Two basic patterns describe local plant community assembly and functioning: the species abundance distribution (SAD) and the distribution of species functional traits (TAD). These patterns have been extensively studied for dominant and rare plants, while subordinates, the species of intermediate abundance in a community, have received less research attention although this group is most species rich and important for community functioning. Here, we study the functional role of subordinate species (those covering the intermediate 50% of abundance ranks) using a large data set of Palearctic dry and semi-dry grassland plant communities and data on specific leaf area, seed mass and plant height. Theory predicts that dominant and subordinate plants should be functionally complementary. However, our findings indicate that species rank orders of SADs and TADs tend to be negatively correlated, causing the TAD to have higher evenness than the associated SAD. Subordinate species represented on average less than 15% of total plant abundance and trait space. Functional diversity of subordinates was lower than expected by a null model that assumed an equiprobable random distribution of trait values among plant species. Climate seasonality in combination with elevation, appeared to be the most important drivers of subordinate abundance and functional diversity. We conclude that subordinates differ from dominants in trait composition, leading to partial functional complementarity. We hypothesise that both groups are assembled through different processes and habitat filtering, partly triggered by local climatic conditions.

Climate change and anthropogenic alteration of landscapes negatively impact the abundance and diversity of plant and animal communities worldwide. Much less is known about the effects on phylogenetic diversity and community functioning. Here we use long-term observation data (1980 – 2022) from the Austrian Alps to assess how butterfly communities adjust community structures and functionality to increasing temperatures along the elevation gradient and how these changes are linked to trait expression and community functioning? Diversity significantly decreased at low and intermediate, and increased at high altitudes. Functional attribute diversity was significantly lower than expected by a random model at intermediate and high altitudes and increased with time at high, but not at intermediate and low altitudes. Multifunctionality significantly decreased at intermediate and high altitudes Phylogenetic diversity did not show significant temporal trends at low altitude, but significantly increased with time at intermediate and high altitudes. Multifunctionality was not significantly correlated with FAD, but decreased with increasing phylogenetic diversity. We conclude that the ongoing homogenisation of Alpine butterfly communities strongly affect species, functional and phylogenetic diversity. The directions of these changes heavily depend on altitude and therefore on specific climatic conditions. Higher altitudes face decreasing butterfly multifunctionality despite of increasing species richness due to climate induced altitudinal up-hill shifts of many species. The assessment of species richness and diversity alone, as provided by common species surveys, might give a false impression about the state and functioning of Alpine insect communities in the course of climate change.