Detritivores maintain stoichiometric homeostasis, but alter body size and population density in response to altitude induced stoichiometric mismatches

•Different functional groups within same taxon have diverse stoichiometric niches.•Stoichiometric niches vary among functional groups but not across elevations.•Stoichiometric mismatch between detritivores and resources changes with altitude.•Changes in stoichiometric mismatch with elevation affects body size and density.•Calcium, nitrogen, sodium and copper shape the body size and density of millipedes. Maintaining a balance between growth needs and available food resources is critical to the development of any organism. Ecological stoichiometry provides a theoretical basis for studying stoichiometric mismatches between organisms and their food resources. Recent studies have shown that detritivore taxa occupying different multidimensional stoichiometric niches (MSNs) exhibit different stoichiometric mismatch patterns. However, changes in stoichiometric mismatch patterns of different functional groups within the same taxon in response to changes in food resources are poorly understood. Here, we investigated changes in the stoichiometric mismatch between litter as major food resource and five functional groups of soil detritivores (millipedes; Diplopoda) for eleven elements along an altitudinal gradient from 800 to 1850 m on Changbai Mountain, Northeast China. We quantified MSNs and multidimensional stoichiometric mismatch patterns, and investigated changes with altitude and relationships with body size and population density. The concentration of chemical elements of litter varied significantly with altitude and this also was true for the trophic stoichiometric mismatch in millipedes. Furthermore, millipede stoichiometry homeostasis resulted in changing stoichiometric mismatches with changing litter element ratios. Element concentrations in litter, specifically N, Ca, P, Na and Cu, impacted the body size and population density of millipedes, with different elements correlating with individual functional groups. The results indicate that consumer-resource stoichiometric mismatches significantly affect detritivore populations, highlighting the predictive power of the multidimensional stoichiometry framework for detritivore community composition in context of environmental change.