with each other. The russet sparrow nests in holes in a tree, in‐house eaves or other building cavities, in embankments, or in stone walls, while the nest sites of the green‐backed tit cover a range from holes or cavities in tree trunks, old stumps, or fence posts, to holes in rocks, earth banks, holes in walls, or under house eaves (del Hoyo, Elliott, Sargatal, & Christie, 2013). This implies that the two species have similar requirement for nesting sites that they may compete for them after our manipulation. This study allows us to investigate whether nesting site was a factor contributing to limiting breeding overlap and may provide referential information to better understand the theories of niche differentiation
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