Asymmetric environmental selection on intraspecific body size in Collembola communities along an elevational gradient in northern Japan

Body size is a crucial functional trait that influences the environmental filtering processes of animal communities. However, the role of intraspecific variations in soil invertebrate communities remains poorly understood. In this study, we investigated the influence of environmental changes on intraspecific body size variations in Collembola communities along an elevational gradient in northern Japan, using potential body length in the literature cited and realized body length actually measured. Our hypothesis posits that environmental conditions selectively filtered out smaller nymphs while sparing larger adults of Collembola, as stress tolerance, survival and mortality are directly influenced by body size in response to environmental severity. Calculating size quantiles based on observed realized individual body lengths, we found a stable size hierarchy among species across elevational sites. Species composition was significantly related with elevational gradient, with community-weighted means of smaller quantiles in body length increasing at higher elevations, while those of larger quantiles and adult body size remained unaffected. This suggests that environmental filtering predominantly influences the body size of smaller individuals, such as nymphs, but not larger adults within species. Our findings reveal asymmetric size selection among different life stages in soil animal communities.