Community-level body size structure is key to food web dynamics and stability, and can be affected by climate warming, because warming has reportedly led to changes in intra-specific body size or species range (affecting species composition), consequently shaping size structure. But little is known about whether and how these mechanisms collectively affect community-level size structure.

We collected Geometrid moths in 1965 and 2007 from Mt. Kinabalu (396 species from 1440 to 3675 m a.s.l.), which experienced a 0.7^oC warming during the 42 years. We investigated 1) whether intra-specific body size had changed, 2) whether species range shift had occurred and altered species composition, and 3) relative contribution of the two mechanisms to changes in community-level size structure.

We found species range shift, instead of intra-specific body size change, significantly contributed to the detected change in community-level size structure. In specific, species range shift changed local species composition and reduced average interspecific body size at higher altitude. This suggests that body size response to warming at higher level (community) could precede that at lower level (species) at decadal period.