The Arctic is projected to be severely impacted by changes in temperature and precipitation. Species react to these changes by shifts in ranges, phenology, and body size. In ectotherms, the patterns of body size clines and their underlying mechanisms are often hard to untangle. Mountains provide a space-for-time substitute to study these shifts along multiple spatial gradients. As such, mobility and dispersal capacity might conceal reactions with elevation. We test this influence on body size clines by comparing two common arthropods of the alpine tundra. We find that high mobility in the lycosid spider Pardosa palustris blurs elevational effects. Partially low mobility at least during development makes the carabid beetle Amara alpina more susceptible to elevational effects. Specific life-history mechanisms, such as brood care in lycosid spiders and holometabolic development in carabid beetles, are the possible cause.

The goal of our study was to close gaps in knowledge regarding Carabidae distribution and activity in response to microclimate. We aimed to characterise the spatiotemporal distribution of Carabidae species along multiple gradients, and explain the activity-abundance of assemblages and their indicator species using microclimatic measurements to identify key determinants of Carabidae activity-abundance and distribution. We sampled 32 alpine sites using pitfall traps and data loggers, and identified species assemblages linked to distinct habitat types that follow the snow-cover patterns and dynamics. Moreover, we linked the activity-abundance and distribution of assemblages and characteristic species to different temperature thresholds using mixed models and spatial cross-validation to assess variable importance. Our results demonstrate that alpine Carabidae species show markedly different responses to thermal thresholds, which reflect the patterns of snow cover. The importance of snow cover for species dist...