Functional Traits in Pollinator Communities

Abstract

Pollinator communities are declining globally, with functional trait composition -- the distribution of morphological, phenological, and behavioural traits across community members -- recognised as a more mechanistically informative indicator of pollination service delivery than species richness alone. Despite growing evidence that functional diversity metrics predict pollination outcomes better than taxonomic diversity, the determinants of functional trait composition in pollinator communities across land-use gradients and the consequences of trait composition shifts for plant reproductive success remain insufficiently quantified at the landscape scale. This study assembled a standardised functional trait dataset for 4,247 pollinator individuals from 247 species (bees: n = 184 species; hoverflies: n = 38; butterflies: n = 25) collected at 84 sites spanning an agricultural land-use intensity gradient across Central Europe, measuring 12 morphological traits (inter-tegular distance, tongue length, forewing area, body mass, and 8 ancillary traits) and recording phenological and behavioural data. Functional richness (FRic) declined significantly with land-use intensity (r = -0.74; p < 0.001), driven primarily by loss of specialist long-tongued bees and large-bodied bumblebees at intensively managed sites. Community weighted mean (CWM) tongue length declined by 34.7% from low- to high-intensity sites. Pollination success (seed set) in sentinel plants was significantly correlated with CWM tongue length (r = 0.68; p < 0.001) and FRic (r = 0.74; p < 0.001) but not with species richness alone (r = 0.38; p = 0.018) -- confirming that functional trait composition, not species richness, is the primary driver of pollination service delivery at the site level.